U.S. patent number 3,910,256 [Application Number 05/490,603] was granted by the patent office on 1975-10-07 for automated blood analysis system.
This patent grant is currently assigned to Primary Childrens' Hospital. Invention is credited to Justin S. Clark, Lloyd George Veasy.
United States Patent |
3,910,256 |
Clark , et al. |
October 7, 1975 |
Automated blood analysis system
Abstract
A system for automatically withdrawing blood from a patient and
testing various parameters of the blood, such as oxygen saturation,
hemoglobin, gas content (PO.sub.2, PCO.sub.2) and pH, includes a
withdrawal unit which automatically withdraws a measured volume of
blood, and returns all of it to the patient except a small measured
quantity which is provided to an analysis unit that measures the
gas content and pH. The withdrawal unit includes provision for
continuously monitoring patients' blood pressure, irrigation from a
standard I.V. source between blood withdrawals, or a constant low
flush of saline, alternatively, as well as detection of any air in
the blood, which results in shutting down the system and activating
an air alarm. The withdrawal unit also has provision for
automatically withdrawing a small sample of blood, measuring oxygen
content, and returning all blood to the patient, all on a
programmed basis. The analysis unit includes two-point gas and pH
calibration and includes use of calibration fluid for washout. In
each complete use cycle, blood from the withdrawal unit is washed
into the analysis unit and blood in the analysis unit is moved and
washed out using saline, water and calibration fluids. The
withdrawal unit may be used alone to acquire blood samples, and the
analysis unit may be fed by more than one withdrawal unit or by
manually-acquired blood specimens.
Inventors: |
Clark; Justin S. (Salt Lake
City, UT), Veasy; Lloyd George (Salt Lake City, UT) |
Assignee: |
Primary Childrens' Hospital
(Salt Lake City, UT)
|
Family
ID: |
26982060 |
Appl.
No.: |
05/490,603 |
Filed: |
July 22, 1974 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
319561 |
Dec 29, 1972 |
3838682 |
|
|
|
Current U.S.
Class: |
600/325;
73/64.41; 604/28 |
Current CPC
Class: |
G01N
35/00594 (20130101); G01N 35/00693 (20130101) |
Current International
Class: |
G01N
33/483 (20060101); G01N 35/00 (20060101); A61B
005/00 (); A61M 005/00 () |
Field of
Search: |
;128/1,2G,2R,2L,214B,214E ;356/39-42 ;73/64.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Medbery; Aldrich F.
Attorney, Agent or Firm: Foster; Lynn G.
Government Interests
The invention described herein was made in the course of work under
a grant or award from the Department of Health, Education, and
Welfare.
Parent Case Text
This application is a division of our copending U.S. Pat.
application Ser. No. 319,561, filed Dec. 29, 1972 and now U.S. Pat.
No. 3,838,682.
Claims
Having thus described typical embodiments of our invention, that
which we claim as new and desire to secure by Letters Patent
is:
1. A method of timing of blood withdrawal and examination system
connected to a patient via a catheter, comprising the steps of:
filling the system with at least one biologically inert fluid;
calibrating the system;
withdrawing blood, upon command, from the patient through the
catheter into the system in fluid-to-fluid contact with the inert
fluid;
sensing the inert fluid/blood interface at a blood examination
site;
automatically and instantaneously discontinuing the withdrawal step
when the sensing step occurs;
applying pressure to the inert fluid to push substantially all of
the blood out of the system through the catheter and back into the
patient.
2. The method of claim 1 wherein the withdrawing and applying steps
comprise the step of confining the flow of inert fluid and blood to
laminar flow in passageways of uniform cross-sectional area and
configuration.
3. The method of claim 1 further comprising the step of terminating
the withdrawing step if the sensing step does not occur within a
predetermined time.
4. The method of claim 1 further comprising the step of examining
at least one blood characteristic at the blood examination site and
providing a visual display of the results.
5. The method of claim 4 further comprising the step of initiating
additional automated blood withdrawal and examination at other
sites when said visually displayed results are abnormal.
6. A method of minimizing blood loss during blood withdrawal and
blood testing, comprising the steps of:
withdrawing blood, upon command, from a patient through a catheter
into a blood withdrawal system;
discharging only a predetermined quantity of blood from the
withdrawal system into a blood testing system while maintaining a
physical separation between the two systems;
creating a fluid/blood interface in the blood testing system;
displacing in unison fluid, blood and the interface into the blood
testing system;
sensing the fluid/blood interface at a blood testing site;
automatically discontinuing the displacing step when the sensing
step occurs;
testing the blood at said site;
applying pressure to the blood to discharge blood from the blood
testing system to waste.
7. The method of claim 6 further comprising the step of terminating
the displacing step if the sensing step does not occur within a
predetermined time.
8. The method of claim 6 further comprising the step of returning
substantially all of the blood in the withdrawal system to the
patient through the catheter.
9. A method of calibrating a blood monitoring system comprising the
steps of:
providing at least one source of calibration fluid;
displacing calibration fluid from the source through lines of the
system to at least one blood monitoring site;
causing a calibration measurement in respect to the calibration
fluid to be made at said site;
removing a quantity of blood from the patient through a
catheter;
creating an interface between the blood and the calibration
fluid;
simultaneously displacing the calibration fluid and the blood
within lines of the system so as to distinctly maintain the
interface while evacuating fluid from and introducing blood at said
site;
causing a blood measurement to be made at said site.
10. The method of claim 9 wherein the removing step precedes the
displacing step.
11. The method of claim 9 further comprising the step of flushing
blood from the lines of the system following the last-mentioned
causing step.
12. The method of claim 9 further comprising the steps of allowing
the calibration fluid and the blood respectively to equilibrate at
said site before causing said measurements to be made.
13. A method of calibrating a blood monitoring system comprising
the steps of:
placing one calibration fluid within lines of the system at one
monitoring site and another calibration fluid within lines of the
system at a second monitoring site;
causing a calibration measurement to be made at each site in
respect to the calibration fluid there disposed;
removing blood from the patient through a catheter into lines of
the system;
evacuating calibration fluid from the sites and replacing the
calibration fluid with blood;
causing a blood measurement to be made at each said site.
14. The method of claim 13 wherein each causing step comprises two
separate measurements each made at a different time.
15. The method of claim 13 wherein said evacuating step comprises
removing the two calibration fluids from said sites at different
points in time.
16. The method of claim 13 wherein said placing step comprises
separate acts each made at a different time.
17. The method of claim 13 wherein said placing, causing and
evacuating steps, respectively, occur at essentially the same point
in time.
Description
BACKGROUND
1. Field of Invention
This invention relates to automated blood analysis systems, and
more particularly to apparatus for automatically withdrawing and
testing blood.
2. Prior Art
The proper management of patients who are critically ill with
respiratory or cardiovascular disorders requires frequent
monitoring of various blood parameters such as oxygen saturation,
gas content and pH. While adequate oxygenation is necessary for
maintenance of life, it is also important to avoid excessively high
arterial PO.sub.2, particularly in new born infants, in order to
prevent Retrolental Fibroplasia and possible central nervous system
damage. Similarly, the duration of high oxygen concentrations must
be kept to a minimum in infants to prevent possible toxic effects
in the lungs. There are numerous other situations, such as in
diagnosis of critical illness, monitoring a patient's condition
during certain corrective procedures, and in intensive care
programs wherein blood paramaters must be frequently analyzed.
However, frequent manual withdrawal of blood is undesirable due to
the increased opportunity for the entrance of air emboli in the
blood stream, and to the attendant necessary morbidity,
particularly in new born infants. Similarly, multiple usage of an
indwelling catheter has heretofore nonetheless required
rearrangement of external tubing to adjust between blood withdrawal
and irrigation configurations, which is subject to human error and
which also presents increased incidence of air emboli infusion.
Some systems known to the prior art require a constant flow of
blood therethrough which unnecessarily increases blood contact with
foreign surfaces, which can increase the opportunity for
contamination of the blood, or which may damage the blood. On the
other hand, systems known to the art which discharge withdrawn
blood to waste after testing thereof have utilized an excessive
amount of blood which becomes particularly intolerable in the case
of critically ill new born and pre-mature infants. Other systems
subject the patient to a risk of electric shock due to a continuous
contact existing between the patient and electric potentials within
the blood testing equipment or sensors. Systems which return blood
to the patient cannot be used for destructive tests (such as
glucose analysis, flame photometry, etc.).
As is known, it is common to employ saline as a compatible vehicle
for use in blood pumps and tubing systems of blood test units since
some of its chemical properties approach that of blood. However,
depending upon the characteristics of the individual patient, blood
equipment and use, it is possible to infuse undue amounts of saline
into the patient's blood stream, thereby resulting in a dangerous
sodium buildup. Use of intravenous solutions (I.V.) which are
desirable to the patient for its nutritive or other value, as a
vehicle in blood systems avoids the sodium buildup problem, but, on
the other hand, has a tendency to contaminate the system with
respect to the blood test transducers which are used.
Some blood parameters differ markedly from saline and pure water,
which are used for cleaning a system, and may concurrently require
a test principle which includes a very slow process, such as
diffusion across a membrane. Repetitive usage of an effective blood
analysis system requires automated washout between samples. On the
other hand, efficient usage of such a system, particularly with
multiple blood sources, dictates that a rather rapid analysis cycle
be achievable. Blood analysis units known to the art require both
manual cleaning and manual calibrations between samples.
In addition, systems known to the art do not provide adequate tests
for membrane leakage in gas detection tests.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
A principal object of the present invention is to provide improved
blood analysis capability.
Another object of the invention is to provide improved automatic
blood withdrawal and analysis units.
A further object of the invention is provision of a blood
withdrawal unit capable of automatic interspersion of blood
withdrawal cycles with constant irrigation or flush cycles for use
with a continuously indwelling catheter.
Still other objects of the invention include provision of blood
apparatus with improved self cleaning, automatic calibration,
shorter equilibration times, and with improved integrity of the
test results.
Further objects of the invention include an automated blood
analysis system which requires very little blood, isolates
hazardous blood testing units from the patient, is self-calibrating
and self cleaning, and is capable of utilization with multiple
automatically or manually derived blood specimens.
Other important objects are the provision of an automatic blood
testing system having: a novel fluid reservoir; capability to
return substantially all withdrawn blood to the patient; an
analyzer which can be shifted between and used with any one of
several blood withdrawal units; an analyzer/withdrawal arrangement
where only the withdrawal unit requires sterilization and
contamination of the withdrawal unit by the analyzer is precluded;
a combination blood withdrawal/infusion unit where intravascular
(I.V.) solution flow is continuous, i.e. to the patient during the
infusion mode and to waste during blood withdrawal; initial
calibration fluids which are used to displace blood within the
blood testing system; a control arrangement based on sensing a
blood/transparent fluid interface which moves within the system
according to a program.
According to the present invention, an automated blood system
adapted for connection with an indwelling catheter includes
alternatively operable means for providing I.V. infusion, constant
catheter flush, or blood withdrawal, without necessitating
rearrangement of apparatus, by means of a novel and improved
automated valving arrangement.
In accordance with the present invention, automatic blood analysis
apparatus is provided with a plurality of sources of fluid, said
fluid having a characteristic similar to a characteristic of blood
which is to be tested, said apparatus including testing stations
interconnected with said fluid sources by valve means programmed in
a fashion to provide calibration of said test station prior to the
testing of blood therewith and further calibration following the
testing of blood therewith. In further accord with the present
invention, automated blood testing apparatus includes a gas test
station and a pH test station, and valving means for applying blood
first to said pH test station and then to both said pH test station
and said gas test station, the fluid in said test stations being in
electrical communication with one another, said apparatus providing
a first test of blood at said pH test station at said first time
and a second test at said pH station at said second time, a
substantial variation in the results of said first and second tests
being indicative of a fault at said gas test station. In still
further accord with the present invention, washout water used to
cleanse a test station is provided with a measure of a substance
for which blood is to be tested, thereby to provide the presence of
said substance in an amount on the same order of magnitude of the
concentration of said substance normally found in a test therefor,
whereby to reduce the equilibration time required to perform a test
for said substance. In accordance still further with the present
invention, improved programming and arrangement of valve means
enhances the drawing of blood into test stations, and the cyclic
cleaning of a plurality of test stations with various fluids.
The present invention provides automatic blood withdrawal and/or
automatic blood testing with great safety and at a relatively high
rate of speed. Blood/Transparent fluid interface is minimized by a
novel reservoir and the interface serves to control the operation
of the system. Blood withdrawal apparatus in accordance herewith is
capable of withdrawing precise amounts of blood, for use in the
automated analysis operations or otherwise, in between the
regulated infusion of catheter flushing solution or intravenous
irrigation solution. The invention permits rapid cyclic testing of
different blood specimens, with automatic washout between tests,
and automatic and efficient calibration. The invention eliminates
the need for multiple catheters or reconfigurations of withdrawal
systems in order to achieve steady state monitoring and infusion in
conjunction with periodic blood withdrawal. Blood withdrawal may be
achieved utilizing solutions which are compatible with blood
testing, or utilizing intravenous irrigation solutions which avoid
a buildup of excessive concentrations of undesirable compounds in
the blood. The automated testing of blood is achieved in accordance
with the invention in a manner utilizing extremely small amounts of
blood and returning substantially all withdrawn blood to the
patient. Minute amounts of blood used for certain tests are
exhausted to waste, thereby avoiding any risk of cross
contamination and blood damage problems. Testing of blood from a
plurality of automatic or manually withdrawn specimens in a
relatively short period of time is readily achieved, due not only
to the complete autonomy of the automated withdrawal and testing
units, but as well to fast and efficient washout and calibration
procedures. One analysis unit can service several withdrawal units.
Need for sterilization of the analyzer is obviated and cross
contamination, analyzer-to-withdrawal unit, is avoided. The
withdrawal unit may be constructed to both infuse I.V. fluid and
withdrawal blood, with I.V. fluid being exhausted to waste during
the withdrawal mode. Preferably, calibration fluids drive the blood
within the system.
Other objects, features and advantages of the present invention
will become more apparent in light of the following detailed
description of a preferred embodiment thereof, as illustrated in
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified block diagram of a system in which the
present invention may be incorporated;
FIG. 2 is a schematic block diagram of an automated blood
withdrawal unit in accordance with the present invention;
FIG. 3 is a schematic block diagram of an automated blood analysis
unit in accordance with the present invention;
FIG. 4 is a simplified schematic block diagram of a timing unit
which may be used in conjunction with the embodiment of the
invention illustrated in FIGS. 2 and 3;
FIG. 5 is a diagram illustrating a mode of cyclically timing the
apparatus of the embodiments of FIGS. 2 and 3; and
FIG. 6 is a perspective representation of a preferred fluid
reservoir.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring now to FIG. 1, a blood analysis system 20 which may
incorporate the precepts of the present invention includes one or
more withdrawal units 22, an analysis unit 24 and a timing unit 26,
which may be included within a calculation unit 28 (not shown) if
desired, or may be provided separately as shown herein. Even though
more than one withdrawal unit may be used, on a consecutive basis,
to deliver blood to the analysis unit, physical isolation, as
explained more thoroughly hereinafter, avoids cross contamination.
The calculation unit 28 may include indicators 30 if desired, or
these may be provided separately, such as at an intensive care unit
nurses' station or other remote location. The calculation unit 28
may, if desired, comprise a blood analysis calculation unit of any
type heretofore known in the art, there being a plethora of such
units available in the marketplace for "bench" testing of blood
samples. On the other hand, the calculation unit 28 may comprise a
computing system, such as a large scale computer which may be time
shared with other functions, or a minicomputer dedicated to
operation with a withdrawal unit 22 and an analysis unit 24 of the
type disclosed herein. In the event that the calculation unit
includes a multi-function computer of some sort, the timing
functions may be readily provided thereby, rather than by a
discrete timing unit 26 of the type described with respect to FIG.
4 hereinafter. It should be understood that the apparatus which
provides the timing and calculation of test results is not germane
to the present invention; instead, the preset invention is
concerned with the improvements in the withdrawal unit 22 as
described with respect to FIG. 2 hereinafter and in the analysis
unit 24 as described with respect to FIG. 3 hereinafter, and with
the timing of functions performed thereby so as to achieve new and
improved operational functions and results.
Referring now to FIG. 2, a fitting 32, which may be of the well
known Luer type of fitting, is adapted for connection with a
suitable arterial, vensus, or umbilical catheter 33 of any type
known for use in fluid communication with the blood system of the
patient. The fitting 32 is connected by tubing 34 to an oximeter 36
which is provided with electrical inlet connections 38 and
electrical output connections 40. The tubing 34 must be essentially
impervious to diffusion of gas to prevent or minimize O.sub.2 and
CO.sub.2 losses. KEL-F and nylon tubing have proved satisfactory.
The oximeter 36 may be of any well known type which typically
measures oxygen saturation. The oximeter 36 is calibrated with
saline in the tubes of the withdrawal unit which remains there and
is used as the medium for displacing blood within the withdrawal
unit. The appearance of a stable blood/saline interface at the
oximeter terminates withdrawal thereby minimizing the amount of
blood removed. The blood is returned to the patient, as hereinafter
more fully explained. This procedure allows more frequent
examination of blood. If a stable blood/saline interface does not
appear at the oximeter during withdrawal after a predetermined
time, withdrawal ceases as constant volume pump 140 only cycles
once.
The oximeter 36 is connected by tubing 42 to a fitting 44 and by
means of additional tubing 46 to a pair of air detectors (AD) 48,
50. The air detectors 48, 50 include an electric signal input 52
and respective signal outputs 54, 56. It is to be noted that the
air detector output terminals 54, 56 are depicted in a circular
configuration in contrast with the square configuration of the
oximeter output terminals 40. This is to distinguish between
electrical signals which are used directly in the control of the
system of the present invention (such as signals at the terminals
54, 56) which are depicted in round configuration, from output
signals which are used externally of the system so as to derive
information relating to blood which is being tested (such as
signals at the terminals 40) which are depicted in the square
configuration. The air detector 50 is connected by tubing 58 to a
port 60 of a fluid valve 62 which, along with similar other valves
herein, is depicted schematically as a block having a pair of solid
lines illustrating fluid paths 64, 66 which are normally connected
or conductive to fluid when the valve is in its normal or
deenerized state, along with dashed lines depicting flow paths 70,
72 which are normally not connected and not conductive to fluid
when the valve is in its normal, deactivated, or deenergized state.
Thus, the port 60 is connected by the path 64 to a port 74 and a
port 76 is connected by path 66 to a port 78 when the valve is
deenergized as shown in FIG. 2. On the other hand, ports 60, 78 are
interconnected by the path 70 and ports 74, 76 are connected by the
path 72 when the valve is activated or energized in response to an
electric signal applied at a terminal 80a. It should be noted that
the ports 60, 74, 76, 78 may act either as inlets or outlets
without regard to whether the valve is in its operated or
unoperated state. The valve 62, along with other similar valves
herein, is designed to be resiliently urged into the inactivated
state by a suitable means such as a spring so that all flow will
stop in the event of a power failure, or in the event of detecting
air in the blood by the air detectors 48, 50 (in a manner to be
described hereinafter). The valve 62 (and other similar valves) may
be a pneumatically actuated valve, the pneumatic actuation in turn
being in response to an electrically operated solenoid valve.
Valves of this type are made by several manufacturers and are
available in the marketplace.
The port 74 is connected by tubing 82 to an I.V. source and pump
apparatus 84 which may be of any conventional type used for
irrigation and/or infusion purposes. With the valve 62 deenergized
as shown in FIG. 2, the I.V. source and pump 84 is connected
through the valve 62, the air detector 50, the connector 44 and the
oximeter 36 to the connector 32 for fluid communication with a
catheter. When valve 62 is energized, blood is withdrawn from the
patient and I.V. solution from 84 is exhausted to waste through
port 76 and conduit 112. In this way no damage to the system
results which would otherwise threaten because of pressure forces.
The I.V. source and pump 84 may be used to infuse intravenous
solution into the patient through the catheter at 32.
The air detector 48 is connected by tubing 86 to a port 88 of a
valve 90, another port 92 of which is connected by tubing 94 to the
port 78. A port 96 is connected by tubing 98 to a pressure
transducer 100, a single path valve 102, and a flow restrictor 104.
The valve 102 may be actuated at 103 to conduct fluid by manual
application, so as to use the saline source 110 with a high flow
rate for flushing out various lines. However, this forms no part of
the invention herein, except to illustrate the versatility thereof.
The pressure transducer 100 can be of any type well known for the
purpose of deriving the patient's blood pressure, and provides an
electrical signal indicative thereof at an output terminal 106.
This signal may be utilized in any well known fashion, and the
transducer forms no part of the present invention. The valve 102
and flow constrictor 104 are connected by tubing 108 to an 8 psi
saline solution source 110. With the valve 102 closed as shown, the
flow constrictor 104 will provide a very minute, constant,
low-pressure flow of saline to the tubing 98 which may be used as a
constant flush system to prevent clotting at the end of the
catheter connected to the connector 32 during prolonged use,
between withdrawal cycles. It should be noted that this function of
the apparatus is unnecessary when irrigation is being regularly
provided from the I.V. source 84, as described hereinbefore.
Therefore, the saline from the source 110 is normally passed by
valves 90, 62 through the port 76 and a suitable means 112 to
waste. The means 112 may comprise tubing leading to a waste bucket,
or it may simply comprise a syrine attached directly to the port
76.
The valve 90 includes a port 114 connected by tubing 116 to a port
118 of a valve 120, which includes a port 122 connecting with a
means 124 leading to a blood cup which is described hereinafter
with respect to FIG. 3. The means 124 may otherwise comprise tubing
leading to any receptacle for blood, or a syringe to receive blood
which may be attached directly to the port 122. The valve 120 also
includes a port 126 leading to tubing 128 which is provided in
sufficient length (such as by inclusion of loops 130 therein) to
serve as a reservoir on the order of two milliliters in capacity.
The other end of the tubing 128 is connected to a port 132 of a
valve 134 which includes aa port 136 connected by tubing 138 to a
constant volume pump 140. The exact nature of the constant volume
pump is immaterial to the present invention with the exception of
the fact that if the pump 140 provides a constant known volume of
fluid per unit of time that it is actually actuated, the volume
displacement for a complete stroke also will be constant. However,
the pump 140 may comprise a syringe driven by a piston within a
cylinder, the piston in turn being driven by air supplied thereto
over tubes 142, 144 under control of a valve 146 which is connected
by a tube 148 to a source 150 of air at 30 psi (for instance). The
valve in turn is responsive to an OR circuit 152 so that it will be
actuated in response to signals applied on a terminal 154 or on a
terminal 156. With the valve 146 deactivated as shown, air is
applied over the tube 144 to cause a cycle which pushes blood from
the pump 140; when the OR circuit 152 is energized by a signal on
either of the terminals 154, 156, it activates the valve 146 to
apply air pressure from the source 150 to the tube 142 and cause a
cycle which draws fluid into the pump 140. The valve 120 may be
activated by a signal from an OR circuit 158 in response to
electric signals at either of two terminals 160, 80c. Provision of
the OR circuits 152, 158 permits operation of the pump 140 and the
valve 120 in response to diverse controls; similarly, the valve 134
is actuated in response to an electric signal from an OR circuit
162 which in turn may operate in response to electrical signals
applied on either of two terminals 164, 80d, in a manner which is
described in detail hereinafter with respect to FIGS. 4 and 5.
Briefly, by actuating the valves 62, 90, 120 and 134 by the
simultaneous application of electric signals to terminals 80a, 80b,
80c, and 80d, the air detector 50 (and therefore a catheter
connected to the connector 32) will be connected to the pump 140,
and the I.V. source 84 will be vented through the path 72 to waste.
This enables making a short stroke with the pump 140 so as to draw
blood into the oximeter 36 for the purpose of monitoring blood
oxygen saturation, which can be done frequently with substantially
no blood loss or interruption of any other functions; such a test
is extremely useful, when performed on a frequent, cyclic basis, to
provide an indication of when a more complete blood analysis may be
required.
The valve 134 includes a port 166 connected by tubing 168 to a
saline reservoir 170; this is used, as is described more fully
hereinafter with respect to FIGS. 4 and 5, to aid in the withdrawal
of blood from (and return of a portion of the blood to) the
patient, the insertion of some of the blood in the blood cup for
analysis, and in washing out the system. Preferably, the reservoir
170 takes the form shown in FIG. 6, i.e. a constant diameter small
bore tubing 170' coiled about a suitable retainer such as the
cylindrical retainer 171. The tubing 170' presents a female port
173, through which additional saline may be introduced to replenish
the supply. This configuration has been found to solve the
heretofore substantial problem of blood/fluid interface mixing. By
restricting the blood/saline interface, infused saline is
minimized.
The valve 134 also has a port 172 which is shown connected to a
connector 174 having a plug 176 therein. The port 172 may
advantageously be used with a manual flush syringe, if desired.
The valve 120 is provided with an additional port 178 which is
connected to connector 180 blocked off by a plug 182. The connector
180 may be used to facilitate connection to the valve 120 of
pressure transducer apparatus and saline flush apparatus similar to
the apparatus 98-110 described hereinbefore. With such an
arrangement, constant flush may be provided through the valves 90,
120, when deenergized as shown, and through the air detector 48 to
the catheter connected to the connector 32. Then, if desired, a
second catheter may be connected to the connector 44 (disconnecting
the tube 46 from the tubing 42) so as to allow the running of two
systems simultaneously, the catheter connected to the connector 44
being operable either in conjunction with a constant saline flush
or in conjunction with an I.V. irrigation, as described
hereinbefore, in dependence upon the setting of the valve 62. This
illustrates the versatility of the present invention.
It is sometimes desirable to fit the influent end of the withdrawal
unit with an alarm, so that when blood unexpectedly appears, the
attendant is promptly notified. Such an alarm would be shut off
during intentional withdrawal of blood.
Referring now to FIG. 3, an embodiment of an analysis unit 24 in
accordance with the present invention includes a blood cup 190
which may receive blood manually from a syringe, or by being
properly disposed may receive blood by other means 124 (FIG. 2)
from one withdrawal unit. The blood cup 190 represents a distinct
interface between the withdrawal unit and the analysis unit
permitting blood to reach the analyzer by force of gravity but
preventing analyzer fluids from reaching the patient by maintaining
a distinct physical separation between the units. Thus, the
analyzer fluids (calibration gases and liquids) and the components
of the analyzer need not be sterile. As a result all constraints
required by a sterile analyzer are removed and the analyzer may be
used on one patient after another without appreciable time
delay.
In addition, the blood cup 190 may receive a water washout solution
over tubing 192, and either of two buffer solutions over tubing
193, 194. The tubing 192-194 is connected to respective check
valves 196-198 which are in turn connected by respective tubing
200-202 to additional check valves 204-206 and to corresponding
syringe pumps 208-210. The pumps 208-210 provide a push stroke in
response to electric signals applied to corresponding terminals
212-214. The volumetric capacity of the pumps is such that upon
release of the signals on terminals 212-214 the pumps provide draw
cycles through the check valves 204-206 to supply the desired
amount of fluid to be driven through the check valves 196-198 upon
the next energization of the pumps by the application of electric
signals at the terminals 212-214. The check valves 204-206 are
connected to a source 216 of water and to sources 218, 220 of two
different buffer solutions. The buffer one solution in the source
218 may comprise a dilute solution of Na.sub.2 HPO.sub.4 and
KH.sub.2 PO.sub.4 having a pH of about 7.45, and the buffer two
solution in the source 220 may be a dilute solution of Na.sub.2
HPO.sub.4 and KH.sub.2 PO.sub.4 having a pH of about 6.88. The two
different pHs allow for two calibration points on a pH test as
described hereinafter.
The blood cup 190 is connected by tubing 222 to a port 224 of a
valve 226 which alternatively connects the blood cup 190 to tubing
228 of a pH tester 230 and through tubing 232 connected to a blood
gas tester 234. An important feature of the present invention,
which is described more fully with respect to FIGS. 4 and 5
hereinafter, is the utilization of the pH tester 230 to check the
blood gas tester 234 for leaks. In order to achieve this, a means
236 is provided to insure that the liquid in the tubing 228 and in
the tubing 232 are at the same electrical potential. The means 236
illustrated in FIG. 3 may comprise a stainless steel wire which
passes through the walls of the respective tubing 228, 232 so as to
provide for an electrical conduction therebetween. On the other
hand, depending on the nature of the valve 226, it is possible that
in some utilizations of the present invention the electrical
conductivity can be maintained by means of wetness of the surfaces
within the valve 226, without regard to whether the valve is
actuated or not. The tube 228 provides fluid connection to a pH
electrode 238 which may be of any conventional known type that
provides an electric signal at an output 240 which, in conjunction
with a reference electrode signal at an output terminal 242
provides a measure of the pH of the fluid, therein. The electric
output terminal 242 is connected to a reference electrode 244 of
the type known in the art, which may be connected by tubing 246, or
in any other suitable fashion, to the primary electrode 238. The
reference electrode 244 is connected by tubing 248 to a block
detector 250 which may be of any conventional type, such as a
photodetector system which senses the opacity of the fluid therein,
thereby recognizing the difference between blood and either gas or
saline solution. The blood detector 250 is provided with an
electric current applied over an input terminal 252 to operate a
light source therein, and the photo-detector therein provides an
electric signal at an output terminal 254 which is a measure of the
transmissivity of the fluid flowing therein. Since this is of
conventional nature and forms no part of the present invention,
further description is not given herein. The sensing of the
blood/fluid interface at blood detector 250 and/or blood detector
268' controls the positioning of blood which is pulled from the cup
and accordingly, the needed volume of blood. If blood is not sensed
within a predetermined time, an error is indicated, measurement is
terminated and the system is flushed. In this way the amount of
blood used by the analyzer and not returned to the patient is
minimal. The blood detector is connected by tubing 256 to a port
258 of a valve 260 which is always operated in conjunction with the
valve 226 by simultaneous application of electric operating signals
to a pair of input terminals 262a, 262b, as is described more fully
hereinafter.
The tubing 232 is connected to gas electrodes 264 which provide
electric signals at a pair of output terminals 267, 268. The gas
electrodes may be conventional membrane-type electrodes for
measuring PO.sub.2 and PCO.sub.2, and form no part of the present
invention. The gas electrodes 264 are connected by tubing 266 to a
blood detector 268' which is similar to the blood detector 250
including an electric input terminal 270 and an electric output
terminal 272. The blood detector 268' is connected by tubing 274 to
another port 276 of the valve 260. When deenergized, the valve 226
provides flow of blood from the blood cup 190 into the blood gas
detector 264 and through the port 278 to port 279 of a pump valve
280. When energized, the valve 226 connects the blood cup 190 to
the pH tester 230 and connects the gas detector 234 through a port
282 to tubing 284 or other suitable waste disposition means. When
the valve 226 is energized, the valve 260 is also energized,
connecting the pH tester 230 through the port 258 of valve 260 to
port 279 of the pump valve 280, but also connecting the gas tester
234 through ports 276 and 286 of valve 260 to a port 288 of a
calibration gas valve 290 by a tubing 291. The pump valve 280
includes a port 292 connected to a constant volume pump 294 and a
port 296 connected by a suitable tubing 298 or other means to a
proper disposition for liquid waste.
The port 288 of the valve 290 is normally connected through a port
302 and tubing 304 to a flow constrictor 306 which in turn is
connected by tubing 308, a valve 309 (operated by a signal at a
terminal 310), and tubing 311 to a source 312 of a high PO.sub.2
and PCO.sub.2. The tubing 308 also applies such to a variable flow
constrictor 313 which is provided with a manual adjustment 314 to
adjust the amount of flow therethrough. This provides gases from
the source 310 to the water source 216 over tubing 316, thereby to
provide sufficient carbonate in the water of the source 216 so that
the gas electrodes 264 will, after being washed with water from the
source 216, have a substantial carbon dioxide concentration
diffused through the membranes prior to a final calibration of the
unit. That is, in the process of using calibration gas to drive
washout water through the unit, the concentrations will not be so
depleted in the gas electrodes 264 so as to require an undue
equilibration time for a final test after all blood is washed
therefrom.
The valve 290, when activated by an electric signal at an input
terminal 320, connects its port 288 with a port 322 and tubing 324
to another flow restrictor 326 which is connected by tubing 328 to
a source 330 of low PO.sub.2 and PCO.sub.2. Since the sources 312,
330 are under pressure, they are used, as described hereinafter, in
the process of cleaning out the gas electrodes 264. The analyzer is
calibrated before blood is introduced. Specifically, a liquid
calibration fluid is used to calibrate pH electrode 238 and a gas
calibration fluid is used to calibrate gas electrodes 264.
Thereafter, the calibration fluids are retained in the analyzer and
used, responsive to negative pressure, to displace blood within the
analyzer after it is received at cup 190. In this way the
calibration is preserved.
Referring now to FIG. 4, the timing unit 26 includes some source of
ordinary power 340 which is assumed to include means 342 for
turning it on and off. Such power may simply comprise 60 cycle 120
volt power. The source 340 is connected by a line 344 to a 1/6
revolution per minute motor 346 through a normally open switch 348
and a line 350. The switch 348 is normally open and must be
activated by a signal on a line 352 from an OR circuit 354 in order
to apply power from the line 344 to the motor 346. The motor is
connected by shafts 356, 357 to a one track rotary timer 358 and a
sixteen track rotary timer 359. The timers 358, 359 are supplied
power from a valve power source 360 over a line 361. When it is
desired to run the withdrawal unit for periodic oximeter testing
only, an oximeter ON switch 364 may be closed applying power from
the line 361 to a set input of a latch 365 which provides a signal
on a line 366 to operate the OR circuit 354 and apply power to the
motor 346. At the same time, the sinal on the line 366 applies
power to the terminal 80 which in turn is applied in FIG. 2 to all
of the terminals 80a-80d. This connects the constant volume pump
140 (FIG. 2) through the valves 62, 90, 120 and 134 to draw blood
through the air detector 50 and the oximeter 36 for the purpose of
testing the oxygen saturation of the blood. Within the one track
timer 358, a single contact element per revolution is provided, so
as to provide a signal on a line 368 to the terminal 154 which will
cause the OR circuit 152 (FIG. 2) to operate the valve 146 and
initiate a short stroke of the pump 140. For instance, the length
of the signal on the line 368 (and therefore the length of time
duration of the pump stroke) may be approximately 8 seconds so as
to draw approximately 0.5 of a milliliter of blood through the
oximeter 36, and then restore it back to the patient. This is
readily achieved by providing a contact in the timer 358 which
extends over 8.degree. (the same number of degrees as is desired
seconds since the 1/6 rpm motor 346 will cause the timer to
complete one revolution in 360 seconds - 6 minutes). Because of its
simplicity, the internal structure of the timer 358 has not been
shown. Once the switch 364 is closed, the testing of the blood in
the oximeter will continue cyclically until it is desired to cease,
while is achieved by depressing an oximeter OFF switch 370. This
causes an OR circuit 372 to reset the latch 365 so as to remove
power from the line 368, thereby deenergizing the terminal 80 to
return the valves in FIG. 2 to their unenergized state, and causing
the switch 348 to resume its normally open condition so that no
more power is applied to the motor 346.
Additionally, the OR circuit 354 may be operated by a signal on a
line 374 in response to the setting of a bistable device such as a
trigger or latch 376 whenever full automatic withdrawal and
analysis cycles are being performed under the control of the
sixteen track rotary timer 359. The sixteen track timer 359 has
sixteen tracks of contacts which are arranged as shown in FIG. 5.
If the timer 359 is a drum timer, then FIG. 5 depicts the contact
arrangement simply by joining the left end thereof (zero seconds in
time and zero arcuate degrees) with the right end thereof (360
seconds in time and 360 arcuate degrees). On the other hand, if the
sixteen track timer 359 is arranged in the form of a disc, then it
may be profitable to provide on the radially inward tracks those
contacts which are very small and do not consume much space whereas
the larger contacts, or ones that have to be extremely accurate,
may be placed on the radially outward tracks, all as is well known
in the rotary shaft encoder art. Power to the contacts within the
timer 359 is supplied by the line 361. Starting a full withdrawal
and analysis cycle is achieved by setting the latch 376 by means of
depressing a START button 380, which will cause the latch 376 to
remain energized until the end of the complete cycle, which occurs
at about 355 seconds after initializing by the generation on a
motor control line 381 of a signal which indicates that the cycle
is complete. This is applied to an OR circuit 382 which causes
resetting of the latch 376. The OR circuit 382 will also be
operated by an OR circuit 384 in response to signals at either of a
pair of terminals 54, 56 (FIG. 2) indicating that air bubbles have
been detected in the blood lines. The OR circuit 384 may also
operate an alarm 396 so as to advise an attendant at an intensive
care nurses' station or otherwise that air has been detected in the
lines. While the rotary timer 359 is operating, it presents signals
on a plurality of lines to operate valves and pumps so as to cause
direct cyclic operation of both the withdrawal unit and the
analysis unit for a complete automatic withdrawal and sampling of
blood, together with washout and calibration thereof. Each of the
lines at the output of the rotary timer, depicted as being within a
trunk of fifteen lines 398, is provided with an appropriate legend,
and is connected to the electric terminal which it operates in
FIGS. 1, 2 or 3.
Specifically, the signal lines 398 from the sixteen track timer 359
include a signal causing a test of the air detectors on a line 399,
which operates a normally-open switch 400 to short-circuit a
resistor 402, so as to provide more current from an LED power
source 404 through the terminal 52 to the air detectors 48, 50
(FIG. 2). This over-powers the air-detectors and forces an alarm
condition even though there is liquid in them, unless they are
inoperative.
The air detector and its operation form no part of the present
invention; however, it should be obvious that combination of the
signal on the line 52 and a lack of signals on the line 54, 56
could operate an OR circuit similar to the OR circuit 384 to create
an alarm condition which could turn off the latches 365 and 376 and
operate the alarm 396 if the air detectors are not working. A
withdrawal pump signal which causes the withdrawal pump 140 (FIG.
2) to initiate a pull stroke, thereby drawing blood into the system
from a catheter, is provided to the terminal 156. A withdrawal pump
valve signal at terminal 164 operates the valve 134 (FIG. 2) in
such a fashion as to connect the pump to the 2 milliliter reservoir
130. A blood cup valve signal applied to a terminal 160 causes the
valve 120 (FIG. 2) to operate so as to connect the two milliliter
reservoir 130 to the patient (port 118) rather than to the blood
cup. A sample pH signal is applied to a terminal 410 to indicate to
any apparatus, such as the calculation unit 28 of FIG. 1, that now
is the proper time to sample the output of the pH tester 230 (FIG.
3) at the terminals 240, 242. Similarly, a sample gas signal is
applied to a terminal 412 to indicate to the calculation unit 28,
or such other unit as may be used to analyze the results of blood
tests, that now is the proper time to sample the output of the gas
tester 234 at the terminals 267, 268. A gas/pH valve signal applied
to the terminal 262 in FIG. 4 is connected to both of the terminals
262a and 262b (FIG. 3) so as to cause simultaneous operation of the
valves 226, 260 so as to transfer primary operation from the gas
side to the pH side. A buffer one pump signal applied to a terminal
213 causes the buffer one syringe pump 213 to stroke in the push
direction. A high concentration calibration gas signal applied to a
terminal 310 causes closure of the valve 309 (FIG. 3) to allow the
high concentration calibration gas source 312 to enter the system.
The calibration gas valve signal applied to a terminal 320 causes
the valve 290 (FIG. 3) to transfer from the normal high
concentration connection, as shown, to connect the low
concentration source 330 with the port 288. An H.sub.2 O pump
signal connected to a terminal 212 causes the syringe pump 208
(FIG. 3) to initiate a push stroke. A buffer two pump signal
applied to a terminal 214 causes the syringe pump 210 (FIG. 3) to
initiate a push stroke. A gas blood detector signal applied to a
terminal 270 powers a light source in the blood detector 268' (FIG.
3) so as to be able to detect the presence of blood. Similarly, a
pH blood detector signal applied to a terminal 252 energizes the
blood detector 250 (FIG. 3) so as to be able to detect blood
passing therethrough.
An analysis pump signal is applied to a terminal 414 for
application to the valve 280 (FIG. 3) and to a related valve 416
which is connected in an obvious fashion by tubings 418, 420 to the
pump 294. Thus, with the signal present at the terminal 414 the
valve 280 will connect the valve 260 to the pump 294, and the valve
416 will cause the pump 294 to initiate a pull stroke pulling fluid
through the valve 292 into the pump 294; at this time, operating
air within the pump is exhausted through the tube 418 and the valve
416 through a port 422 to exhaust. Upon removal of the signal on
the terminal 414, the valve 280 connects the port 292 with the port
296 and the valve 416 drives air through the tubing 418 to cause a
push stroke of the pump 294, while operating air therein is
transferred through the tubing 420 and the port 422 to exhaust.
Thus, the pump 294 always draws fluid into itself from the valve
260, and thereafter pushes that fluid through the port 296 of the
valve 280 to liquid waste.
The signal on the terminal 414 is generated specially in FIG. 4 by
means of an AND circuit 426 in response to an Or circuit 427
operated by either one of two OR-invert circuits 428, 430. These
circuits are normally operative because there is normally no signal
present at the terminals 270, 252 so that the blood detectors are
inoperative, and there is also no signals at their output terminals
254, 272. However, once the blood detectors are activated by
signals at terminals 252, 270 these signals preclude the OR-invert
circuit 428 from any longer providing a signal to the OR circuit
427. But if no blood is detected in the blood detectors, then there
will still be no signals at the blood detector output terminals
254, 270 (FIG. 3) so that the related OR-invert circuit 430 will
operate the AND circuit 426 to provide a signal at the terminal 414
for the operation of the pull stroke of the analysis pump 294 (FIG.
3). However, once blood is sensed by either of the blood detectors,
a signal on either of the terminals 254, 272 will cause the
OR-invert circuit 430 to remove the input to the Or circuit 427,
thus terminating the stroke of the pump 294 (FIG. 3). Use of the OR
invert circuit 428 precludes the possibility of noise or other
spurious signals from blocking the AND circuit 426 when the blood
detectors are not turned on. This feature allows drawing just a
requisite amount of blood into the pH tester 230 and the gas tester
234 so the blood isn't drawn through other parts of the system
thereby necessitating a greater amount of blood and washout.
Operation of the device, as illustrated in FIG. 5, begins with the
main power source turned on by the depression of the start switch
380 (FIG. 4) which will cause the latch 376 to become set,
overriding a tendency of the OR circuit 382 to reset it, thereby
closing the normally open switch 348 so as to apply main power to
the 1/6 rpm motor 346. The switch should be depressed for at least
a second until the motor can turn sufficiently so as to clear the
motor control segment and thus remove the signal on the line 381 so
that the motor will continue to run. Then, at time zero, signals
are applied to the terminals 213, 310, 414 and 262 so as to
energize the buffer one pump, close the high concentration gas
valve, start the analysis unit pump 294 and place the gas/pH valve
to the pH side. This causes buffer one to be pushed into the blood
cup 190 and drawn by the constant volume pump into the pH tester
230 all the way into the pump 292, while high concentration
calibration gas flows into the gas tester 234. All of these signals
remain present for thirty seconds. However, after the first second,
the air detectors in the withdrawal unit (FIG. 2) are tested.
Thereafter, at the twenty-first second, signals are applied to
terminals 156, 164 and 160, and the pump in the withdrawal unit
(FIG. 2) is actuated at the same time that the pump valve and cup
valve are actuated so as to draw blood from the catheter through
the connector 32 through the oximeter and the air detector into the
port 88 of valve 90 through the valve 120 and into the two
milliliter reservoir 130. These conditions are maintained for forty
seconds, until about the sixty-first second, although the pump
valve 134 is left in the actuated position to connect the two
milliliter reservoir to the pump all the way to the one hundred
first second. While the blood is being drawn into the withdrawal
unit, at about the twentieth second, all of the elements in the
analysis unit are turned off and there is a ten second
equilibration period where buffer one is allowed to equilibrate
within the pH tester 230. Thereafter, at about the fortieth second,
the pH is sampled at the terminal 240 so as to provide a first
calibration measurement of the pH detector 230. As soon as this is
complete, at about the forty-first second, buffer one is flushed
out of the pH tester 230 by energizing the water pump (terminal
212), reactivating the gas/pH valve so as to feed pH (terminal
262), and reactivating the pump (terminal 414) for a full cycle so
that as water or saline falls into the blood cup, it is drawn all
the way down into the pump. These signals (terminals 212, 262 and
414) are maintained energized for about twenty seconds until about
the sixty-first second.
At the sixty-first second, in the withdrawal unit, the signal on
terminal 156 and that on terminal 160 are removed so that the
withdrawal pump will initiate a push stroke with the valve 120
deenergized so that blood is pushed from the 2 milliliter reservoir
130 into the blood cup. At this time, everything in the analysis
unit is deenergized and remains so for approximately 10 seconds to
allow the blood to settle down in the blood cup. The valve 120 is
actuated after about 7 seconds (which permits pumping substantially
0.4 milliliters into the blood cup) and then it is energized so
that the remainder of the blood will be returned to the patient
along with approximately 1.5 milliliters of saline. It is to be
noted that, prior to starting the operation, saline existed in the
lines as a result of initially loading them or as a result of
finishing the prior cycle as is described hereinafter.
After allowing ten seconds for the blood to settle in the cup, at
about the seventy-first second, the blood detector 250 is turned on
by a signal on terminal 252, and blood is drawn into the pH tester
by applying signals to the terminals 262 and 414 so that the gas/pH
valve is in the pH position and the pump will initiate a pull
cycle. However, as soon as blood reaches the blood detector 250, it
will cause (by means of the apparatus at the bottom of FIG. 4
described hereinbefore) deenergization of the signal at the
terminal 414 so that the pump stroke stops immediately. This
prevents pulling any unnecessary amount of blood beyond the
reference electrode 244. This will occur in something on the order
of eight seconds, and at the end of ten seconds the blood detector
valves 226 and 260 and the primary initialization signal for the
pump 292 are all deactivated. This occurs at approximately the
eighty-first second. Then 20 seconds of equilibration time is
allowed to elapse. During this time, the remainder of the blood in
the analysis unit has been returned to the patient; it should be
understood that since the pump 140 is a constant volume pump,
regardless of the energization thereof, the volume of fluid to be
returned to the patient is determined simply by the length of
stroke so that the pump and relay circuits in the withdrawal unit
are energized simply for a long enough period of time to allow the
pump to complete its stroke. This occurs at approximately the one
hundred and first second.
At this time, the blood in the pH tester 230 is still
equilibrating, as is the high concentration calibration gas which
entered the gas tester 234 at time zero. At the one hundred and
first second or so, the pump in the withdrawal unit (FIG. 2) is
caused to make a pull stroke with the valve 134 disenergized to
pull saline solution from the source 170 down into the pump. At the
same time (one hundred and first second) the pH and gas detectors
are both sampled at the output terminals 240, 242 and 267, 268.
This comprises a first test of the pH of the blood itself and a
first calibration test of the gas electrodes 264. Following that,
at the one hundred and second second, the gas blood detector 268'
is turned on with a signal at the terminal 270 and the pump is
started by applying a signal on the line 414. This action draws
blood from the blood cup 190 down through the gas tester 234 until
the blood reaches the blood detector at which time a signal appears
on terminals 272 which, through the apparatus at the bottom of FIG.
4, removes the signal on line 414 and stops the blood pull stroke.
Then there is a 45 second equilibration period where everything in
the analysis unit (FIG. 2) is turned off. However, at the one
hundred and twenty-first second, flushing of the withdrawal unit
(FIG. 3) begins by shutting off the signal on line 156 to the pump
so that the pump will commence a push cycle and energizing the
valve 134 so that the push will be in the direction of the 2
milliliter reservoir 130. This starts saline (which has just been
withdrawn from the reservoir 170) to flow through the 2 milliliter
reservoir 130 and through the deenergized valve 120 into the blood
cup or waste receptacle. However, after 10 seconds, the valve 120
is energized so that the remainder of the saline then flows
upwardly through the valve 90, the air detector 48 and oximeter 36
toward the catheter. This insures that the lines in the withdrawal
unit are left with saline in them (as referred to
hereinbefore).
Following a 45 second equilibration period with blood in the gas
detector 234, both the gas and pH are sampled at their terminals
240, 242 and 267, 268 which comprise the first sampling of gas in
the blood itself and the second sampling of pH in the blood. The
second sampling of pH is to provide an indication of the integrity
of the gas electrodes 264; if there is any leakage in the gas
electrode 264, such a leak would cause a change in the electrical
potential of the blood in the tubing 232, and because of the
stainless steel electrical connector 236 between that tubing and
the tubing 228, it would also result in a change in the electrical
potential of the blood within the pH electrode 238. This would
result in a different pH reading than that which was previously
obtained. Utilization of a second pH reading of the blood is
achieved by calculations performed in the calculation unit 28 (FIG.
1) or in a computer if one is used, or simply a substantial
difference in pH reading indicates to the operator that there is
likely to be a fault in the gas electrodes 264. This is an
important feature of the present invention.
After sampling the pH and gas electrodes, at about the one hundred
and fifty-sixth second, flushing of the blood from the pH tester
230 and the gas tester 234 commences. This is achieved by closing
the high gas relay 309, energizing the high/low gas valve 290 so
that the low concentration calibration gas is available, energizing
the gas/pH valves 226 and 260 so as to permit flow into the pH side
and starting the pump by applying a signal to the terminals 414.
The high gas valve 309 is closed to permit leakage of gas from the
source 312 into the water source 216 so as to increase the carbon
content thereof. At the same time, saline is drawn from the blood
cup 190 down into the pH tester 230. These conditions continue
until about the one hundred and seventy-sixth second. At that time,
the high gas valve 309 is closed and the pump is turned off so that
it makes a push stroke with the valve 280 deenergized, pumping
blood and perhaps some saline to liquid waste through the port 296.
After two seconds (at the one hundred and seventy-eighth second),
the pump is again turned on drawing more saline into the pH tester
230; during this entire period of time (from the one hundred and
fifty-fifth second) the low concentration calibration gas in the
source 330 has been passing through the valve 290 and the valve 260
upwardly through the gas tester 234 and through the valve 226
upwardly through the port 282 driving blood to waste. At about the
one hundred and ninety-eighth second the pump is again shut off for
two seconds and it pushes the blood and saline which it has drawn
from the pH tester 230 outwardly through the port 296 of the valve
280 to waste. At the two hundredth second, the H.sub.2 O pump is
again energized 212 to cause water to be pushed into the blood cup.
The analysis pump is again started at about the 2 hundredth second
and again draws saline and water through the pH detector for three
seconds, then the valves 226 and 260 are turned off for 2 seconds
so that the pump, instead, draws saline and water into the gas
detector 234. After two seconds the valves 226 and 260 are again
energized so that saline is drawn into the pH detector, and while
this is occurring, the low concentration calibration gas in the
source 330 pushes some of the saline out of the gas detector 234
upwardly through the port 282 to liquid waste. This process
continues until about the two hundred and twentieth second when the
pump is turned off so that it provides a push stroke to push all
the waste it has collected from both the pH tester 230 and the gas
tester 234 outwardly through the port 296 to waste. The procedure
is again repeated so that at approximately the two hundred and
forty-second second the pump again discharges waste that it has
collected from both the pH tester 230 and the gas tester 234,
during which time the valves 226 and 260 have cycled, and while in
the energized position the low concentration calibration gas of the
source 330 has pushed waste upwardly out of the gas tester 234. At
about the two hundred and forty-fourth second, the pump and the
pH/gas valve are again turned on at the same time as the buffer
number two pump is turned on so that buffer number two begins to be
pumped into the blood cup 190 and this is drawn into the pH tester
230. This is completed twenty seconds later, at about the two
hundred and sixty-fourth second. During this 20 second period, the
low concentration calibration gas of the source 312 has been
continuously running into the gas tester 234 and venting outwardly
through the port 282 to waste. Thus at the two hundred and
sixty-fourth second, the pH tester 230 is filled with buffer number
two and the gas tester 234 is filled with low concentration
calibration gas from the source 330. An equilibration period of 45
seconds then passes following which, at the three hundred and ninth
second, both pH and gas are again sampled at their terminals 240,
242 and 267, 268 for a final calibration of both the pH and gas
testers 230, 234. The calibration provides corrections for changes
in sensitivity and drift of the electrodes.
All that now remains is to purge the calibration gas out of the gas
electrode and leave the gas electrode filled with water so as to
prevent the membranes therein from drying out. It is to be noted
that the pH electrode is left with buffer number two residing
therein which prevents it from drying out. The loading of water and
purging of gas in the gas electrode 264 is accomplished, beginning
at the three hundred and tenth second, by energizing the water pump
by means of a signal at the terminal 212 so as to commence to pump
water into the blood cup 190 at the same time that the pump is
operated by providing a signal at the terminal 414 while leaving
the valves 226 and 260 deenergized so that the clean water is drawn
into the gas tester 234. After 20 seconds, the pump is deactivated
for two seconds to allow dumping the mixture of gas and water out
to liquid waste, following which it is again activated to pump the
remaining water out of the blood cup 190 into the gas tester 234.
This completes the operation of the cycle and the motor is caused
to shut off at about the three hundred and fifty-fifth second by
generating a signal on the motor control line 380 which activates
the OR circuit 382 to reset the latch 376, thereby removing the
signal from the normally open switch so that the motor no longer
receives power. The motor will therefore stop when the sixteen
track rotary timer is set on the contact that provides the motor
control signal on line 381.
The embodiment of the invention described hereinbefore thus
provides a very compatible blood withdrawal unit which, according
to the invention, may withdraw blood through lines filled with
saline so as to preserve the integrity of tests to be performed on
blood, or may withdraw blood through lines filled with I.V.
irrigation solutions, thereby to minimize the opportunity for
sodium buildup in the patient. In addition, the described
embodiment provides for final calibration of gas and pH testers
after testing of blood, in addition to initial calibrations before
the testing of blood. By providing a dual test of blood pH, one
without fluid in the gas detector and one with fluid in the gas
detector, together with providing for an electrical connection
between the gas and pH testers, the dual pH tests provide a measure
of the integrity of the gas tester. Carbonation of washout water in
the gas tester provides for the preestablishment of a certain level
of carbonate in the gas detector to reduce the time necessary for
equilibration thereof, and in further accord with the invention,
valving between the pH tester and the gas tester permits
simultaneous washout utilizing a single pump, in combination with
the use of calibration gas to completely flush, forwardly and
backwardly, the gas electrode, while simultaneously performing a
forward flush of the pH electrode.
Although the invention has been shown and described with respect to
a preferred embodiment thereof, it should be understood by those
skilled in the art that various changes and omissions in the form
and detail thereof may be made therein without departing from the
spirit and the scope of the invention.
* * * * *