AN AUTOMATICALLY CONTROLLED, INEXPENSIVE
PUMP-OXYGENATOR

Adrian Kantrowitz, M.D., Stuart Reiner, B.E.E., M.E., and Donald
Abelson, M.D., Brooklyn, N.Y.

Sxe the early reports of the successful development of extracorporeal cir-
culation and open heart surgery,® 14 there has been widespread interest in
refinement of techniques. Our group has directed its energies recently to the
development of an inexpensive, self-controlled pump-oxygenator.

During the 10 years that we have been interested in experimental extra-
corporeal circulation, we have studied various types of pumps’? as well as
bubble oxygenators, screen- and disc-type oxygenators. At present, we prefer
a rotating dise oxygenator which we have modified to suit our particular needs.

The apparatus consists of a rotating dise oxygenator originally suggested
by Bjork’ and more recently, described by Kay and Cross” * #2! and others,?°
combined with a roller-type pump. Venous blood is brought from the superior
and inferior venae cavae to the oxygenator by gravity. Since a venous pump
is not used, a significant source of trauma to the blood is eliminated. The
pool of blood in the oxygenator serves as a venous reservoir so that the latter
component is also eliminated. The discs are driven directly by a small frac-
tional horse power motor at 120 revolutions per minute. Oxygenated blood
leaves at the opposite end of the chamber and is carried by large-bore Tygon
tubing to a roller pump. The pump then returns the blood to the arterial
side through a filter. Excess blood in the opened, bypassed heart is collected
by a suction tip attached to a second roller pump which delivers it to a com-
bined defoaming chamber and bubble trap reservoir. From here, the blood
is returned to the venous end of the oxygenator.

It has been shown by McCaughan and his co-workers!® and others that
most of the trauma to the blood removed from the opened heart results from
excessive mixing of air with the blood in the suction pump. To minimize this
effect, a control button has been placed on the suction handle which is pressed
only when suction is desired. Thus the pump is turned on and off at the table,
and the influx of air is minimized.

 

From the Departments of Surgery, Maimonides Hospital of Brooklyn, and the State Uni-
versity of New York-College of Medicine at Brooklyn.

Supported in part by a grant (H-3023) from the National Heart Institute of the National
Institutes of Health.

Read at the Thirty-ninth Annual Meeting of The American Association for Thoracic
Surgery at Los Angeles, Calif., April 21-23, 1959.

586
Vol. 38, No. 5 AUTOMATICALLY CONTROLLED PUMP-OXYGENATOR 587
November, 1959

The parts of the system which are in contact with blood consist of Tygon
tubing, rubber, stainless steel, and silicone-coated Pyrex glass. <All of the com-
ponents are autoclavable, thus ensuring sterility.

CONTROLS

In most centers where cardiopulmonary bypass is used clinically, the pump-
oxygenator has been operated by either a physician or a specially trained
technician or group of technicians. It is usually necessary to observe several
variables continuously, and make adequate adjustments during the perfusion.
Among the more important factors to be observed and controlled are (1) venous
pressure, (2) arterial pressure, (3) blood level in the oxygenator, (4) flow
rate, (5) blood temperature, (6) replacement of blood loss, and (7) the electro-
eardiogram. Jn addition, some centers routinely monitor (8) the electroen-
cephalogram, (9) arterial and venous oxygen saturation, and (10) blood pH
and pCoQ,.

 

 

 

. 74

ARTERIAL PUMP

  
    
 

 

SUCTION PUMP BLOOD LEVEL
CONTROLLER

DEFOAMING CHAMBER

 

 

  

& BUBBLE TRAP

  

MANOMETER

 

  

 

 

 

 

 

 
 

 

 

VENOUS FLOW
CONTROLLER

Fig. 1.—Schematic diagram of blood flow circuit.

DISC OXYGENATOR al

It is generally agreed that the continuous observation and correction of
the first 7 factors are necessary for a successful perfusion. By using three
control systems, we are able to observe continually and maintain automatically
the first 5 factors at pre-set levels. The technician is able, therefore, to direct
his attention to the replacement of abnormal blood loss, under the direction
of the anesthesiologist. Gibbon® and Kirklin® ? and their associates have de-
scribed the automatic control mechanisms used in the sereen oxygenator which
they employ.

VENOUS PRESSURE

Venous pressures are measured by passing a catheter through a superficial
vein into the inferior vena cava. A sealed mercury manometer is attached to
das KANTROWITZ, REINER, ABELSON cy thoracic and
the end of the catheter. Two electrodes are introduced into one limb of the
mercury manometer and so placed to sense pressures of 10 em. and 12 em. of
water. A motor-driven occluding clamp is placed on the main venous line
between the heart and the input opening of the oxygenator chamber. Since
the oxygenator is placed 75 em. below the heart level, a greater negative pres-
sure is developed at the opening of the venous line than can be used efficiently.
A simple relay circuit is so arranged that if the venous pressure is below 10
em. of water the motor is turned on to clese the clamp 14 of a turn, thus re-
ducing the amount of blood removed from the venae cavae. It then waits &
seconds to see if this adjustment is sufficient to bring the venous pressure into
the ‘‘normal’’ range. If it is not, it will make another correction and again
wait 8 seconds. If the venous pressure is between 10 em. and 12 em. of water
(our arbitrarily selected ‘‘normal’’ range), the motor-driven clamp remains
in a fixed position. If the venous pressure is higher than 12 em. of water, the
circuit turns on the motor-driven clamp to open 14 of a turn, thus removing
more blood from the superior and inferior venae cavae; it then waits 8 seconds
and if the venous pressure has not fallen to ‘‘normal’’ it will then make an-
other adjustment. This mechanism thus assures constant surveillance of the
yenous pressure and automatically adjusts it when indicated to ensure main-
tenance of normal venous pressure. Therefore, the same venous flow that
would normally return to the heart is now being delivered to the pump-
oxygenator.

BLOOD LEVEL CONTROL

Since reliability, autoclavability, and simplicity were the cardinal require-
ments in the design of the volume sensor, a means for obtaining a large output
signal at useful power levels without complicated vacuum tube or transistor
circuitry was sought. Methods that involve weighing the perfusion cham-
ber, level sensors which require floats, or capacitive blood level pickup using
the blood as a dielectric were rejected because of mechanical and electrical
complexity.

A photoelectric blood level sensor was decided upon since it could operate
outside the oxygenator chamber, eliminating cleaning and autoclaving problems.
In addition, the complete generality possible with a photoelectric pickoff per-
mits the direct application to a wide variety of oxygenator chamber designs
with a minimum of modification. A lght source and a light sensitive cell
mounted on the outside of the oxygenator chamber are arranged so that a light
beam passes through the walls of the chamber and falls upon the sensitive sur-
face of a photocell in such a manner that changes in blood level varies the
amount of the light falling on the cell. The electrical output of the cell is then
used to control the speed of the arterial pump motor.

A major factor in the decision to use a photoelectric sensor was the recent
advent of large area cadmium sulfide photocells of great sensitivity and eap-
able of dissipating as much as 0.5 watt of electrical power. The output of
Nuerie. ies AUTOMATICALLY CONTROLLED PUMP-OXYGENATOR 589
such a cell could easily be used to control a simple power amplifier required
for the 14 horse power variable speed pump motor.

The cadmium sulfide cell is a photoconductive cell, that is, the electrical
conductivity of the cell varies with the amount of light falling on it. As a
circuit element, it behaves like a variable resistor. The type 6957 used in this
system is a hermetically sealed unit in which the resistance varies from many
millions of ohms when dark to a few hundred ohms when illuminated. The
purpose of the photoelectric flow controller is to maintain a fixed volume of
blood in the oxygenator throughout the precedure. This state of equilibrium
is achieved by automatically adjusting the speed of the arterial pump which
withdraws blood from the oxygenator. The pumping rate varies in response
to signals from the sensor, the output of which is a funetion of the blood volume
in the oxygenator. An inerease in volume of blood in the oxygenator results

 

Fig. 2.—-Special clamp with photoelectric cell and light source, and electronic control unit.

in an inereased withdrawal pumping rate, and a deercase in volume reduces
the pumping rate. The photocell is thus able to ‘‘wateh’’ the blood level changes
in the oxygenator precisely. In the 17-inch dise oxygenator, an increment of
90 ¢.c. of blood is detectable by the photocell. The electrical system is damped
and is extremely stable. The photocell tends to select the correct pump speed
continuously and maintain this speed at all times. The arterial pump output
is determined by the venous return to the oxygenator. The venous return, as
has been described earlier, is selected automatically to maintain venous pres-
sures at normal levels. The blood level, then, in the pump-oxygenator is
effectively locked and thus (barring abnormal blood loss from the entire system)
ensures against undesirable shifts in the patient’s blood volume® ” 1% and auto-
matically maintains blood pressures within normal ranges. Normal arterial
590 KANTROWITZ, REINER, ABELSON cf; Thoracig and
pressures assure flow rates which are consistently above 100 ec. per kilo per
minute. Thus, this one sensing device and control mechanism automatically
maintains the blood in the machine at pre-sct. volumes, the flow rates above 100
c.c. per kilo per minute, and the arterial pressures within the normal range.
Falling arterial pressures indicate abnormal blood loss from the entire
system. Blood replaced into the oxygenator will then be delivered immediately
to the patient, and arterial pressure will return to the normal range. Provision
is made for quickly switching the control to manual operation in ease of failure,

 

Fig. 3.—Special clamp with photoelectric cell and light source mounted on oxygenator.

by disconnecting the cell and substituting a variable resistor. The only com-
ponents in the controller having finite life are two thyratrons and the excitor
lamp. The thyratrons used have sufficient capacity so that if one fails, the
system will continue in operation. The possibility of both thvratrons failing
simultaneously is remote. Failure of the excitor lamp will cause the pump to
run at full speed. In this event, the control is switched to manual operation
for the remainder of the perfusion. Two excitor lamps could be built into
the lamp housing for additional safety. This controller should have excellent
reliability and should not be subject to sudden failure since it is simple in
design and contains components that inherently have long life.

BLOOD TEMPERATURE CONTROL

It has been shown by De Wall and others that it is desirable to maintain
the blood in the extracorporeal circuit close to normal body temperatures.
First, rapid changes in blood temperature tend to promote hemolysis of blood,
Vol. 38, No, big AUTOMATICALLY CONTROLLED PUMP-OXYGENATOR 591
and second, oxygen is more soluble in blood at lower temperatures than at
higher body temperatures. Therefore, it is possible that a saturated solution
of oxygen in cooler blood in the oxygenator may come out of solution in the
form of small bubbles when the blood is returned to the patient and becomes
warmed. A thermistor probe is placed in a thin-walled pocket in the oxygenator
chamber below the blood level. The temperature of the blood is then sensed
by the thermistor and controlled by a commercially available temperature
switch which turns a heater coil on and off. We have set the controller to 38°
C. and are able to maintain the blood temperature within 0.5° C. The controller
itself can detect changes of 1/10 of a degree centrigrade.

 

Fig. 4.—Completely assembled automatically controlled pump-oxygenator.

TECHNIQUE OF PERFUSION

The pump-oxygenator is primed with 2,500 ««. of blood. This amount is
sufficient to fill the oxygenator, the combined filter and bubble trap, the de-
foaming chamber, and all of the lines. Blood is cireulated for a few minutes
in order to be certain that all air bubbles have been removed. The arterial
pump motor is turned off by a switch. The artcrial and venous lines are then
clamped and appropriate connections are made to the paticnt. To start the
perfusion, the clamps are removed from the venous and arterial lines and the
arterial pump motor switch is turned on. From that point on, the pump-
oxygenator regulates itself. When the tourniquets around the superior and
a92 KANTROWITZ, REINER, ABELSON J. Thoracic and

Cardiovas. Surg.
inferior venae cavae are tightened to initiate total bypass, the increased venous
return to the pump-oxygenator is automatically compensated for and all of
this blood immediately returned to the patient after oxygenation. To discon-
tinue the perfusion, one needs only to clamp the venous line. Venous return
to the pump-oxygenator is then discontinued and the arterial pump will come
to a stop as soon as the blood level in the oxygenator reaches its priming posi-
tion.

DISCUSSION

It seems axiomatic that if a mechanism can be made to perform a given
function more reliably than a human being that it should be used. A practical
consideration that often enters in such a decision is the eost of such an appa-
ratus. All of the cleetronie controls in our pump-oxygenator ean be purchased
for under $1,000.* The technician who stands by during the bypass has to
be available in case of mechanical or electrical failure, in which case the pump-
oxygenator can be run by manual controls. Otherwise, after the initial filling
of the oxygenator with priming blood, he ean devote his entire attention to
replacement of unusual blood loss under the direction of the anesthesiologist.

Adjustments during the perfusion are automatically sensed and made by
the machine during critical periods of change. When the perfusion is first
begun, there is a tendency for the pump to overtransfuse the patient. When
the venae eavae are occluded, an inereased amount of blood is usually returned
to the pump-oxygenator. Conversely, when the tourniquets are released, large
amounts of blood can suddenly be lost from the machine. If there is unusual
blood Joss from the patient during the bypass, there is a tendeney for blood
to be lost from the pump-oxygenator. If vasopressor drugs are given, blood
has a tendency to rise in the oxygenator. We feel that these abnormal shifts
in blood volume are deleterious to the patient on bypass and are avoided when
the blood volume in the machine is maintained at a constant level. Decreased
blood level in the oxygenator decreases the efficiency of the oxygenating sur-
face and, if the level drops low enough, may lead to air embolism. If the blood
in the oxygenator rises too high, it may wet the shaft, leading to turbulence
and foaming, or leak out of the shaft bearing. The apparatus that we have
designed eliminates the possibility of the occurrence of these untoward mani-
festations.

SUMMARY
1. An improved, automatically controlled, rotating dise pump-oxygenator is
described.

2. Venous pressures are continuously monitored and automatically con-
trolled during bypass by the use of a motor-driven clamp on the venous line.

3. Blood levels, arterial pressures, and blood flows are automatically sensed
and controlled with one device which is rugged, reliable, and inexpensive.

*Available from the Teca Corporation, 80 Main Street, White Plains, N. Y.
Vol. 38, No, § AUTOMATICALLY CONTROLLED PUMP-OXYGENATOR 593

November, 1959

4. Blood temperatures in the oxygenator are also controlled automatically.

The authors wish to express gratitude to Mr, Percival Henry and Mr. Marco Albanese

for their valuable technical assistance.

10,
ii.
12.

9

Oe

14.

46.

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. Cross, F. &., Berne, R. M., Hirose, Y., Jones, R. D., and Kay, KE, B.: Deseription and

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