U.S. patent application number 11/386807 was filed with the patent office on 2006-08-10 for ventilation method and control of a ventilator based on same.
Invention is credited to Nader Maher Habashi.
Application Number | 20060174884 11/386807 |
Document ID | / |
Family ID | 26872514 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060174884 |
Kind Code |
A1 |
Habashi; Nader Maher |
August 10, 2006 |
Ventilation method and control of a ventilator based on same
Abstract
The invention provides an improved ventilation method and method
for controlling a ventilator apparatus in accordance with same.
More specifically, the present invention relates to a method of
controlling a ventilator apparatus comprising the steps of placing
a ventilator in a mode capable of adjusting airway pressure (P) and
time (T), monitoring expiratory gas flow, analyzing the expiratory
gas flow over time (T) to establish an expiratory gas flow pattern,
and setting and/or adjusting a low time (T2) based on the
expiratory gas flow pattern. Alternatively, the present invention
relates to a method of controlling a ventilator apparatus
comprising the steps of placing a ventilator in a mode capable of
adjusting airway pressure (P) and time (T), and setting a low
airway pressure (P2) of substantially zero cmH.sub.2O.
Inventors: |
Habashi; Nader Maher;
(Huntersville, NC) |
Correspondence
Address: |
EPSTEIN BECKER & GREEN, P.C.
1227 25TH STREET, N.W. 7TH FLOOR
WASHINGTON
DC
20037
US
|
Family ID: |
26872514 |
Appl. No.: |
11/386807 |
Filed: |
March 23, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10176710 |
Jun 20, 2002 |
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11386807 |
Mar 23, 2006 |
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60299928 |
Jun 21, 2001 |
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Current U.S.
Class: |
128/204.21 ;
128/200.24; 128/203.12; 128/204.18; 128/204.23 |
Current CPC
Class: |
A61M 2205/3334 20130101;
A61M 2205/3331 20130101; A61M 2230/205 20130101; A61M 16/0069
20140204; A61M 2016/0039 20130101; A61M 2230/202 20130101; A61M
2205/50 20130101; A61M 16/024 20170801; A61M 2016/0042 20130101;
A61M 2016/003 20130101; A61M 16/0003 20140204 |
Class at
Publication: |
128/204.21 ;
128/200.24; 128/203.12; 128/204.18; 128/204.23 |
International
Class: |
A61M 16/00 20060101
A61M016/00; A62B 7/00 20060101 A62B007/00 |
Claims
1-14. (canceled)
15. A method of weaning from ventilation comprising the step of
substantially contemporaneously adjusting a high airway pressure
(P1) and a high time (T1).
16. The method of claim 15, wherein the adjusting step comprises
decreasing P1 and increasing T1.
17. The method of claim 16, wherein P1 is decreased at a rate of
about 2 cmH.sub.2O per hour and T1 is increased by about 0.5 to 1.0
s substantially contemporaneously with each decrease in P1.
18. The method of claim 16, wherein P1 is decreased in increments
of about 4 cmH.sub.2O and T1 is increased in increments of about 2
s.
19. The method of claim 16, further comprising the step of
transitioning ventilation from a preset continuous positive airway
pressure (CPAP) level mode with an intermittent release to a
substantially continuous positive airway pressure (CPAP) mode.
20. The method of claim 16, further comprising the step of
transitioning ventilation from a preset continuous positive airway
pressure (CPAP) level mode with an intermittent release to a
substantially continuous positive airway pressure (CPAP) mode with
automatic tube compensation (ATC).
21. The method of claim 19, further comprising the steps of: a)
monitoring blood oxygen levels, b) monitoring blood carbon dioxide
levels, c) determining the ratio of spontaneous minute ventilation
to machine minute ventilation, and d) determining the level of
sedation.
22. The method of claim 19, further comprising the steps of
substantially simultaneously decreasing machine minute ventilation
and increasing spontaneous minute ventilation to transition from
the CPAP mode to an unassisted breathing mode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/176,710 filed Jun. 20, 2002, which claims priority to U.S.
Provisional Application No. 60/299,928 filed Jun. 21, 2001.
FIELD OF THE INVENTION
[0002] The invention related to the field of ventilating human
patients. More particularly, the present invention relates to an
improved method of initiation, management and/or weaning of airway
pressure release ventilation and for controlling a ventilator in
accordance with same.
BACKGROUND OF THE INVENTION
[0003] Airway pressure release ventilation (APRV) is a mode of
ventilation believed to offer advantages as a lung protective
ventilator strategy. APRV is a form of continuous positive airway
pressure (CPAP) with an intermittent release phase from a preset
CPAP level.
[0004] During APRV, ventilation occurs on the expiratory limb. The
resultant expiratory tidal volume decreases lung volume,
eliminating the need to elevate end inspiratory pressure above the
upper inflection point. Therefore, tidal volume reduction is
unnecessary. CPAP levels can be set with the goal of optimizing
recruitment without increasing the potential for over distension.
Consequently, end inspiratory pressure can be limited despite more
complete recruitment and ventilation can be maintained.
[0005] APRV is also associated with reduction or elimination of
sedative, inotropic and neuromuscular blocking agents.
[0006] APRV is a form of positive pressure ventilation that
augments alveolar ventilation and lowers peak airway pressure.
Published data on APRV has documented airway pressure reduction on
the order of 30 to 75 percent over conventional volume and pressure
cycled ventilation during experimental and clinical studies. Such
reduction of airway pressure may reduce the risk of VILI. APRV
improves ventilation to perfusion ratio (VA/Q) matching and reduces
shunt fraction compared to conventional ventilation. Studies
performed utilizing multiple inert gas dilution and excretion
technique (MIGET) have demonstrated less shunt fraction, and dead
space ventilation. Such studies suggest that APRV is associated
with more uniform distribution inspired gas and less dead space
ventilation than conventional positive pressure ventilation.
[0007] APRV has been associated with improved hemodynamics. In a
10-year review of APRV, Calzia reported no adverse hemodynamic
effects. Several studies have documented improved cardiac output,
blood pressure and oxygen delivery. Consideration of APRV as an
alternative to pharmacological or fluid therapy in the
hemodynamically-compromised, mechanically-ventilated patient has
been recommended in several case reports.
[0008] However, most patients with ALI/ARDS exhibit expiratory flow
limitations. Expiratory flow limitations results in dynamic
hyperinflation and intrinsic positive end expiratory pressure
(PEEP) development. In addition, ARDS patients experience increased
flow resistance from external ventilator valving and gas flow path
circuitry including the endotracheal tube and the external
application of PEEP.
[0009] Several mechanisms can induce expiratory flow limitations in
ALI/ARDS. In ALI/ARDS both FRC and expiratory flow reserve is
reduced. Pulmonary edema development and superimposed pressure
result in increased airway closing volume and trapped volume. In
addition, the reduced number of functional lung units (de-recruited
lung units and enhanced airway closure) decrease expiratory flow
reserve further. Low volume ventilation promotes small airway
closure and gas trapping. In addition elevated levels of PEEP
increase expiratory flow resistance. In addition to downstream
resistance, maximal expiratory flow depends on lung volume. The
elastic recoil pressure stored in the proceeding lung inflation
determines the rate of passive lung deflation.
[0010] APRV expiratory flow is enhanced by utilization of an open
breathing system and use of low (0-5 cmH.sub.2O) end expiratory
pressure. EELV is maintained by limiting the release time and
titrated to the inflection point of the flow volume curve.
[0011] PSV required significant increases in pressure support
levels (airway pressure) to match the same minute ventilation.
[0012] Conventional lung protective strategies are associated with
increased use of sedative agents and neuromuscular blocking agents
(NMBA).
[0013] In addition to drug cost reduction, elimination of NMBA is
thought to reduce the likelihood of associated complications such
as prolonged paralysis and may facilitate weaning from mechanical
ventilation.
[0014] Mechanical ventilation remains the mainstay management for
acute respiratory failure. In contrast, shear force stress from
repetitive airway closure during the tidal cycle from mechanical
ventilation results in low volume lung injury.
[0015] End expiratory lung volume was maintained by setting PEEP
levels to 2 cmH.sub.2O above the lower inflection point.
[0016] Such important differences between these studies limited
conclusions as to the effectiveness of low tidal ventilation
limiting ventilator associated lung injury (VALI).
[0017] Recent completion of the large controlled randomized ARDSNet
trial documented improved survival and ventilator free days
utilizing low tidal volume ventilation (6 ml/kg) vs. traditional
tidal volume ventilation (12 ml/kg). although the low tidal volume
group (6 ml/kg) and traditional tidal volume group (12 ml/kg)
groups utilized identical PEEP/FiO.sub.2 scales, PEEP levels were
significantly higher in the low tidal volume group. Higher PEEP
levels were required in the low tidal volume group in order to meet
oxygenation goals of the study. Despite improved survival in the
low tidal volume group (6 ml/kg) over traditional tidal volume
group (12 ml/kg), survival was higher in the Amato study. The
ARDSNet trial also failed to demonstrate any difference in the
incidence of barotraumas. The higher PEEP requirements and the
potential for significant intrinsic PEEP from higher respiratory
frequency in the lower tidal volume group, may have obscured
potential contribution of elevated end expiratory pressure on
survival. Further studies are contemplated to address the issue of
elevated end expiratory pressure.
[0018] In the prior art, utilization of the quasi-static
inspiratory pressure versus volume (P-V) curve has been advocated
as the basis for controlling a ventilator to carry out mechanical
ventilation.
SUMMARY OF THE INVENTION
[0019] The P-V curve represents the entire respiratory system and
may not adequately reflect the individual air spaces.
[0020] The invention further recognizes that recruitment continues
above the inflection point and may continue at airway pressures
beyond 30 cmH.sub.2O and that the primary mechanism of lung volume
change may be recruitment/de-recruitment (R/D) rather than
isotropic and anisotropic alveolar volume change. Lung volume
change to 80% of total lung capacity (TLC) may well be a result of
alveolar number increase (RID) rather than alveolar size.
Furthermore, recruitment is an end inspiratory phenomenon and may
be more closely related to plateau pressure rather than PEEP.
Therefore, to prevent tidal recruitment/de-recruitment (RID),
cyclic shear stress and low volume lung injury, the invention
contemplates that higher pressure may be required to achieve
complete recruitment. It is recognized that if PEEP levels are set
to end inspiratory pressure in order to completely recruit the
lung, the superimposition of tidal ventilation could result in
over-distension and high volume lung injury despite tidal volume
reduction.
[0021] Accordingly, the invention recognizes that recruitment is an
inflation phenomenon which continues beyond conventional PEEP
levels. Recruitment requires enough pressure to overcome
threshold-opening pressures and the superimposed pressure of the
airspace. Plateau pressure or continuous positive airway pressure
(CPAP) rather than PEEP level may be more appropriate determinants
of full lung recruitment. PEEP conceptually prevents de-recruitment
after a sustained inflation. Airway closure or de-recruitment is a
deflation phenomenon. Therefore, in accordance with the invention,
PEEP may be more suitable set to the inflection point of the
deflation limb of the P-V curve rather than that of the inflation
limb.
[0022] Greater hysteresis results from a downward and right
displacement of the inflation limb of the P-V curve.
[0023] Rather than PEEP, plateau or CPAP levels should be utilized
for bringing about airway opening (recruitment), allowing
substantially complete recruitment. In addition to adequate
threshold pressure, complete recruitment requires constant
inflation in order to sustain recruitment. Furthermore, sustained
recruitment facilitates ventilation on the deflation limb.
Ventilation occurs on the deflation limb of the P-V curve only
after a sustained recruitment maneuver. Sustained inflation pushes
the P-V curve to the outer envelope on to the deflation limb.
Stress relaxation accounts for a pressure reduction on the order of
20% within the initial 4 seconds of inflation.
[0024] In accordance with the invention, APRV mode ventilation is
established based on an initial set of ventilation parameters
selected as described in further detail below. Once ventilation has
been initiated, the parameter, T2, which defines the duration of
the ventilator release phase, is monitored and adjusted according
to at least one and preferable several alternative methods.
[0025] One method is to measure the expiratory gas flow rate during
expiration and to adjust T2, if necessary, such that T2 is
terminated when the rate of expiratory gas flow is at a value of
about 25% to 50% of its absolute peak value during expiration. To
achieve this, the ventilator is controlled to monitor the
expiratory gas flow rate and terminate the release phase when the
flow rate reaches a value within the aforementioned range.
[0026] Another method is to monitor expiratory flow and determine,
based on the flow pattern, whether the flow is of a restrictive or
obstructive nature, and adjust T2 accordingly. According to yet
another method, the expiratory flow is monitored for the presence
of an inflection point and T2 is adjusted as required to
substantially eliminate or at least reduce the inflection
point.
[0027] In the event of hypercarbia, the highest airway pressure
achieved during inspiration (P1) and the duration of the positive
pressure phase (T1) are both incrementally increased substantially
contemporaneously once or more as needed until blood carbon dioxide
declines to an acceptable level.
[0028] Accordingly to yet another aspect of the invention, weaning
from ventilation is carried out by initiating a series of
successive reductions in P1, each of which is accompanied by a
substantially contemporaneous, increase in the duration of
inspiration T1 such that over time, ventilation is transitioned
from APRV to a substantially CPAP mode.
[0029] Applicant's ventilation method and method for controlling a
ventilation apparatus based on same provides significant advantages
over the prior art. These advantages include an increase in vent
free days, lower ventilator-related drug costs, reduced ventilator
associated complications, reduced likelihood of high volume lung
injury, and reduced likelihood of low volume lung injury. These and
other objects and advantages of the invention will become more
apparent to a person of ordinary skill in the art in light of the
following detailed description and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a flowchart illustrating a preferred embodiment of
a ventilation method and control of a ventilator based on same
according to the invention;
[0031] FIG. 2 is a schematic airway pressure versus time tracing
for airway pressure release ventilation;
[0032] FIG. 3 is a airway pressure versus time tracing during the
inspiratory (P1) phase of ventilation;
[0033] FIG. 4 is an airway volume versus pressure curve
illustrating a shift from the inspiratory limb to the expiratory
limb thereof;
[0034] FIG. 5 is an inspiratory and expiratory gas flow versus time
tracing for airway pressure release ventilation;
[0035] FIG. 6 is an expiratory gas flow versus time tracing;
[0036] FIG. 7 is a set of expiratory gas flow versus time tracing
illustrating determination of whether flow pattern is normal,
restrictive or obstructive based on the shape of the tracing,
and
[0037] FIG. 8 is a set of airway pressure versus time tracings
illustrating ventilation weaning by successive reductions in
pressure PI and substantially contemporaneous increases in time
T1.
DETAILED DESCRIPTION
[0038] An operator interface coupled to the control unit typically
includes a graphical user interface as well as a keyboard and/or
pointing device to enable an operator to select the operating mode
of the ventilator and/or to enter or edit patient data and
operating parameters such as the pressures, times, flows, and/or
volumes associated with one or more ventilation cycles.
[0039] Referring to FIG. 1, the invention contemplates initiating
ventilation of a patient in an APRV mode based on initial
oxygenation and ventilation settings. The airway pressure during
expiration (P2) is substantially zero throughout ventilation to
allow for the rapid acceleration of expiratory gas flow rates.
Typically, the fraction of oxygen in the inspired gas (FiO.sub.2)
is initially set at about 0.5 to 1.0 (i.e. about 50% to 100%). The
highest airway pressure achieved during inspiration (PI) must be
sufficiently high to overcome airspace closing forces and initiate
recruitment of lung volume. PI may suitably be initialized at a
default value of about 35 cmH.sub.2O. Alternatively, PI may be
established based either on the severity and type of lung injury or
based on recruitment pressure requirements. The latter method is
preferred in cases where the ventilation/perfusion ratio is less
than or equal to about two hundred millimeters of mercury (200
mmHg). The ventilation perfusion ratio is preferably monitored
continuously. It is the ratio of the partial pressure of oxygen in
the blood of the patient to the fraction of oxygen present in the
inspired gas (i.e. PaO.sub.2/FiO.sub.2 but is commonly abbreviated
as P/F).
[0040] Where the type and severity of lung injury are characterized
by a P/F of greater than about 350 mmHg, an initial value of P1
within the range of about 20 cmH.sub.2O to 28 cmH.sub.2O is
preferably established. On the other hand, if the P/F ratio is less
than about 350 mmHg, P1 is preferably initialized within the range
of about 28 cmH.sub.2O to 35 cmH.sub.2O.
[0041] In situations where the P/F ration is less than or equal to
about 200 mm Hg, such as may occur where the patient's initial
injury is non-pulmonary and/or lung injury is of an indirect
nature, the invention contemplates establishment of P1 at a value
of between about 35 mmHg and 40 mmHg but preferably not appreciably
above 40 mmHg.
[0042] Initially, the duration of the positive pressure phase (Ti)
is established at a value within the range of about 5.0 to about
6.0 seconds unless the measured PaCO.sub.2 is greater than about 60
mmHg.
[0043] Once initial values of P1, P2, T1 and T2 have been
established, ventilation continues in a repetitive APRV mode cycle
generally as illustrated in FIG. 2. During management of
ventilation in accordance with the invention, the initial values of
one or more of these parameters are re-assessed and modified in
accordance with measured parameters as will now be described with
continued reference to FIG. 1.
[0044] In management of ventilation in accordance with the
invention, a principal goal is to maintain the level of carbon
dioxide in the blood of the ventilated patient (PaCo.sub.2) at a
level of less than or equal to about 50 mmHg. Toward that end,
arterial PaCO.sub.2 is monitored continuously or measured as
clinically indicated and the ventilator controlled to adjust
ventilation as follows. Any time after ventilation has commenced,
but preferably soon thereafter or promptly upon any indication of
hypercarbia (PaCO.sub.2 above about 50 mmHg), the setting of T2 is
optionally but preferably checked and re-adjusted if necessary.
According to the invention, optimal end expiratory lung volume is
maintained by titration of the duration of the expiration or
release phase by terminating T2 based on expiratory gas flow. To do
so, the flow rate of the expiratory gas is measured by the
ventilator and checked in relation to the time at which the
controller of the ventilator initiates termination of the release
phase. The expiratory exhaust valve should be actuated to terminate
the release phase T2, at a time when the flow rate of the
expiratory gas has decreased to about 25% to 50% of its absolute
peak expiratory flow rate (PEFR). An example is illustrated in FIG.
5. In that example, T2 (sometimes referred to as Tlow) terminates
by controlling the expiratory exhaust valve to terminate the
release phase when the expiratory gas flow rate diminishes to 40%
PEFR.
[0045] If monitoring of PaCO2 indicates hypocarbia is present (i.e.
PaCO.sub.2 less than about 50 mmHg), T1 is increased by about 0.5
seconds while maintaining PI substantially unchanged. Should the
patient remain hypocarbic as indicated by subsequent measure of
PaCO.sub.2, weaning in the manner to be described may be initiated
provided oxygenation is satisfactory and weaning is not otherwise
contraindicated based on criteria to be described further
below.
[0046] The hypercarbic patient though is not to be weaned. In the
event of hypercarbia, the invention contemplates assessment of the
expiratory flow pattern before making significant further
adjustments to ventilation parameters. This assessment can readily
be carried out by a software program stored within the control unit
of the ventilator which carries out automated analysis of the
expiration flow versus time tracing. As illustrated in FIG. 7,
normal expiratory flow is characterized by flow which declines
substantially monotonically from the onset of the release phase
through its termination and does not fall off prematurely or
abruptly. Restrictive flow in contrast declines rapidly from the
onset of the release phase to zero or a relatively small value.
Obstructive flow tends to be more extended in duration and is
characterized by an inflection point beyond which the rate of flow
falls off markedly from its initial rate. FIG. 6 illustrates
another example of an obstructive flow pattern. Based on analysis
of flow data provided by expiratory flow sensors, the control unit
of the ventilator is programmed to determine whether flow is
obstructive or restrictive based on the characteristics just
described. If it is determined that obstructive or restrictive flow
is present, the invention contemplates adjusting T2 before making
any other significant adjustments to ventilation parameters. This
can be done according to either of two alternative methods.
[0047] One method is to adjust T2 to a predetermined value
according to whether flow is either obstructive or restrictive but
allowing T2 to remain at its previous value if flow is normal. In
the case of restrictive flow, T2 should be adjusted to less than
about 0.7 seconds. On the other hand, obstructive flow calls for a
T2 of greater duration, preferably greater than about 0.7 seconds
with 1.0 to 1.2 being typical.
[0048] PaCO.sub.2 should then be reassessed and concomitant
increases of about 0.5 seconds in T1 and about 2 cmH.sub.2O in P1
repeated as indicated in FIG. 1 until the patient is no longer
hypercarbic.
[0049] Upon meeting the latter objective, weaning in the manner to
be described may be initiated provided the ventilation goal
described earlier (i.e. a PaCO.sub.2 of less than about 50 mmHg) is
met and weaning is not otherwise contraindicated.
[0050] If such action does not result in raising oxygenation and
saturation to at least the goals of about PaO.sub.2 of about 80
mmHg and SaO.sub.2 of about 95%, P1 is increased to a maximum of
about 45 cmH.sub.2O and Ti is progressively further increased by
about 0.5 seconds to 1.0 seconds.
[0051] Once those oxygenation and saturation goals are met,
ventilation is controlled to maintain those goals while
progressively decreasing FiO.sub.2 and P1 toward the levels at
which initiation of weaning can be considered. More particularly,
P1 is decreased by about 1 cmH.sub.2O per hour while FiO.sub.2 is
decreased by about 0.05 about every thirty (30) minutes while
maintaining an oxygen saturation of at least about 95%.
[0052] That is, when PaCO.sub.2 remains below about 50 mmHg and
SaO.sub.2 remains at least about 95% at a P1 of about 35 cmH.sub.2O
and FiO.sub.2, if previously higher, has been weaned to a level of
not greater than about 0.5
[0053] However, during the second stage, the reductions in P1 take
place in increments of about 4 cmH.sub.2O and the increases in T1
are each about 2.0 seconds.
[0054] Once the patient is tolerating CPAP at about 5 cmH.sub.2O
with FiO.sub.2 of not greater than about 0.5, the patient's ability
to maintain unassisted breathing is assessed, preferably for at
least about 2 hours or more.
[0055] a.) SPO.sub.2 of at least about 0.90 and/or PaO.sub.2 of at
least about 60 mmHg;
[0056] b.) tidal volume of not less than about 4 ml/kg of ideal
bodyweight;
[0057] c.) respiration rate not significantly above about 35
breaths per minute; and
[0058] d.) lack of respiratory distress, with such distress being
indicated by the presence of any two or more of the following:
[0059] i) Heart rate greater than 120% of the 0600-hour rate
(through less than about 5 minutes above such rate may be
considered acceptable) [0060] ii) marked use of accessory muscles
to assist breathing; [0061] iii) thoroco-abdominal paradox; [0062]
iv) diaphoresis and/or [0063] v) marked subjected dyspnea.
[0064] If there is an indication of respiratory distress, CPAP at
an airway pressure of about 10 cmH.sub.2O should be resumed and
monitoring and reassessment carried out as needed. However, if
criteria a) through d) above are all satisfied, the patient may be
transitioned to substantially unassisted breathing such as by
extubation with face mask, nasal prong oxygen or room air, T-tube
breathing, tracheotomy mask breathing or use of high flow CPAP at
about 5 cmH.sub.2O.
[0065] During all phases of ventilation including initiation,
management and weaning, the patent should be reassessed at least
about every two hours and more frequently if indicated. Blood gas
measurements (PaO.sub.2 and SaO.sub.2 and PCO.sub.2) on which
govern control of ventilation according to the invention should be
monitored not less frequently than every two hours though
substantially continuous monitoring of all parameters would be
considered ideal. Blood gas measurements (PaO.sub.2 and SaO.sub.2
and PaCO.sub.2) that govern control of ventilation according to the
invention should be monitored not less frequently than every two
hours though substantially continuous monitoring of all parameters
would be considered ideal.
[0066] Just prior to and during weaning at least one special
assessment should be conducted daily, preferably between 0600 and
1000 hours. If not possible to do so, a delay of not more than
about four hours could be tolerated. Weaning should not be
initiated or continued further unless:
[0067] a) at least about 12 hours have passed since initial
ventilation settings were established or first changed,
[0068] b) the patient is not receiving neuromuscular blocking
agents and is without neuromuscular blockade, and
[0069] c) Systolic arterial pressure is at least about 90 mmHg
without vasopressors (other than "renal" dose dopamine).
[0070] If these criteria are all met, a trial should be conducted
by ventilating the patent in CPAP mode at about 5 cmH.sub.2O and an
FiO.sub.2 of about 0.5 for about five (5) minutes. If the
respiration rate of the patient does not exceed about 35 breaths
per minute (bpm) during the five (5) minute period weaning as
described above may proceed. However, if during the five (5) minute
period the respiration rate exceeds about 35 bpm it should be
determined whether such tachypnea is associated with anxiety. If
so, administer appropriate treatment for the anxiety and repeat the
trial within about four (4) hours. If tachypnea does not appear to
be associated with anxiety, resume management of ventilation at the
parameter settings in effect prior to the trial and resume
management of ventilation as described above. Re-assess at least
daily until weaning as described above can be initiated.
* * * * *