U.S. patent application number 11/438244 was filed with the patent office on 2007-03-22 for apparatus and method for identifying frc and peep characteristics.
Invention is credited to Gary J. Choncholas, Ronald L. Tobia.
Application Number | 20070062533 11/438244 |
Document ID | / |
Family ID | 37517156 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070062533 |
Kind Code |
A1 |
Choncholas; Gary J. ; et
al. |
March 22, 2007 |
Apparatus and method for identifying FRC and PEEP
characteristics
Abstract
A ventilator for ventilating a patient also assists a clinician
in determining a suitable PEEP for the patient. For this purpose, a
graph or tabular display of a series of different value PEEPs and
corresponding functional residual capacities of the patient may be
provided. Or, the relationship between lung compliance and a series
of different values of PEEP may be provided. Or, the amount of the
lung volume recruited/de-recruited at various levels of PEEP may be
determined for use in selecting a desired PEEP. To this end, the
functional residual capacity of the lungs is determined for a first
PEEP level. The PEEP is then altered to a second level and a
spirometry dynostatic curve of lung volume and pressure data is
obtained. The lung volume on the dynostatic curve at a lung
pressure corresponding to the first PEEP value is obtained. The
difference between the functional residual capacity of the lungs at
the first PEEP level and that determined from the dynostatic curve
represents the lung volume recruited/de-recruited when changing
between said first and second PEEPs.
Inventors: |
Choncholas; Gary J.;
(Madison, WI) ; Tobia; Ronald L.; (Sun Prairie,
WI) |
Correspondence
Address: |
ANDRUS, SCEALES, STARKE & SAWALL, LLP
100 EAST WISCONSIN AVENUE, SUITE 1100
MILWAUKEE
WI
53202
US
|
Family ID: |
37517156 |
Appl. No.: |
11/438244 |
Filed: |
May 22, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11358573 |
Feb 21, 2006 |
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11438244 |
May 22, 2006 |
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60719329 |
Sep 21, 2005 |
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60719329 |
Sep 21, 2005 |
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Current U.S.
Class: |
128/204.23 ;
128/204.21 |
Current CPC
Class: |
A61M 2230/435 20130101;
A61M 2016/0027 20130101; A61M 16/024 20170801; A61M 2016/0039
20130101; A61M 2230/432 20130101; A61M 2016/0042 20130101; A61M
16/0833 20140204; A61M 2016/0036 20130101; A61M 16/0051 20130101;
A61B 5/091 20130101 |
Class at
Publication: |
128/204.23 ;
128/204.21 |
International
Class: |
A61M 16/00 20060101
A61M016/00 |
Claims
1-55. (canceled)
56. A ventilator for ventilating a patient and for determining a
relationship between a ventilator parameter and the functional
residual capacity of the patient, said ventilator comprising: at
least one gas flow control valve (20, 24, 54) in a flow path (32)
for breathing gases of the patient and a controller (26 or 74) for
said at least one gas flow control valve establishing and altering
a parameter of the ventilation supplied to the patient; a gas
analyzer (70) measuring a compositional characteristic of the
breathing gases of the patient; a sensor (62) measuring a
quantitative characteristic of the breathing gases of the patient;
a central processing unit (26 or 74) coupled to said gas analyzer
and sensor and determining the functional residual capacity of the
patient at a plurality of parameter values; and a display (102)
coupled to said central processing unit and displaying data
relating functional residual capacity to corresponding parameter
values.
57. The ventilator according to claim 56 wherein said at least one
gas flow control valve and controller establish and alter a
parameter comprising the PEEP supplied to the patient, said central
processing unit is further defined as determining the functional
residual capacity of the patient at a plurality of PEEPs, and said
display displays data relating functional residual capacity to
corresponding PEEP levels.
58. The ventilator according to claim 57 wherein said at least one
gas flow control valve and controller increment or decrement the
PEEP.
59. A ventilator according to claim 56 wherein said central
processing unit determines the functional residual capacity of the
patient by an inert gas wash-in or wash-out technique.
60. The ventilator according to claim 59 wherein the ventilator
provides breathing gases containing oxygen and nitrogen to the
patient and wherein said at least one gas flow control valve and
said controller alter the amount of oxygen contained in the
breathing gases supplied to the patient.
61. The ventilator according to claim 57 wherein said display
displays data relating PEEP to the corresponding functional
residual capacity in graphic form.
62. The ventilator according to claim 57 wherein said display
displays data relating PEEP to the corresponding functional
residual capacity in tabular form.
63. The ventilator according to claim 62 wherein the tabular
display includes an indication of PEEPe and PEEPi with the
corresponding functional residual capacity.
64. The ventilator according to claim 57 wherein said controller
sets one or more of initial PEEP, end PEEP, number of measurements,
or increment/decrement of PEEP alteration.
65. The ventilator according to claim 56 further defined as
including a memory for storing data relating functional residual
capacity to corresponding parameter values.
66. The ventilator according to claim 56 wherein said display
displays data obtained at different times.
67. The ventilator according to claim 56 wherein said at least one
gas flow control valve and controller alter one of a respiration
rate, expiration time, or inspiratory:expiratory ratio parameter;
said central processing unit determines the functional residual
capacity of the patient at a plurality of different values for the
altered parameter, and said display displays data relating
functional residual capacity to corresponding parameter values.
68. The ventilator according to claim 57 wherein said at least one
gas flow control value and said controller carry out a recruitment
maneuver and said display displays data obtained prior and
subsequent to the recruitment maneuver.
69. A method determining a relationship between a ventilation
parameter and the functional residual capacity of a ventilated
patient, said method comprising the steps of: (a) causing
alteration in a parameter of the ventilation supplied to the
patient; (b) determining the functional residual capacity of the
patient at a plurality of parameter values; and (c) displaying data
relating to functional residual capacity to corresponding parameter
values.
70. The method according to claim 69 wherein step (a) is further
defined as causing an alteration in the PEEP supplied to the
patient, step (b) is further defined as determining the functional
residual capacity of the patient at a plurality of PEEPs, and step
(c) is further defined as displaying data relating functional
residual capacity to corresponding PEEP levels.
71. The method according to claim 70 wherein step (a) is further
defined as incrementing or decrementing the PEEP.
72. The method according to claim 70 wherein step (b) is further
defined as determining the functional residual capacity of the
patient by an inert gas wash-in or wash-out technique.
73. The method according to claim 72 wherein the ventilated patient
is provided with breathing gases containing oxygen and nitrogen and
wherein step (b) is further defined as altering the amount of
oxygen contained in the breathing gases provided to the
patient.
74. The method according to claim 70 wherein step (c) is further
defined as displaying data relating PEEP to the corresponding
functional residual capacity in graphic form.
75. The method according to claim 14 wherein step (c) is further
defined as displaying data relating PEEP to the corresponding
functional residual capacity in tabular form.
76. The method according to claim 75 wherein step (c) is further
defined as displaying an indication of PEEPe and PEEPi with the
corresponding functional residual capacity.
77. The method according to claim 70 including a step for setting
one or more of initial PEEP, end PEEP, number of measurements, or
increment/decrement of PEEP alteration.
78. The method according to claim 69 further defined as storing
data relating to functional residual capacity to corresponding
parameter values.
79. The method according to claim 78 further defined as displaying
data obtained at different times.
80. The method according to claim 69 wherein step (a) is further
defined as causing an alteration in one of a respiration rate,
expiration time, or inspiratory:expiratory ratio parameter; step
(b) is further defined as determining the functional residual
capacity of the patient at a plurality of different values for the
altered parameter, and step (c) is further defined as displaying
data relating functional residual capacity to corresponding
parameter values.
81. The method according to claim 69 further including step of
carrying out a recruitment maneuver and step (c) is further defined
as displaying data obtained prior and subsequent to the recruitment
maneuver.
82. Apparatus for indicating recruitment/de-recruitment of lung
volume in association with varying levels of PEEP for a ventilated
patient, said apparatus comprising: at least one gas flow control
valve in a breathing gas flow path and a controller for said at
least one valve for ventilating the patient from a ventilator, said
at least one gas flow control valve and controller ventilating the
patient with a first level of PEEP, altering the PEEP to a second
level, different than said first level, and ventilating the patient
with the second level of PEEP; means for measuring the functional
residual capacity of the patient at one of the first and second
levels of PEEP; means for determining a spirometry dynostatic curve
for the breathing action of the patient at the other of said first
and second levels of PEEP; means for determining a lung volume
difference for the functional residual capacity at the one level of
PEEP and a point on the dynostatic curve for the other level of
PEEP corresponding to the one level of PEEP; and a display for
displaying the lung volume difference as recruited/de-recruited
volume in the lungs when changing between the first and second
levels of PEEP.
83. The apparatus according to claim 82 wherein said at least one
gas flow control valve and controller alters the PEEP from a higher
level to a lower level.
84. The apparatus according to claim 82 wherein said means for
determining a spirometry dynostatic curve is further defined as
determining a spirometry dynostatic curve on an absolute scale
using functional residual capacity.
85. The apparatus according to claim 82 wherein said display
displays the lung volume differences at various PEEPs in
conjunction with functional residual capacities of the lungs.
86. The apparatus according to claim 85 wherein said display
graphically displays the lung volume differences and functional
residual capacities.
87. The apparatus according to claim 85 wherein said display
displays the recruited/de-recruited volumes and functional residual
capacities in tabular form.
88. The apparatus according to claim 82 further including means for
performing a recruitment maneuver on the patient.
89. A method for indicating recruitment/de-recruitment of lung
volume in association with varying levels of PEEP for a ventilated
patient, said method comprising the steps of: (a) ventilating the
patient with a first level of PEEP, altering the PEEP to a second
level, different than said first level, and ventilating the patient
with the second level of PEEP; (b) measuring the functional
residual capacity of the patient at one of the first and second
levels of PEEP; (c) determining a spirometry dynostatic curve for
the breathing action of the patient at the other of said first and
second levels of PEEP; (d) determining a lung volume difference for
the functional residual capacity at the one level of PEEP and a
point on the dynostatic curve for the other level of PEEP
corresponding to the one level of PEEP; and (e) displaying the lung
volume difference as recruited/de-recruited volume in the lungs
when changing between the first and second levels of PEEP.
90. The method of claim 89 wherein step (a) alters the PEEP from a
higher level to a lower level.
91. The method according to claim 89 further including an initial
step of performing a recruitment maneuver on the patient.
92. The method according to claim 89 wherein step (c) is further
defined as determining a spirometry dynostatic curve on an absolute
scale using functional residual capacity.
93. The method according to claim 89 further defined as displaying
the lung volume differences at various PEEPs in conjunction with
functional residual capacities of the lung.
94. The method according to claim 93 further defined as graphically
displaying the lung volume differences and functional residual
capacities.
95. The method according to claim 93 further defined as displaying
the recruited/de-recruited volumes and functional residual
capacities in tabular form.
96. The method according to claim 89 further defined as repeating
the steps of the method by ventilating the patient at the other of
the first and second levels of PEEP, altering the PEEP to a third
level, and carrying out the corresponding steps of the method.
97. A ventilator for ventilating a patient and for determining a
relationship between a ventilator parameter and a functional
residual capacity characteristic of the patient, said ventilator
comprising: at least one gas flow control valve in a flow path for
breathing gases of the patient and a controller for said at least
one gas flow control valve for establishing and altering a PEEP
supplied to the patient; a gas analyzer measuring a compositional
characteristic of the breathing gases of the patient; a sensor
measuring a quantitative characteristics of the breathing gases of
the patient; a central processing unit coupled to said gas analyzer
and sensor for determining the functional residual capacity of the
patient at a plurality of PEEP values and for determining the
relationship between increments in the alteration in PEEP and
resulting differences in functional residual capacity; and a
display coupled to said central processing unit and displaying data
presenting the relationship determined by said central processing
unit to corresponding values of PEEP.
98. The ventilator according to claim 97 wherein said at least one
gas flow control valve and controller increment or decrement the
PEEP.
99. A ventilator according to claim 97 wherein said central
processing unit determines the functional residual capacity of the
patient by an inert gas wash-in or wash-out technique.
100. A ventilator according to claim 99 wherein said ventilator
provides breathing gases containing oxygen and nitrogen to the
patient and wherein said at least one gas flow control valve and
controller alter the amount of oxygen contained in the breathing
gases supplied to the patient.
101. The ventilator according to claim 97 wherein said display
displays data presenting the relationship determined by said
central processing unit to corresponding PEEP values in graphic
form.
102. The ventilator according to claim 97 wherein said display
displays data presenting the relationship determined by said
central processing unit to corresponding PEEP values in tabular
form.
103. The ventilator according to claim 102 wherein the tabular
display includes an indication of PEEPe and PEEPi with
corresponding PEEP values.
104. The ventilator according to claim 97 wherein said controller
sets one or more of initial PEEP, end PEEP, number of measurements,
or increment/decrement of PEEP alteration.
105. The ventilator according to claim 97 further defined as
including a memory for storing data relating the relationship
determined by means (c) to corresponding PEEP values.
106. A method determining a relationship between a ventilation
parameter and a functional residual capacity characteristic of a
ventilated patient, said method comprising the steps of: (a)
causing alteration in a PEEP supplied to the patient; (b)
determining the functional residual capacity of the patient at a
plurality of PEEP values; (c) determining the relationship between
increments in the alteration in PEEP and resulting differences in
functional residual capacity; and (d) displaying data presenting
the relationship determined in step (c) to 10 corresponding values
of PEEP.
107. The method according to claim 106 wherein step (a) is further
defined as incrementing or decrementing the PEEP.
108. The method according to claim 106 wherein step (b) is further
defined as determining the functional residual capacity of the
patient by an inert gas wash-in or wash-out technique.
109. The method according to claim 106 wherein step (d) is further
defined as displaying data presenting the relationship determined
in step (c) to corresponding PEEP values in graphic form.
110. The method according to claim 106 wherein step (c) is further
defined as displaying data presenting the relationship determined
in step (c) to corresponding PEEP values in tabular form.
111. The method according to claim 110 wherein step (d) is further
defined as displaying an indication of PEEPe and PEEPi with the
corresponding PEEP values.
112. The method according to claim 106 including a step for setting
one or more of initial PEEP, end PEEP, number of measurements, or
increment/decrement of PEEP alteration.
113. The method according to claim 106 further defined as storing
data relating the relationship determined in step (c) to
corresponding PEEP values.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application claims the priority of U.S.
Provisional Application No. 60/719,329, filed Sep. 21, 2005, and
comprises a continuation-in-part of U.S. patent application Ser.
No. 11/358,573, filed Feb. 21, 2006, which application also claims
priority of U.S. Provisional Application No. 60/719,329.
BACKGROUND AND SUMMARY
[0002] The present invention relates to an apparatus and method for
determining and displaying functional residual capacity data and
other pulmonary parameters, such as positive end expiratory
pressure (PEEP) data, for patients breathing with the aid of a
mechanical ventilator, such as a critical care ventilator. The
invention also determines and displays relationships between these
and other parameters.
[0003] Functional residual capacity (FRC) is the gas volume
remaining in the lungs after unforced expiration or exhalation.
Several methods are currently used to measure functional residual
capacity. In the body plethysmography technique, the patient is
placed in a gas tight body box. The patient's airway is sealingly
connected to a breathing conduit connected to the exterior of the
body box. By measuring lung pressures and pressures in the box, at
various respiratory states and breathing gas valve flow control
conditions, the functional residual capacity of the patient can be
determined.
[0004] Another technique for measuring functional residual capacity
is the helium dilution technique. This is a closed circuit method
in which the patient inhales from a source of helium of known
concentration and volume. When the concentration of helium in the
source and in the lungs has reached equilibrium, the resulting
helium concentration can be used to determine the functional
residual capacity of the patient's lungs.
[0005] A further technique for determining functional residual
capacity is the inert gas wash-out technique. This technique is
based on a determination of the amount of gas exhaled from the
patient's lungs and corresponding changes in gas concentrations in
the exhaled gas. The gas used for the measurement is inert in the
sense that it is not consumed by metabolic activity during
respiration. While a number of gases may be used for such a
measurement of functional residual capacity, it is convenient to
use nitrogen for this purpose.
[0006] In a straightforward example in which the patient is
initially breathing air, the lung volume forming the functional
residual capacity of the lung will contain nitrogen in the same
percentage as air, i.e. approximately 80%, the remaining 20% of air
being oxygen. In a wash-out measurement, the subject commences
breathing gases in which oxygen is at a different concentration
than 20%. For example, the patient commences breathing pure oxygen.
With each breath, nitrogen in the lungs is replaced by oxygen, or,
stated conversely, the nitrogen is "washed out" of the lungs by the
oxygen. While the breathing of pure oxygen could continue until all
nitrogen is washed out of the lungs, in most cases, the breathing
of oxygen continues until the nitrogen concentration in the exhaled
breathing gases falls below a given concentration. By determining
the volume of inert gas washed out of the lungs, and knowing the
initial concentration of the inert gas in the lungs, the functional
residual capacity of the lungs may be determined from these
quantities.
[0007] Methods for determining functional residual capacity in this
manner are well known and are described in such literature as The
Biomedical Engineering Handbook, CRC Press, 1995, ISBN
0-8493-8346-3, pp. 1236-1239, Critical Care Medicine, Vol. 18, No.
1, 1990, pp. 8491, and the Yearbook of Intensive Care and Emergency
Medicine, Springler, 1998, ISBN 3-540-63798-2, pp. 353-360. By
analogy to the above described wash out measurement technique, it
is also possible to use a wash in of inert gas for measurement of
functional residual capacity. Such a method and apparatus is
described in European Patent Publication EP 791,327.
[0008] The foregoing methods are used with spontaneously breathing
patients and are typically carried out in a respiratory mechanics
laboratory. But in many cases, patients that could benefit from a
determination of functional residual capacity are so seriously ill
as to not be breathing spontaneously but by means of a mechanical
ventilator, such as a critical care ventilator. This circumstance
has heretofore proven to be a significant impediment in obtaining
functional residual capacity information from such patients.
Additionally, the patient's illness may also make it impossible or
inadvisable to move the patient to a laboratory or into and out of
a body box for the determination of functional residual
capacity.
[0009] It would therefore be highly advantageous to have an
apparatus and method by which the functional residual capacity of
mechanically ventilated patients could be determined. It would be
further advantageous to associate the apparatus for carrying out
the determination of functional residual capacity with the
ventilator to reduce the amount of equipment surrounding the
patient and to facilitate set up and operation of the equipment by
an attending clinician. Such apparatus would also enable the
determination of functional residual capacity to be carried out at
the bedside of the patient, thus avoiding the need to move the
patient.
[0010] A single determination of functional residual capacity
provides important information regarding the pulmonary state of the
patient. However, it is often highly desirable from a diagnostic or
therapeutic standpoint to have available trends or changes in the
functional residual capacity of a patient over time.
[0011] It would also be helpful to be able to relate functional
residual capacity to other pulmonary conditions existing in the
lungs or established by the ventilator and to changes in these
conditions. For example, it is known that the pressure established
by the ventilator in the lungs at the end of expiration, the
positive end expiratory pressure or PEEP, affects the functional
residual capacity of the lungs.
[0012] Typically, an increase in PEEP increases functional residual
capacity. There are two components to the increased functional
residual capacity as PEEP is increased. One component is due to
stretching of the lung by the increased pressure. A second
component, particularly in diseased lungs, occurs from the effect
of PEEP during breathing by the patient. As a patient expires, the
pressure in the lungs drops until it approaches airway pressure. As
the pressure within the lungs drops, the alveoli or air sacs in the
lungs deflate. If alveolar sacs collapse completely, more pressure
is required upon inspiration to overcome the alveolar resistance
and re-inflate the alveolar sacs. If this resistance cannot be
overcome, the volume of such sacs are not included in the
functional residual capacity of the patient's lungs.
[0013] By applying PEEP, in the patient's airway, the additional
pressure in the patient's lungs keeps more of these alveolar sacs
from completely collapsing upon expiration and, as such, allows
them to participate in ventilation. This increases the functional
residual capacity of the patient's lungs and the increase is often
described as "recruited volume." Volume reductions are termed
"de-recruitments."
[0014] However, setting the PEEP too high can cause excessive lung
distension. There may also be compression of the pulmonary bed of
the lung, loading the right side of the heart and reducing the
blood volume available for gas exchange. Either of these
circumstances present the possibility of adverse consequences to
the patient.
[0015] It would, therefore, be desirable to provide an apparatus
and method by which a clinician could quickly, easily, and
definitely determine an optimal PEEP for a given patient at a given
point in the therapeutic regimen for the patient. An optimal PEEP
is one that keeps the lung open but avoids overpressurization of
the lung. It is often termed the "open lung PEEP."
[0016] Still further, action such as performing a suction routine,
administering a nebulized medication, or changing the ventilation
parameters of the ventilator can also influence functional residual
capacity and it would be helpful to be able to easily determine the
effect of such actions on functional residual capacity.
[0017] An apparatus and method that would possess the foregoing
characteristics and that would easily and cogently make such
information available would be highly beneficial in conveniently
obtaining a full understanding of the pulmonary condition of the
patient and how the patient is reacting to the mechanical
ventilation and to any associated therapeutic measures. The
clinician could then carry out appropriate action beneficial to the
patient in a timely and informed manner.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
[0018] An embodiment of the present invention comprises an
apparatus and method that achieves the highly advantageous features
noted above. Thus, with the present invention the functional
residual capacity of a mechanically ventilated patient may be
determined at the bedside of the patient without the need to move
the patient to a laboratory. By associating the apparatus with the
ventilator, only a single device need be employed to both ventilate
the patient and determine functional residual capacity.
[0019] The determined functional residual capacity may be
advantageously displayed in conjunction with earlier determinations
and in conjunction with other pulmonary conditions, such as PEEP.
Changes, or trends, in functional residual capacity over time may
thus be discerned, along with changes in the other pulmonary
conditions.
[0020] The foregoing provides an attending clinician with
significant information for assessing the state of, and trends in,
the functional residual capacity of the patient, as well as the
relationship between the patient's residual capacity and the other
factors, so that the clinician can fully discern the functional
residual capacity condition of the patient.
[0021] With respect to assisting the clinician in adequately
determining an optimal PEEP for the patient, as noted above, the
apparatus and method of the present invention determines and
displays related PEEP and functional residual capacity values. This
enables the clinician to note, for example, the point at which
increases in PEEP produce little, if any, further increases in
functional residual capacity.
[0022] The apparatus and method of the present invention also
determines and displays a showing of the amount of lung volume
recruited or de-recruited as the PEEP is changed. This allows the
clinician to distinguish between changes in functional residual
capacity due to lung stretching or contracting and those arising
from recruitment or de-recruitment.
[0023] Further features of the apparatus and method of the present
invention will be apparent from the following detailed description,
taken in conjunction with the associated drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a general diagram of a mechanical ventilator and
associated apparatus for ventilating a patient.
[0025] FIG. 2 shows an endotracheal tube with a tracheal pressure
sensor suitable for use in the present invention.
[0026] FIG. 3 shows a ventilator display unit presenting an initial
display screen for use in the present invention.
[0027] FIG. 4 is a chart showing the relationship among a plurality
of screens employed in the present invention.
[0028] FIG. 5 shows a display screen for displaying functional
residual capacity data and related data.
[0029] FIG. 6 shows a display for use in scaling the display shown
in FIG. 5.
[0030] FIG. 7 is a flow chart showing the steps for carrying out a
measurement of functional residual capacity.
[0031] FIG. 8 shows a display displaying a log of events and
actions that may impact the determination of functional residual
capacity.
[0032] FIG. 9 shows a display showing the effect of changes in PEEP
on functional residual capacity.
[0033] FIG. 9A shows a display showing changes in PEEP and
functional residual capacity before and after a recruitment
maneuver.
[0034] FIG. 9B shows a display showing the relationship of changes
in PEEP to corresponding changes in functional residual
capacity.
[0035] FIG. 10 shows a display showing spirometry data.
[0036] FIG. 11 shows a display for making setup adjustments for the
screen shown in FIG. 10.
[0037] FIGS. 12a and 12b show a display showing relationships among
functional residual capacity, PEEP, and recruited lung volume.
[0038] FIG. 13 is a flow chart showing the steps for carrying out a
method for obtaining the relationships shown in FIGS. 12a and
12b.
[0039] FIG. 14 is a graph showing the manner in which
recruited/de-recruited volume is determined by the present
invention.
DETAILED DESCRIPTION
The Mechanical Ventilator and Airway Gas Module
[0040] FIG. 1 shows mechanical ventilator 10 for providing
breathing gases to patient 12. Ventilator 10 receives air in
conduit 14 from an appropriate source, not shown, such as a
cylinder of pressurized air or a hospital air supply manifold.
Ventilator 10 also receives pressurized oxygen in conduit 16 also
from an appropriate source, not shown, such as a cylinder or
manifold. The flow of air in ventilator 10 is measured by flow
sensor 18 and controlled by valve 20. The flow of oxygen is
measured by flow sensor 22 and controlled by valve 24. The
operation of valves 20 and 24 is established by a control device
such as central processing unit 26 in the ventilator.
[0041] The air and oxygen are mixed in conduit 28 of ventilator 10
and provided to inspiratory limb 30 of breathing circuit 32.
Inspiratory limb 30 is connected to one arm of Y-connector 34.
Another arm of Y-connector 34 is connected to patient limb 36.
During inspiration, patient limb 36 provides breathing gases to
lungs 38 of patient 12. Patient limb 36 receives breathing gases
from the lungs of the patient during expiration. Patient limb 36
may include components such as a humidifier for the breathing
gases, a heater for the breathing gases, a nebulizer, or a water
trap (not shown). The breathing gases expired by patient 12 are
provided through patient limb 36 and Y-connector 34 to expiratory
limb 46 of breathing circuit 32. The expired breathing gases in
expiratory limb 46 are provided through valve 54 and flow sensor 56
for discharge from ventilator 10. Valve 54 may be used to establish
the PEEP for patient 12.
[0042] Patient limb 36 includes gas flow and pressure sensor 57
which may be of the type shown in U.S. Pat. No. 5,088,332. A pair
of pressure ports and lines 58, 60 are placed on either side of a
flow restriction in the sensor and the pressure difference
developed across the flow restriction is used by flow measurement
unit 62 in gas module 64 to measure gas flow in patient limb 36.
One of the pressure lines is connected to pressure measurement unit
66 to measure the pressure in patient limb 36. Sensor 57 also
provides for a gas sampling line 68 which is connected to gas
analyzer 70. Gas analyzer 70 may measure the amount of oxygen and
carbon dioxide in the breathing gases. Knowing the amounts of
oxygen and carbon dioxide in the breathing gases enables the amount
of nitrogen to be determined as the total amount less the amounts
of carbon dioxide and oxygen. Respiratory and metabolic gas module
64 may comprise that made and sold by GE Healthcare as a
Datex-Ohmeda MCOVX gas module. The output of gas module 64 is
provided in data bus 72 to central processing unit 74 in ventilator
display unit 76. Central processing unit 26 in ventilator 10 is
also connected to central processing unit 74 via data bus 78.
The Endotracheal Tube
[0043] To obtain an accurate indication of the pressure in lungs 38
of the patient 12, endotracheal tube 90 shown in FIG. 2 may be
used. Endotracheal tube 90 has end 92 for connection to patient
limb 36. In use, endotracheal tube 90 extends through the mouth and
into the trachea of patient 12 to provide an airway passage to
lungs 38.
[0044] Endotracheal tube 90 includes pressure sensor catheter 94
that extends from end 96 to provide a pressure sampling point that
is close to lungs 38 of patient 12 when the endotracheal tube is
inserted in the patient and can thus obtain a highly accurate
indication of the pressure in the lungs. An intermediate portion of
catheter 94 may lie within endotracheal tube 90. The proximal
portion exits the endotracheal tube and is connected via A-A to a
pressure transducer and to an auxiliary input to ventilator display
unit 76. The pressure obtained from catheter 94 is termed Paux.
While FIGS. 1 and 2 show a connection to ventilator display unit 76
for this purpose, the connection may, alternatively, be to gas
module 64.
[0045] An endotracheal tube of the type shown in FIG. 2 is
described in U.S. Pat. No. 6,315,739.
Ventilator Display Unit
[0046] Display unit 76 of ventilator 10 receives information from
the ventilator and gas module 64 and is used by the clinician to
control the pneumatic control components of ventilator 10 that
deliver breathing gases to patient 12 via data bus 78.
Additionally, central processing unit 74 in display unit 76 carries
out the determination of functional residual capacity,
recruited/de-recruited volumes, and other quantities employed in
the present invention. It will be appreciated that other CPU
configurations, such as a single CPU for the ventilator and its
display unit may be used, if desired.
[0047] Ventilator display unit 76 includes user interface 100 and
display 102. Display 102 is shown in greater detail in FIG. 3.
Display 102 is divided into a number of display portions 102a-g for
displaying inputted, sensed, and computed information. Display
portions 62a though 102f relate primarily to the operation of
ventilator 10 and the ventilation of patient 12 and are discussed
briefly below. Display screen portion 102g displays information and
relationships in accordance with the present invention, as
described in detail below.
[0048] Display portion 102a provides for the display of operating
information of ventilator 10. The portion shows the type of
ventilation being performed by ventilator 10, in the exemplary case
of FIG. 3, synchronized, intermittent, mandatory ventilation, or
SIMV-volume controlled ventilation. Portion 102a also provides a
display of operating information inputted into ventilator 10
including the percentage of oxygen for the breathing gases, tidal
volume (TV), breathing rate, inspiration time (T.sub.insp), amount
of positive end expiratory pressure (PEEP) and the pressure limit
(P.sub.limit) set for the volume controlled ventilation. To input
these operating parameters into ventilator 10, an appropriate one
of buttons 104a through 104f is actuated. Control knob 106 is
rotated to enter a desired value for the selected option and
pressed to confirm the new parameter value. Further ventilator
functions may be controlled by pressing a button that controls a
specialized function such as ventilator setup button 72 that
establishes other ventilation modes for patient 12, spirometry
button 74 for showing and controlling the display of spirometry
information, 100% 0.sub.2 button 76, nebulizer button 78, and
procedures button 80 that controls specialized procedures for
ventilator 10.
[0049] Display portion 102b of display 102 shows airway pressure
data as measured from sensor 57. Portion 102c shows textual
information relating to the flow of breathing gases to the patient
obtained from sensor 57, and portion 102d shows pressure data from
catheter 94 in the endotracheal tube 90 during ventilation of
patient 12.
[0050] Portion 102e of display 102 shows the information in regions
102b, 102c, and 102d in graphic form and includes an indication of
certain other operating information, such as the mode of
ventilation SIMV-VC, and whether certain features of the present
invention are operational or not.
[0051] Display portion 102f of display 102 shows additional data as
selected by the clinician. In the example of FIG. 3 end tidal
CO.sub.2 (E.sub.tCO.sub.2), lung compliance, expiratory alveolar
minute volume (MVe (alv)), respiratory rate, total positive end
expiratory pressure, and inspiratory alveolar minute volume (MVi
(alv)) are being shown.
[0052] Display portion 102a-f remain generally unchanged as the
present invention is practiced although, as noted above, the
clinician may select the information to be shown in certain
portions, such as portion 102f.
Display Screen of Present Invention
[0053] Display screen 102g is the part of display 102 employed in
the present invention. As shown in FIG. 4 and in FIGS. 5, 6, 8 and
9-12, the content of this screen will change, depending on the
inventive feature being utilized, the different content in screen
102g being identified as 102g1, 102g2, 102g3, etc. in the
appropriate figures of the drawing.
[0054] In general, each screen 102g will include a menu or control
portion 108, a graphic portion 110 and tabular portion 112. For
this purpose, graphic portion 110 contains a pair of orthogonal
axes by which data can be graphically presented. The clinician may
navigate and control the screen using control knob 106. Control
knob 106 is rotated to scroll through the menu options displayed in
menu portion 108, depressed to select a menu option, rotated again
to establish a numerical value for the selected option when
appropriate, and depressed again to enter the value into ventilator
display unit 76 or to confirm selection of the menu option.
[0055] FIG. 3 shows an initial content for screen 102g relating to
spirometry. As hereinafter noted, spirometry illustrates the
relationship between inspired gas volumes and the pressure in the
lungs as the patient breathes. The graphic form of the data is
normally in a loop, a portion of which is formed during inspiration
and the other portion of which is formed during expiration in the
manner shown in FIG. 10. The tabular portion 112 provides fields in
which various obtained and computed ventilation and lung properties
may be displayed.
[0056] Menu portion 108 allows the clinician to select a number of
options with respect to the display and use of the information
shown in graphic and tabular portions 110 and 112. Menu portion 108
also allows the clinician to select a further screen at 116 for
adjusting the scaling for the abscissa and ordinate of graph 110
and the setup for spirometry measurements at 118.
[0057] From menu portion 108, the clinician may also select screens
that allow the functional residual capacity (FRC) features of the
present invention and the spirometry features of the present
invention to be carried out by selecting items 120 and 122,
respectively. The spirometry features of the present invention are
identified by applicant as SpiroDynamics or the abbreviation
SpiroD.
[0058] FIG. 4 shows the architecture of the screens 102g used in
the present invention. As noted above, the spirometry screen shown
in FIG. 3 as screen 102g1 is the initial screen appearing as screen
102g. As noted above, associated with this screen are screens for
spirometry scaling and spirometry setup.
[0059] By means of menu items 120 and 122, the clinician can select
either a screen relating to functional residual capacity, namely
screen 102g2 shown FIG. 5 or a screen relating to SpiroDynamics
comprising screen 102g3 of FIG. 10. The screen format of FIG. 5 is
termed "FRC INview." The view of FIG. 10 is termed "spiroD".
[0060] The FRC INview showing of 102g2 includes screen shown in
FIG. 6 that allows for scaling of the quantities shown graphically
in FIG. 5.
[0061] A further selection on the FRC INview screen allows the
clinician to select the FRC log screen shown in FIG. 8 as screen
102g4.
[0062] Selections on either of the FRC INview screen 102g2 or the
SpiroDynamic screen 102g3 allows selection of a PEEP INview screen
shown in FIG. 9 as 102g5. As hereinafter described, this screen
allows the clinician to see the relationship between functional
residual capacity and PEEP to assist in selecting an appropriate
PEEP for patient 12.
[0063] Finally, an on/off selection option in PEEP INview screen
102g5 allows the clinician to display lung INview screen 102g6
shown in FIG. 12. The information contained in this screen relates
functional residual capacity, PEEP, and recruited/de-recruited lung
volumes to further assist the clinician in setting the appropriate
level of PEEP.
FRC Determination and Display
[0064] The flow chart of FIG. 7 shows a method for determining and
displaying functional residual capacity information for patient 12.
The clinician uses a screen in the format of 102g2 of FIG. 5. It is
assumed that the clinician has previously established an oxygen
percentage for the breathing gases to be provided by ventilator 10
using button 104a, control knob 106 and screen region 102a, at step
200. In the example shown in FIG. 3, the oxygen percentage is 50%.
Ventilator 10 can be operated with the set percentage of oxygen to
provide breathing gases to patient 12 at step 202.
[0065] As noted above, in order to determine the functional
residual capacity of patient 12 by a gas wash-out/wash-in
technique, it is necessary to alter the composition of the
breathing gases supplied to patient 12. To this end, the clinician
sets a different level for the oxygen content of the breathing
gases. This is performed by selecting the FRC 0.sub.2 field 206 in
menu portion 68 of screen 102g1 and appropriately establishing the
FRC 0.sub.2 value. The amount of change may be an increase or
decrease from the previously set level established at step 200;
however it must be an amount sufficient to perform the functional
residual capacity analysis. A change of at least 10% is preferable
in order to obtain an accurate indication of the functional
residual capacity. To ensure that appropriate oxygen concentrations
are supplied to patient 12 it is usually desired to increase the
oxygen level and, unless the current oxygen level is very high
(greater than 90%), a default setting of a 10% increase over the
current setting may be provided. The level of oxygen set by the
clinician "tracks" changes made in the oxygen content of the
breathing gases at the ventilator, as for example by actuating
button 104a. Thus, for example, if the ventilator oxygen is
originally 50% as shown in FIG. 3, and the FRC 02 shown in FIG. 5
is 60%, if the ventilator oxygen setting is later changed to 70%,
the FRC 02 amount will automatically move to 80%. Lowering the
ventilator oxygen setting, however, will not result in lowering the
FRC 02 amount, thereby avoiding the possibility of low oxygen
breathing gases for the patient. The alteration of the oxygen
content of the breathing gases is carried out in step 208 of FIG.
7. For exemplary purposes, below, an alteration in the form of an
increase to 75% O.sub.2 is shown in FIG. 5.
[0066] Next, the clinician must select the frequency, or interval,
at which the functional residual capacity measurements will be
carried out. This is performed at step 210. A single functional
residual capacity determination by the present method may be
selected by the appropriate field 212 in menu 68. Alternatively, a
series of FRC determinations or cycles may be selected, with a
series interval, set in field 214, between each determination. The
interval may be between one and twelve hours in increments of one
hour. The time when the next functional residual capacity
determination begins is shown in field 215.
[0067] Alternatively, functional residual capacity measurements can
be set to occur automatically in conjunction with certain
procedures controlled by ventilator 10, such as immediately prior
and/or after a period of nebulized drug therapy, recruitment
maneuvers, a suction procedure, or a change in ventilator setting.
Functional residual capacity measurement may be initiated,
terminated, delayed, interrupted, or prevented in accordance with
the occurrence of events, such as those noted above, that may
affect the accuracy of the functional residual capacity
measurement. For example, a functional residual capacity
measurement may be terminated for a high oxygen procedure for
patient 12 and then resumed or started after a "lock out"
period.
[0068] The initial or base line amount of nitrogen in the expired
breathing gases is determined at step 216. As noted above this may
be determined by subtracting the amounts of oxygen and carbon
dioxide, as determined by gas analyzer 70, from the total amount of
the breathing gases, as determined using flow sensor 62.
[0069] While the present invention is described using nitrogen as
the inert gas, it will be appreciated that other inert gas may also
be used. For example, the breathing gases for patient 12 may
include the inert gas helium and amounts of helium expired by the
patient could be used in a functional residual capacity measure in
the manner described herein.
[0070] To commence the determination of functional residual
capacity, breathing gases having the increased amount of oxygen
shown in data field 105 are provided to patient 12 in step 218. The
increased percentage of oxygen in the breathing gases will wash a
portion of the nitrogen or other inert gas out of lungs 38 of
patient 12 with each breath of the patient. The amount of breathing
gases inspired and expired by patient 12 with each breath, i.e. the
tidal volume, is a lung volume that is in addition to the residual
volume of the lungs found after expiration. The tidal volume is
also smaller than the residual volume. For a healthy adult a
typical tidal volume is 400-700 ml whereas the residual volume or
functional residual capacity is about 2000 ml. Therefore, only a
portion of the nitrogen in the lungs 38 of patient 12 is replaced
by the increased amount of oxygen with each breath.
[0071] The amount of nitrogen washed out of the lungs in each
breath is determined by subtracting the amount of oxygen and carbon
dioxide from the amount of breathing gases expired by patient 12
during each breath obtained using flow sensor 68. See step 220.
Knowing the amount of expired breathing gases, the initial amount
of expired nitrogen and the amount expired in each expiration by
patient 12, a functional residual capacity quantity can be
determined for each successive breath in steps 222a, 222b . . .
222n. Any inert gas wash out/wash in functional residual capacity
measurement technique may be used, a suitable technique for
determining functional residual capacity for use in the present
invention being described in U.S. Pat. No. 6,139,506.
[0072] The functional residual capacity quantity as determined
after each successive breath, will tend to increase as nitrogen
continues to be washed out of the lungs of the patient by the
increased oxygen in the breathing gases. This results from the fact
that the breathing gases that are inspired by patient 12, i.e., the
tidal volume, are not fully equilibrated inside the entire
functional residual capacity volume before being exhaled by the
patient. In particular, functional residual capacity volume that
lies behind intrinsic lung resistance does not mix as quickly with
inspired gases compared to functional residual capacity volume that
is pneumatically connected to the trachea through a lower
resistance path. As such, the magnitude of breath-to-breath
increases in functional residual capacity that are noted are an
indication of the amount of intrinsic resistance within the lung
gas transfer pathways. Thought of another way, additional
functional residual capacity volume that is registered many breaths
into the functional residual capacity measurement procedure is lung
volume that is not participating well in the gas transfer
process.
[0073] As the determination of functional residual capacity
proceeds, the determined values for functional residual capacity
for the breaths are displayed in graphic portion 110 of screen
102g2 as a capacity or volume curve 224 in steps 226a, 226b . . .
226c at the end of the determination for each breath. This confirms
to the clinician that the determination of functional residual
capacity is working properly. Also, as curve 224 forms from left to
right, the shape of the curve is an indication to the clinician of
the intrinsic resistance and quality of ventilation of lung
functional residual capacity, as discussed above. In the example
shown, the clinician can appreciate that patient 12 has a
homogeneously ventilated lung volume, as indicated by the
qualitative flatness of the functional residual capacity curve,
with a lung capacity of about 2500 ml.
[0074] The scaling of graph 110 of FIG. 5 may be automatically
altered to provide a scale appropriate to the functional residual
capacity data being shown.
[0075] It will be appreciated that, if desired, the data relating
breath number to the corresponding functional residual capacity
value can also be displayed in tabular form in portion 112 of
display portion 102g. This could comprise a column containing the
breath numbers and a column containing the corresponding functional
residual capacity values.
[0076] Mechanical ventilator 10 continues to supply breathing gases
having increased oxygen concentration for x number of breaths, for
example, 20 breaths. A final value for functional residual capacity
is determined at the end of the x breaths at step 228 and volume or
capacity curve 224 extends to this breath to show the final
determination of functional residual capacity at the end of 20
breaths. The functional residual capacity measurement may conclude
earlier if sufficient stability of breath-to-breath functional
residual capacity is found in curve 224.
[0077] Thereafter, at step 230 the concentration of oxygen in the
breathing gases is altered to the original level of, for example
50%, set at step 208 and ventilator 10 is operated at step 232 to
repeat steps 216-228 to make a second determination of functional
residual capacity with this alteration of the oxygen concentration
in the breathing gases. It will be appreciated that this
determination uses a wash-in of nitrogen, rather than a wash-out.
This second determination is graphed and displayed in graphic
portion 110 as graph 234, in the same manner as graph 224,
described above. The values for the two final functional residual
capacity determinations are shown in data field 237 of tabular
portion 112 of screen 102g2 in step 236. In the example shown,
these values are 2500 and 2550 ml.
[0078] For future use, the final determination of functional
residual capacity made in step 232 is compared to that determined
in step 228. This is carried out at step 238. It is then
determined, in step 240, whether the difference between the two
determinations of functional residual capacity is less or greater
than some amount, such as 25%. If the difference is less than 25%,
the two values are averaged and will be subsequently displayed in
text form in data field 245 in step 244 when determination becomes
part of the chronological record following a later functional
residual capacity determination.
[0079] If the difference between the two values for the functional
residual capacity is greater than some amount, such as than 25%,
both the final value determined at step 228 and the final value
determined in step 232 will be displayed by step 246 in data field
245 of FIG. 5 and in the graph 110. This display of the functional
residual capacity determination informs the clinician that the
accuracy of the functional residual capacity determination is
questionable.
[0080] The final value(s) for the functional residual capacity are
preferably displayed in tabular portion 112 of screen 102g2 along
with additional associated data such as the time and date at which
functional residual capacity was determined, or the values of PEEPe
and PEEPi existing when the functional residual capacity
determination was made. PEEPe is the end expiratory pressure
established by ventilator 10. PEEPi, also known as auto PEEP, is
the intrinsic end expiratory pressure and is a measurement in
pressure of the volume of gas trapped in the lungs at the end of
expiration to the PEEPe level.
[0081] While the determination of functional residual capacity has
been described as being carried out for a given number of breaths,
such as 20, it can be terminated sooner if it is apparent that the
functional residual capacity measurement has become stable on a
breath-to-breath basis. This can be conveniently determined by
measuring the O.sub.2 content of the expired breathing gases at the
end of the patient's expirations, that is, the end tidal oxygen
level. When the amount of oxygen in the expired breathing gases
attains and remains at the altered level, it is an indication that
the wash out/wash in the inert gas is complete and that the
functional residual capacity determination can be terminated.
[0082] Thereafter, if a series of functional residual capacity
determinations has been selected at step 210, steps 218 through 246
are repeated after the time interval indicated in data field 214
with the start of the functional residual capacity determination
occurring at the time displayed in data field 248. The
predetermined time interval may be overridden or the functional
residual capacity determination terminated by appropriate commands
from the clinician entered into menu 68.
[0083] The volume curves, such as 224, 234, and functional residual
capacity data, such as that in field 237, generated in the course
of successive functional residual capacity determinations are saved
by ventilator display unit 76 and, as such, can be compared to data
from previous or subsequent functional residual capacity
determinations. This comparison requires that a previous
determination of functional residual capacity be selected as a
reference curve using the time at which it was obtained as
identified in data field 250. When a reference curve is selected,
an indication is made in data field 250 and that functional
residual capacity curve is displayed as the reference curve 252.
Curve 252 shows a lung that is not well ventilated. Further
indication of the reference curve and reference curve values may be
made by a color indication for this data, different from that of
the other functional residual capacity data in graph 110 and table
112. The result is a visual indicator that can easily be referred
to by the clinician to quickly assess improvement or deterioration
in the functional residual capacity condition of patient 12 over
time. In the example shown in FIG. 5, there has been an increase in
the functional residual capacity of patient 12 for each eight hour
interval.
[0084] Also, it is common practice to alter, usually increase, the
PEEP to improve ventilation of lungs 38 of patient 12 by opening
areas of the lung that are not being properly ventilated.
Tabulating the actual measured values for PEEPe and PEEPi, along
with the corresponding functional residual capacity determination,
as shown in FIG. 5, allows the clinician to see the effect, if any
of applied PEEPe therapy on the volume of the functional residual
capacity of the patient's lungs, as well as on the intrinsic PEEP.
As also shown in FIG. 5, a history of a certain number of
functional residual capacity determinations and PEEP pressures are
shown in display region 70 to present trends and the history of
these quantities. In the example shown there, an increase in PEEPe
has resulted in an increase in functional residual capacity of
patient 12.
FRC Events Log
[0085] Certain clinical or other events can affect the value for
functional residual capacity determined from the method steps shown
in FIG. 7. Such events may include performing a suction routine on
patient 12 to remove accumulated secretions, administering a
nebulized medication, changing the ventilation mode, or changing
one or more ventilation parameters, such as tidal volume (TV),
breath rate, PEEP, or other parameter.
[0086] By selecting the FRC Log field 252 in menu 68 of screen
102g2 shown in FIG. 5, screen 102g4 of FIG. 8 will be shown to
provide a log of the events that may effect functional residual
capacity in data field 254 along with the time(s) and date(s) the
event took place. The log also includes the time, date and value of
any periodic functional residual capacity determinations made in
the manner described above. The clinician may scroll through the
events of the log using control knob 106 to review the functional
residual capacity event history in relation to the measured values
of functional residual capacity to determine if specific actions
had a positive or negative effect on the determined functional
residual capacity for the patient.
PEEP Determination and Display
[0087] An aspect of the present invention allows the clinician to
ascertain the relationship between the functional residual capacity
of patient 12, and PEEP applied to the patient, thereby to assist
the clinician in establishing a PEEP level deemed optimal for
patient 12. An optimal PEEP level, in the present context, is one
beyond which diminishing functional residual capacity increases in
association with PEEP increases is noted. The PEEP INview screen
102g5 of FIG. 9 may be used for this purpose. For screen 102g5, a
series of periodic functional residual capacity determinations is
made, preferably in the manner shown in FIG. 7, with each
determination being at a different incremented level of PEEP. For
this purpose, in menu 108, the clinician sets an altered
concentration of oxygen to be used in the functional residual
capacity determination in data field 400. The clinician also enters
an initial PEEP value at data field 402 and an end PEEP value at
data field 404. The initial PEEP value may be low and the end value
high, as shown in FIG. 9, or the initial value high and the end
value low. The clinician also sets the number of functional
residual capacity measurements to be made between the initial and
end PEEP values in data field 406. In the example shown in FIG. 9,
five such measurements are to be made. In an alternative
embodiment, the incremental PEEP associated with each measurement,
for example an incremental change of 3 cmH.sub.2O for each
measurement, may be set. While use of the method of determining
functional residual capacity of FIG. 7 is described below, it will
be appreciated, that for the purpose of determining a suitable
PEEP, any method of determining functional residual capacity may be
employed.
[0088] The series of measurements of functional residual capacity
starting at the initial value of PEEP and incrementally moving to
the end value of PEEP is then performed as in a manner of steps
216-228 or steps 216-246 shown in FIG. 7. These functional residual
capacity determinations are graphically displayed in graph 110 of
FIG. 9 as points/curve 408. Graph 110 of screen 102g5 has
functional residual capacity on the ordinate and PEEP on the
abscissa. The corresponding numeric functional residual capacity
data is displayed in table 112 that contains the functional
residual capacity values and the PEEP values at which that
functional residual capacity value was obtained.
[0089] Curve 408 and table 112 provide guidance to the clinician in
selecting a PEEP level for ventilating patient 12. For example,
from the graph and table of FIG. 9 it can be seen that increasing
the PEEP from 2 to 6 cmH.sub.2O increases functional residual
capacity by 500 ml whereas increasing PEEP beyond 6 cmH.sub.2O
provides a relatively small increase in functional residual
capacity. This suggests to the clinician that 6 cmH.sub.2O would be
an appropriate PEEP for the patient.
[0090] Curve 408 can be saved in a memory in ventilator 10 or
display unit 76. If ventilator settings are not changed or are not
changed in any significant way, curves 408 obtained at different
times in the course of the patient's treatment can be usefully
presented in graphic portion 110 of screen 102gto enable the
clinician to note changes in the PEEP curve over time by comparing
the data of two or more curves 408 over time.
[0091] Also, while the foregoing has described obtaining and
presenting a graph and table of functional residual capacity and
PEEP, other aspects of the ventilation of patient 12 by ventilator
10 may affect the functional residual capacity. For example, the
respiration rate, or the related quantities of expiration time and
inspiratory:expiratory (I:E) ratio, can affect functional residual
capacity primarily through the mechanism of intrinsic PEEP.
Determining and displaying the relationship of one or more of these
quantities to functional residual capacity may be useful to a
clinician. To this end, the functional residual capacity of the
lungs 38 of patient 12 can be determined at differing respiration
rates and the data displayed in graphic or tabular form to show the
relationship between functional residual capacity and respiration
rate. In graphic portion 110, the abscissa would show the
respiration rate while the abscissa continues to show functional
residual capacity. A tabular presentation comprises a column of
respiration rates and a column of corresponding functional residual
capacity determinations.
[0092] FIG. 9B shows an example of a further manner of obtaining
and displaying functional residual capacity and PEEP data. In FIG.
9B, the abscissa presents PEEP and the ordinate presents the change
in functional residual capacity volume for a given change in PEEP,
or .DELTA.FRC/.DELTA.PEEP.
[0093] The relationship between changes in lung volume and changes
in lung pressure is termed the "compliance" of the lung. As a
general expression of lung characteristics, it describes the
elasticity or "stiffness" of the lungs. Lungs of high compliance
are elastic and a large change in volume occurs for a small change
in pressure. The reverse is true for a stiff lung. Some lung
conditions decrease lung compliance. Others, such as emphysema,
increase lung compliance.
[0094] In the present context, the presentation of changes in
functional residual capacity volume, .DELTA.FRC, to changes in
PEEP, .DELTA.PEEP, in FIG. 9B as compliance properties of the lung
serves to emphasize clinically important data presented in graphic
and textual form in FIG. 9 and to aid the clinician in selecting an
appropriate PEEP for the patient. For this purpose, the ordinate of
graph 110 in FIG. 9B is labeled as compliance. The data in FIG. 9
presented in the manner of FIG. 9B shows that the incremental 2
cmH.sub.2O pressure increase in PEEP from 2 to 4 cmH.sub.2O PEEP
produced a functional residual capacity volume increase of 200 ml,
giving a compliance of 100 ml/cmH.sub.2O, as graphically shown in
FIG. 9B at the left hand point in the graph. In the same manner,
the incremental 2 cmH.sub.2O PEEP increase from 4 to 6 cmH.sub.2O
PEEP produced a functional residual capacity volume increase of 300
ml, giving a compliance of 150 ml/cmH.sub.2O at the second point,
proceeding to the right in the graph of FIG. 9B. Corresponding
determinations are made for the incremental PEEP increases from 6
to 8 and from 8 to 10 cmH.sub.2O and shown by the remaining points
in FIG. 9B. The data may also be presented in tabular form in table
112 of FIG. 9B.
[0095] The peak in the graph of FIG. 9B suggests to the clinician
that a PEEP of 6 cmH.sub.2O would be advantageous for the
patient.
Recruitment /De-recruitment of Lung Volume
[0096] While screen 102g5 of FIG. 9 provides valuable insight and
information to the clinician, it may also be helpful for the
clinician to have a better idea of how much of an increase in
functional residual capacity is due to distension of the lung by
increased PEEP and how much is due to making previously closed
alveolar sacs available, i.e., opening of the lung by "recruitment"
of lung volume.
[0097] One way such information may be obtained using the PEEP
INview screen 102g5 of FIG. 9 is as follows. Functional residual
capacity is determined for a series of PEEPs, in the manner
described above to produce a curve, such as curve 408. Thereafter a
recruitment maneuver is carried out on patient 12 to open the
alveolar sacs of the lungs of the patient. This would ordinarily be
the provision of a high level of PEEP that, while it may only be
tolerated by a patient for a short period of time, serves to open
the alveolar sacs of the patient lungs. This is ordinarily carried
out by the clinician by operating ventilator 10 independently of
screen 102g5. For this maneuver, it is preferable to use a
recruitment PEEP greater than the highest PEEP set in menu 108 of
screen 102g5 to ensure the alveolar sacs open.
[0098] After the recruitment maneuver has been completed, the
functional residual capacity is again determined for the same
series of PEEPs used prior to performing the recruitment maneuver
to produce another curve 408a. The two curves can be displayed in
graphic portion 110 of screen 102g5 in the manner shown in FIG. 9A.
If the recruitment maneuver resulted in the recruitment of lung
volume, i.e. in the opening of previously closed alveolar sacs,
curve 408a will show a higher functional residual capacity than
curve 408, as shown in FIG. 9A. Curves 408 and 408a will tend to
come together at the PEEP level at which de-recruitment of lung
volume begins to occur. This suggests to the clinician that a PEEP
level greater than one at which de-recruitment begins to occur
would be appropriate for the patient.
[0099] Another way such information can be obtained using the
spirometry aspects of the present invention, as shown in the SpiroD
screen 102g3 of FIG. 10 and, particularly, the lung INview screen
102g6 of FIG. 12.
[0100] In general, spirometry is used to determine the mechanics of
a patient's lungs by examining relationships between breathing gas
flows, volumes, and pressures during a breath of a patient. A
commonly used relationship is that between inspired/expired
breathing gas flows and volumes that, when graphed, produces a loop
spirogram. The size and shape of the loop is used to diagnose the
condition of the lung.
[0101] A relationship also exists between inspired/expired gas
volumes and pressure in the lungs. In the past, a problem with the
use of this relationship has been that pressure has been measured
at a point removed from the lungs so that the measured pressure may
not be an accurate reflection of actual pressure in the lungs thus
lessening the diagnostic value of the pressure-volume loop. Through
the use of catheter 94 extending from endotracheal tube 90 shown in
FIG. 2, a far more accurate indication of lung pressure is
obtained. For a healthy lung, a graph of the relationship between
volume and pressure is roughly an elongated, narrow loop of
positive uniform slope. That is, constant increments of inspired
volume increase lung pressure by constant increments. The loop is
formed because there remains some amount of lung resistance below
the pressure sensing point at the end of catheter 94. In a diseased
lung, the loop may be wider and may also reflect a non-linear lung
volume pressure relationship. For such a lung, the volume-pressure
relationship over the course of an inspiration/expiration may be in
a form such as that shown in FIG. 10 by 420, and a curve
illustrating the volume-pressure relationship resulting from a
mathematical computation using loop data is plotted, as shown in
FIG. 10 by reference numeral 422. The curve 422 shown in FIG. 10 in
often termed a "dynostatic curve" and is used for diagnostic
purposes. A typical dynostatic curve is shown in FIG. 10 to contain
a middle portion of somewhat linear positive slope and a pair of
inflection points separating end portions of differing slopes. The
dynostatic curve and its generation is described in Practical
Assessment of Respiratory Mechanics by Ola Stenqvist, British
Journal of Anesthesia 91(1), pp. 92-105 (2003) and "The Dynostatic
Algorithm in Adult and Paediatric Respiratory Monitoring"by Soren
Sondergaard, Thesis, University Hospital, Gothenburg University,
Sweden (2002).
[0102] In graph 110 of FIG. 10, the abscissa of the graph is lung
pressure measured at the end of catheter 94 connected to the
auxiliary input A of ventilator display unit 76 and is termed
"Paux". The ordinate is scaled in volume of breathing gases
inspired/expired by patient 12. It will be appreciated that this
volume comprises the tidal volume for the patient. The tidal volume
moves into and out of the lungs in a manner that can be described
as being "above" the functional residual capacity. That is, for
normal breathing, a patient starts a breath with the volume of the
lungs at the functional residual capacity which may, for example be
2000 ml. During inhalation, the volume of the lungs increases by
the tidal volume of, for example 500-700 ml, and during exhalation,
the volume of the lungs decreases by approximately that amount. The
same situation occurs when a patient is being provided with
breathing gases from a mechanical ventilator, such as ventilator
10. It must thus be appreciated that the ordinate of the graph 110
in FIG. 10 is scaled in the relative volume of
inspiration/expiration for which the origin of the graph is zero,
not in absolute volume that would also take into consideration
functional residual capacity and for which the origin of a graph
would be the amount of the functional residual capacity. The
scaling of graph 110 of FIG. 10 may be automatically altered to
provide a scale appropriate to the spirometry data being shown.
[0103] With PEEP applied to patient 12 by ventilator 10, there will
be a movement of the graph away from the origin of the axes along
the abscissa. The graph will move right by the amount of the PEEP,
i.e. the lung pressure at the end of expiration by patient 12.
[0104] The menu portion 108 of SpiroD screen 102g3 shown in FIG. 10
allows the user to open up a set up menu, shown in FIG. 11 that
allows the clinician to turn a purge flow through catheter 94 on or
off or to zero the Paux sensor connected to catheter 94 when the
purge flow is on and endotracheal tube 90 has been inserted in
patient 12. The SpiroD set-up menu also allows the clinician to set
the scaling for the graphical portions of the display. A "Paux
Alarm" screen, reached from the SpiroD setup screen of FIG. 11,
allows the clinician to set appropriate alarms for patient lung
pressure, as sensed by catheter 94.
[0105] Various other selections on menu 108 of screen 102g3 of FIG.
10 allow the clinician to save the current data and to view this
information as a first or second reference for use and display with
subsequently obtained data. Up to a given number of loops, for
example, six loops and curves, may be saved for analytical
purposes. The "erase reference" option allows the user to determine
which information to save and which to delete.
[0106] The "SpiroD loops" and "SpiroD curves" menu items may be
turned on or off. Selecting "on" for both the curve and loop will
display both the loop and the curve at once in the manner shown in
FIG. 10. For easier comparison among loops and curves obtained at
various times, either the loop or curve showing may be turned
"off." The "cursor" option allows the clinician to scroll along the
horizontal axis and display the actual pressure and volume
measurements associated with the loops or curves that are
displayed.
[0107] For the graphical showing of graph 110 of the screen 102g3
in FIG. 10, volumes and pressures are obtained from sensor 57 and
catheter 94 and the spirometry data, computed and displayed for
every third breath if the respiratory rate is less than some
desired number, for example, 15 breaths per minute. If the
respiratory rate is greater than that number, every fifth breath
used. The loop 420 for a complete inspiratory/expiratory breathing
cycle is displayed in the graph of screen 102g3 of FIG. 10. The
dynostatic curve 422 is then calculated for display in graph
110.
[0108] Various compliance values for the patient's lungs are shown
in the table 112 of screen 102g3 of FIG. 10. Compliance can be seen
as the amount by which the volume of the lung increases for an
incremental increase in lung pressure. The data necessary to
determine compliance can be obtained from sensor 57 and gas module
64. Compliance is represented by the slope of dynostatic curve 422.
It is an indication of the stiffness or elasticity of the lung. In
a stiff lung, an incremental increase in pressure results in a
smaller increase in volume over a lung that is more elastic and the
slope of curve 422 is more horizontal. In an elastic lung, the
reverse is true. To aid the clinician in analyzing the lungs of
patient 10, the compliance is computed at the beginning, middle,
and end of the respiratory cycle of the patient. As shown in the
example in FIG. 10, the middle portion of dynostatic curve 422
indicates a portion of greater compliance than the end portions.
This is reflected in the greater slope of the middle portion over
those of the end portions. The table of the screen sets out
numerical values. Ordinarily, the highly compliant, middle portion
of curve 422 shown in FIG. 10 is that in which the lung is most
effectively ventilated.
[0109] The table 112 of display 102g3 of FIG. 10 also shows the
peak pressure achieved in the lungs during the breath, the PEEP
pressure, and the airway resistance, Raw. The airway resistance is
the pressure drop experienced by breathing gas flow of the lungs
and is expressed in units of pressure per unit of flow. Airway
resistance can also be determined with data from sensor 57 and gas
module 64 in a manner described in the Stenqvist reference noted
above.
[0110] The present invention provides a unique way of viewing the
relationship among functional residual capacity, PEEP, and
recruited:de-recruited lung volume that is deemed helpful in
enabling a clinician to determine a suitable value for PEEP. To
carry this out, the PEEP INview screen 102g5 shown in FIG. 9 is
reached. Among the menu items present in PEEP INview screen 102g5
is "Lung INview on/off" in field 424. When "Lung INview" is turned
"on" a screen 102g6 in the format of FIGS. 12a and 12b is present
in ventilator display unit 76. As shown in FIG. 4, the PEEP INview
screen 102g6 of FIG. 9 can be reached either via the FRC INview
display 102g2 described above and shown in FIG. 5 at field 426 or
the SpiroD display 102g3 shown in FIG. 10 at field 428. When the
former route is chosen to reach the PEEP INview screen of FIG. 9,
the spirometry data described above will still be obtained and
calculated in ventilator display unit 76 but the screen of FIG. 10
will not be displayed in the display unit.
[0111] To proceed with the Lung INview display, in the PEEP INview
screen 102g5 shown in FIG. 9, the menu item "Lung INview on/off"
424 is toggled "on" and the ventilator display unit will show
screen 102g6 in the format of FIGS. 12a and 12b.
[0112] For an embodiment of the invention using a wash in/wash out
determination of functional residual capacity, in field 430 of menu
108 of display 102g6 of FIG. 12a/b, the clinician sets the altered
oxygen level to be used in the functional residual capacity
measurement employed to produce the Lung INview data. To begin the
process of providing data for display 102g6, the clinician
establishes initial and end PEEPs values at fields 432 and 434, as
well as the number of measurements to be taken within the range of
PEEP so established at field 436, in the same general manner as
described above in connection with the PEEP INview display 102g5 of
FIG. 9. Alternatively, and if desired, field 436 can show the
incremental/decremental PEEP step, for example a step of 3
cmH.sub.2O. In the example shown in FIG. 12, the initial PEEP is 25
cmH.sub.2O, the end PEEP is 5 cmH.sub.2O, and five measurements
will be taken within that range of PEEP, namely measurements at 25,
20, 15, 10, and 5 cmH.sub.2O of PEEP. It is deemed preferable to
initiate the process of determining the optimal PEEP by using the
highest value of the selected range and thereafter decrementing the
applied PEEP to the lower end level. However, as noted in
connection with the description of screen 102g5 of FIG. 9, the
invention can also be practiced with incrementing PEEP from a low
value to a high value, depending on the preference of the
clinician.
[0113] The graph 110 of screen 102g6 of FIG. 12 has the abscissa
scaled in PEEP and the ordinate scaled in functional residual
capacity. The table 112 of screen 102g6 provides columns for the
set PEEP, functional residual capacity and airway resistance (Raw).
The table also includes a column for "difference" that, as
hereinafter described, contains a numerical indication of the lung
volume that is recruited/de-recruited in the lungs as the PEEP is
incremented/decremented.
[0114] As shown in FIG. 13, at step 500, a recruitment maneuver is
preferably run on patient 12 to open the lungs of the patient. As
noted above, such recruitment maneuver would typically be the
provision of a high level of PEEP opens the alveolar sacs of the
patient lungs. It is preferable to use a recruitment PEEP greater
than the highest PEEP set in menu 108 of screen 102g6 to ensure the
alveolar sacs open. In step 502, the functional residual capacity
and PEEP parameters are established in menu 108 of display 102g6,
shown in FIG. 12, as previously described. Step 502 may occur
before step 500 reversing the order shown in FIG. 13. Thereafter,
in step 504, the patient is ventilated by ventilator 10 with the
PEEP at the initial level found in the menu. In the present
exemplary instance, patient 12 is initially ventilated with a PEEP
of 25 cmH.sub.2O in step 504.
[0115] In step 506, the functional residual capacity of patient 12
is determined by the wash in/wash out technique using the altered
oxygen concentration level as described above in connection with
FIGS. 5 and 7 or using some other appropriate technique for
measuring functional residual capacity. The determined value is
graphically displayed in graph 110 at the corresponding value of
PEEP as point 508. The values are also entered in tabular form in
table 112 of screen 102g6 of FIG. 12.
[0116] Next, the PEEP pressure is altered to the next decremental
level, in the present instance from 25 cmH.sub.2O to 20 cmH.sub.2O,
and the patient is ventilated at the new PEEP level in step 510. In
step 512, the functional residual capacity is again determined and
displayed with respect to PEEP in the same manner as in step 506 at
point 514. Curve 516 is formed in graph 110 from points 508 and
514.
[0117] A dynostatic curve is also obtained for the ventilation of
the patient's lungs at the PEEP of 20 cmH.sub.2O. FIG. 14 shows the
spirometry data obtained at step 518 for the PEEP of 20 cmH.sub.2O.
For ease of explanation, the spirometry loop is shown simply as an
ellipse 520 and dynostatic curve 522 shown as a straight line, it
being understood that the spirometry loops and curves will actually
resemble those shown in FIG. 10. However, the ordinate of the graph
of FIG. 14 is scaled in absolute volume, not the relative volume of
FIG. 10, so as to show functional residual capacity, as noted in
steps 506 and 512.
[0118] The origin for dynostatic curve 522 will be the PEEP value
of 20 cmH.sub.2O and the associated functional residual capacity
value so that the origin corresponds to point 514 of FIG. 12 and
FIG. 14. FIG. 14 can be seen as an enlargement of FIG. 12 showing
the data used to generate the data of FIG. 12 and also showing
dynostatic loops and curves. FIG. 14 shows a significant amount of
data relating to the condition of the lungs of patient 12. The
graph 110 of screen 102g6 of FIG. 12 shows the salient features of
that data, thereby to assist and facilitate the selection of an
optimal PEEP for patient 12 by the clinician.
[0119] Steps 510, 512 and 518 are then repeated for the next
decremented PEEP of 15 cmH.sub.2O. This produces a new point 530 of
functional residual capacity and PEEP in curve 516 in FIGS. 12a and
12b and in FIG. 14. It also produces a new spirometry loop and
dynostatic curve 532. Steps 510, 512, and 518 are again repeated
for a PEEP of 10 cmH.sub.2O to produce point 534 and dynostatic
curve 536 shown in FIG. 14.
[0120] Steps 524, 526 and 528 are used to determine the amount of
recruited or de-recruited volume obtained in the lungs of patient
12. At PEEPs of 15 and 10 cmH.sub.2O, some de-recruitment of lung
volume is noted and steps 524, 526 and 528 of FIG. 13 are explained
in conjunction with these PEEPs. In step 524 and using the
dynostatic curve 536 for the reduced PEEP of 10 cmH.sub.2O, the
volume of the lungs at a pressure corresponding to that of the
previous PEEP of 15 cmH.sub.2O is determined. Graphically, this may
be accomplished by establishing vertical line 538 in of FIG. 14 at
the previous PEEP of 15 cmH.sub.2O and noting the intersection of
line 538 and dynostatic curve 536 at point 540.
[0121] The amount of volume on the ordinate scale represented by
the line segment 538a between points 530 and 540 is also
determined. In the present instance, this amounts to approximately
180 ml. In step 528, this value is placed in table 112 of screen
102g6 in association with the previous PEEP of 15 cmH.sub.2O. In
step 526, point 540 is placed in graph 110 of screen 102g5 as shown
in FIGS. 12a and 12b.
[0122] FIG. 12b shows the completed Lung INview process, including
the final measurement of functional residual capacity at a PEEP of
5 cmH.sub.2O. This is carried out by repeating steps 510, 512, and
518, for a PEEP of 5 cmH.sub.2O to produce plot 542 of functional
residual capacity and PEEP and dynostatic curve 544. Repeating
steps 524, 526, and 528 produces point 546 and line segment 548a
representing a volume of about 120 ml. The data is displayed in a
manner corresponding to that described above in graph 110 and table
112 of screen 102g6. As the determination of the "difference"
requires both functional residual capacity measurement taken at a
previous PEEP and a dynostatic curve from subsequent PEEP and is
referenced to the previous PEEP, no difference value will appear in
the graph and table of screen 102g6 of FIG. 12b for the 5
cmH.sub.2O level of PEEP.
[0123] Reverting now to the situation with respect to the PEEPs of
25 and 20 cmH.sub.2O, as noted above, at these higher PEEPs, there
is little de-recruitment of lung volume as the alveolar sacs are
continuously open during the respiratory cycle. This is expressed
in FIG. 14 by the fact that dynostatic curve 522 for a PEEP of 20
cmH.sub.2O passes through point 508 formed using the functional
residual capacity for a PEEP of 25 cmH.sub.2O. Thus, no difference
of the type represented by lines 538a and 548a will be seen when
the PEEP is reduced from 25 cmH.sub.2O to 20 cmH.sub.2O . This fact
is shown as 0 difference in table 112 for a PEEP of 25 cmH.sub.2O,
since, as noted at step 528, the difference is tabulated to the
previous PEEP.
[0124] An analogous situation exists for dynostatic curve 532
generated for the PEEP of 15 cmH.sub.2O. That is, dynostatic curve
532 passes through point 514 formed using the functional residual
capacity for 20 cmH.sub.2O. Again, there is a zero difference as
tabulated in table 112 for 20 cmH.sub.2O. In graph 110 of FIGS. 12a
and 12b, where the difference approximates zero, the differences
determined in step 528 and the plot of the functional residual
capacity at the previous PEEP are roughly the same and
overlapping.
[0125] However, as the PEEP is further decremented, de-recruitment
of lung volume begins to occur. For example, point 530 shows that
for a PEEP of 15 cmH.sub.2O, when the lung pressure is at that
level, the lung volume is about 1800 ml. But when the PEEP is
lowered to 10 cmH.sub.2O, for a pressure in the lungs of 15
cmH.sub.2O, the lung volume is only about 1620 ml, as evidenced by
the plot of point 540. There has thus been a lung volume
de-recruitment of approximately 180 ml when the PEEP was lowered
from 15 cmH.sub.2O to 10 cmH.sub.2O, as evidenced by the length of
line segment 538a.
[0126] An analogous situation exists when the PEEP is lowered from
10 cmH.sub.2O to 5 cmH.sub.2O as shown by line segment 548a. The
de-recruitment of lung volume in that case is about 120 ml.
[0127] It will be appreciated, that a clinician may readily discern
an optimal PEEP for patient 12 from the graphic and tabular data
provided in screen 102g6 of FIG. 12b. Right after the recruitment
maneuver of step 500, and for the higher PEEPs of 25 and 20
cmH.sub.2O, the alveolar sacs will remain generally open during
breathing due to the higher pressures. While this is advantageous
from the standpoint of lung volume, the high pressure may be
injurious to the patient. There is little reduction, or
de-recruitment of lung volume as expiration proceeds to the end
expiratory pressure, as shown in FIG. 12.
[0128] As PEEP is further reduced to 15 cmH.sub.2O and then to 10
cmH.sub.2O, a difference in volume will occur and curve 548 will
separate below curve 516 in graph 110. The clinician will be able
to note that at a PEEP of 10 cmH.sub.2O, a portion of the lung
volume that had been open at a PEEP of 15 cmH.sub.2O will remain
closed as pressure is increased from the PEEP of 10 cmH.sub.2O to
15 cmH.sub.2O during the course of inspiration while moving up the
dynostatic curve. This difference, 180 ml in the example shown in
FIGS. 12a and 12b and line segment 538a of FIG. 14, represents the
"de-recruitment" of lung volume as the PEEP was reduced from 15
cmH.sub.2O to 10 cmH.sub.2O. Conversely, a volume would be
"recruited" if the PEEP was increased from 10 cmH.sub.2O to 15
cmH.sub.2O.
[0129] Further lowering the PEEP to 5 cmH.sub.2O results in an
additional de-recruited loss of lung volume of 120 ml as shown by
line segment 548a. As can be seen from the graph, the lung begins
to lose volume or "derecruits" at PEEP settings below 15 cmH.sub.2O
and this suggests that 15 cmH.sub.2O is a PEEP that is best suited
or optimal for patient 12. In selecting an optimal PEEP, the
clinician may set the PEEP at 15 cmH.sub.2O so as to obtain some
recruitment of lung volume over a PEEP of 10 cmH.sub.2O. This may
be preceded by a recruitment maneuver, such as at step 500, if
desired. Or, the clinician may leave the PEEP at 10 cmH.sub.2O
since some recruitment is obtained at that level of PEEP.
[0130] As described above in connection with the determination of
functional residual capacity, the determination of a suitable PEEP
can be set to automatically occur in conjunction with certain
procedures carried out by ventilator 10 or treatment procedures
carried out on patient 12.
[0131] While the foregoing describes an example in which PEEP is
decreased as the amount of recruitment or de-recruitment is
determined, it will be appreciated that the technique may also be
carried out using incremented, increasing values of PEEP.
[0132] Various alternatives and embodiments are contemplated as
being within the scope of the following claims particularly
pointing out and distinctly claiming the subject matter regarded as
the invention.
* * * * *