Blood oxygenator utilizing a removable membrane oxygenator unit

An oxygenator for blood which comprises means for removably holding a membrane oxygenator unit, means for conveying blood to a patient through the oxygenator unit in a first flow path and back to the patient, and means for supplying oxygen gas through the oxygenator unit in a second flow path separated from the first flow path in the unit by a semi-permeable membrane. The oxygenator unit holding means carries a plate which has an oxygen inlet manifold port positioned to communicate with a mounted oxygenated unit, to provide a sealed oxygen flow path through the plate into the oxygenator unit and to provide for dispersal of effluent oxygen in a plurality of directions, thereby preventing the accidental obstruction of the oxygen outlet of the unit.

BACKGROUND OF THE INVENTION 
Membrane oxygenators for blood are attracting growing medical interest 
because of their capability of partially or completely taking over the 
respiratory function of a patient for a period of many hours and even days 
without unacceptable damage to the blood supply. Previously, bubble-type 
oxygenators involving the direct application of oxygen bubbles through a 
stream of blood had been used in open heart surgery for periods up to four 
or five hours. However, unacceptable damage frequently is inflicted upon 
the blood supply of the patient if the bubble oxygenators remain in 
operation for periods significantly longer than this. 
Commercially available disposable membrane oxygenator units are disclosed 
in U.S. Pat. No. 3,757,955. The same patent describes a membrane 
oxygenator unit currently under development in which the membrane is made 
of a porous, hydrophobic material such as 3 or 4 mil 
polytetrafluoroethylene sheeting having an effective pore diameter of 
about 0.5 micron. Such materials are capable of rapidly transferring 
oxygen, carbon dioxide and water vapor, while preventing the transfer of 
blood itself through the membrane. Porous membrane oxygenator units 
exhibit an oxygen and carbon dioxide transfer capability which greatly 
exceeds the older membrane oxygenator unit designs which utilize thin 
silicone rubber membrane and the like. Accordingly, porous membrane 
oxygenator units can support the total respiratory needs of a patient with 
a significantly smaller total surface area of membrane than a conventional 
silicone rubber membrane oxygenator unit of similar design. As a result of 
this, the amount of blood which is removed from the body at any one time 
can be typically less with porous membrane oxygenator units, which is a 
significant and important advantage. 
There is, however, a drawback to porous membrane oxygenator units: it is 
absolutely necessary for the pressure on the blood side of the membrane to 
at all times equal or exceed the pressure on the gas side of the membrane. 
If these conditions fail, the increased gas pressure may drive gas bubbles 
through the membrane into the blood flow path, from where the gas bubbles 
may be conveyed back to the patient. This could create a life-threatening 
embolism in the patient. 
Accordingly, in U.S. patent application Ser. No. 390,567 filed Aug. 22, 
1973 by Ronald J. Leonard, an oxygenator apparatus is provided for the 
safe and effective utilization of hydrophobic, porous membrane blood 
oxygenator units. In the device described in the patent application, a 
manometer means is provided to assure safe and reliable limitation of the 
gas pressure in the oxygenator unit. 
Also, the aforesaid application discloses heat exchanging means and the 
like for maintaining the appropriate blood temperature and other desirable 
parameters of operation. 
For the commercial manufacturer of porous membrane blood oxygenator units, 
it is a matter of great importance to be certain that the customers 
utilize the oxygenator unit in a correct manner, using the correct 
equipment for mounting and supplying blood and oxygen to the membrane 
oxygenator unit, so that there will be no dangerous gas overpressure, 
driving oxygen bubbles into the blood path, which can instantly create a 
life-threatening situation. 
In accordance with this invention, an oxygenator and membrane oxygenator 
unit for use therein are provided in which the membrane oxygenator unit is 
used only with great difficultly apart from the oxygenator itself, which 
can be designed to provide the necessary parameters of operation that 
result in safe use. Accordingly, a relative foolproof system is provided 
for the protection of patients. 
Furthermore, in accordance with this invention, a system is provided for 
assured, unrestricted exhaust of gas, to prevent any obstruction of the 
flow of gas from the oxygenator unit, thus avoiding a consequent, 
potentially disastrous rise in the gas pressure of the oxygen flow path in 
the oxygenator unit. 
DESCRIPTION OF THE INVENTION 
The blood oxygenator of this invention comprises means for removably 
holding a membrane oxygenator unit, and means for conveying blood from a 
patient through the oxygenator unit in a first flow path and back to the 
patient. The oxygenator also has means for supplying oxygen gas through 
the oxygenator unit in a second flow path separate from the first flow 
path and separated from it in the oxygenator unit by a semi-permeable 
membrane. In accordance with this invention, the means for holding the 
oxygenator unit is adapted to carry a plate in a position to engage an 
oxygenator unit installed in the holding means of the oxygenator. The 
plate defines an oxygen inlet manifold port positioned to communicate, 
while engaged with the oxygenator unit, with the inlet of the second flow 
path of the oxygenator unit, to provide a sealed oxygen flow path through 
the plate into the oxygenator unit. 
As a result of this arrangement, oxygen comes to the plate by means of an 
oxygen line, and is manifolded or spread into a wide flow path for 
delivery to the individual oxygenator unit flow channels by means of parts 
carried by the oxygenator itself rather than the oxygenator unit. As a 
result of this, oxygenator units desired for use with the device of this 
invention do not carry an oxygen manifolding means, and thus are not 
conveniently used with makeshift equipment. Hence, the user of a 
disposable oxygenator unit is strongly encouraged to utilize the standard 
equipment for that unit with its tested safety features, rather than to 
inconveniently improvise his own arrangement of apparatus. 
A typical membrane oxygenator unit defines blood and oxygen flow paths 
comprising a plurality of interleaving parallel channels. It is 
contemplated that the typical oxygenator units for use in accordance with 
this invention will have a wide mouth opening for inlet of oxygen and 
outlet of spent gases to and from the oxygenator unit, with the inlets and 
outlets of the parallel, interleaved oxygen channels in the oxygenator 
unit being directly exposed to the exterior of the unit through the wide 
mouth openings. The manifold port on the plate of the blood oxygenator is 
accordingly proportioned to surround and seal the wide mouth opening 
around the inlets of the parallel channels, to provide the sealed oxygen 
flow path. The wide mouth opening of the oxygen inlet to the membrane 
oxygenator unit prevents the simple attachment of an oxygen line to the 
oxygenator unit, and thus encourages the use of the standard oxygenator 
equipment especially manufactured for use with the membrane oxygenator 
unit, which will include the necessary safety features such as a means for 
limiting gas pressure, a heat exchange unit, and the like. 
Furthermore, in position of use the plate, with the exception of the 
manifold port area, is spaced from the membrane oxygenator unit in a 
position to overlie the gas outlet port of the second flow path of the 
oxygenator unit. Accordingly, oxygen gas escapes through the outlet port, 
then passing in many directions of flow between the oxygenator unit and 
the plate to the exterior. The advantage of this is that such arrangement 
greatly reduce the possibility of some accidental obstruction of the gas 
outlet port, such as might take place if the outlet port were a simple 
tube or opening. The reason this is necessary is that the accidental 
placement of some obstructing object, even momentarily, in front of the 
gas outlet port during operation could cause a sudden rise of gas pressure 
within the membrane oxygenator unit, which is dangerous for reasons 
discussed above.

Referring to the drawings, an oxygenator is shown which comprises, means 12 
for removably holding a membrane oxygenator unit 14. Means for conveying 
blood from a patient through the oxygenator in a first flow path and back 
to the patient are also provided. Blood in inlet tube 16 is propelled 
through the oxygenator by a conventional roller pump 20, being drawn out 
of the venous reservoir 22. Blood is supplied to the venous reservoir 
through conduit 24 from the patient's venous supply. 
Downstream from the oxygenator, blood passes from the oxygenator into blood 
outlet tubing 18, and from there through heat exchanger 26 (such as 
disclosed in U.S. Pat. No. 3,640,340), to arterial reservoir 28 by tube 
19, from where it is propelled by a second roller pump 30 into the 
patient's arterial blood supply through conduit 32. Heat exchanger 26 is 
mounted on bracket 27 with its heat exchange fluid flow path inlet and 
outlet in communication with ports 29, which pass through bracket 27 of 
holder 12 for connection with a heat exchange fluid source. 
A cardiotomy reservoir 34 can be provided to receive blood from a 
cardiotomy sucker which sucks blood from the patient's incision site or 
the like, and passes it to the reservoir through line 36. The cardiotomy 
reservoir is connected by line 38 to a filter 40, which in turn connects 
with the venous reservoir 22. 
Unit holding means 12 is held by bracket 35, which in turn carries a mast 
37 having hangers 39, 41 for removably holding bood containing components 
of the oxygenator. Bracket 35 is in turn held on a hanger 43 which is 
attached to supporting member 45. 
Referring also to FIGS. 2 through 5, details of oxygenator unit holder 12 
and related parts are shown. 
Holder 12 is shown to carry an oxygenator unit engaging plate 42, which in 
turn defines an oxygen inlet manifold port 44 which terminates at its 
inner end with an O-ring seal 46. A source of oxygen gas is provided 
through oxygen inlet line 48 to communicate with oxygen inlet manifold 
port 44, which provides a sealed oxygen flow path through the plate into 
the oxygenator unit. 
Recessed portion 50 within O-ring 46 is provided to permit the oxygen gas 
to freely flow throughout the entire interior of O-ring seal 46. 
Inlet manifold port 44, O-ring seal 46, and recessed portion 50 are 
positioned to communicate in sealing relation with the oxygen inlet 52 of 
oxygenator unit 14 as shown in FIGS. 3 and 5. As can be seen from FIG. 3, 
oxygen inlet 52 is elongated so that the many inlet ends of parallel flow 
channels 54 of conventional oxygenators are all directly exposed to the 
exterior of the oxygenator unit through inlet 52. O-ring seal 46, as part 
of the manifold port of plate 42, is proportioned to surround and seal 
inlet 52 of oxygenator unit 14 to provide a sealed oxygen flow path when 
unit 14 is installed in holder 12. 
Oxygen flow path outlet port 56 of unit 14 is also typically elongated to 
permit the free exit of surplus oxygen gas, plus carbon dioxide and water 
vapor which is passed into the second flow path of oxygenator unit 14. 
In FIG. 5, a typical construction of the layers which define flow paths 54 
is shown. Porous, semi-permeable membrane 14H overlies support screening 
14S is a convoluted, multilayer arrangement as further illustrated in U.S. 
Pat. No. 3,757,955. The edges of the membrane and screening are sealed 
together by a line of cured potting compound 14P, and the structure is 
encased between walls 15, which are held together by fasteners 17 (FIG. 
3). 
As shown in FIG. 4, oxygenator unit engaging plate 42 is positioned to be 
spaced from and define an unbroken wall 58 over gas outlet port 56 of the 
oxygenator unit in position of use and separated by space 59, which is 
typically about 1/8 inch wide. As a result of this, exhaust gas from 
outlet 56 has unrestricted exit in a plurality of directions through space 
59 between plate 42 and unit 14. The result of this is to greatly reduce 
the probability of accidental obstruction of outlet 56, since gas will 
vent adequately from oxygenator unit 14 as long as any substantial portion 
of elongated space 59 remains open to the exterior. 
Plate 42 is attached to holder 12 by a removable nut 60 at one end and 
conventional detent means 62 at its other end, so that plate 42 is easily 
removable from holder 12. 
Line 64 and conduit 65 through cover 70 provide communication between the 
oxygen inlet manifold port 44 and safety means 66, held by bracket 27, for 
preventing the pressure of oxygen gas in the inlet manifold port from 
reaching a level sufficient to cause gas bubbles to pass through the 
porous, semipermeable membrane 14m of oxygenator unit 14. This safety 
means 66 comprises a liquid-filled tube having a rigid, tubular extension 
68 of line 64, which safety means functions as a pressure limiting device 
in the manner described in U.S. Pat. application Ser. No. 390,567, filed 
Aug. 22, 1973 by Ronald J. Leonard and now U.S. Pat. No. 3,927,980 issued 
Dec. 23, 1975. 
Oxygenator unit holder 12 also comprises top and bottom plates 12p, 12q, 
and side walls 12s, which are secured together in the manner previously 
described for plate 42, by means of nuts 12n which fit on bolts 12b, and 
detent means 12d. Plate 12p is attached by glueing or welding to bracket 
35. Oxygenator unit 14 is optionally not enclosed along its rear, blood 
flow side. 
In the specific embodiment shown herein, inlet manifold port 44 does not 
pass straight through plate 42, bt makes two right angle turns as shown in 
FIG. 4 so as to pass through a U-shaped heater block 69 which is mounted 
within cover 70 which, in turn, is carried by plate 42. Heater block 69, 
through which inlet manifold port 44 passes as an elongated channel, 
provides means to warm the oxygen gas entering into the oxygenator unit to 
a predetermined temperature. A typical heater block 69 usable herein can 
be a typical 45 watt, 120 volt, 3-ohm electric cartridge heater. Conduit 
65 also passes through heater block 69 to communicate with manifold port 
44 therein. 
Heater block 69 is controlled by two thermostats 72, electrically connected 
together so that the disconnection of either thermostat deactivates heater 
block 69. The purpose of this is to provide a high degree of assurance 
that the oxygen gas is not overheated, since oxygen gas temperatures in 
excess of 42.degree. C. could cause serious damage to blood in the 
oxygenator. Fuse 73 is also provided for added safety. 
Insulating wall 74 prevents undue heat loss from heater block 69. If 
desired, an alarm means can be provided to activate alarm buzzer 78 when a 
pressure switch 79 mounted in fluid communication with the inlet manifold 
port 44 is not sensing a gas pressure in excess of a standard pressure of 
at least 6 inches of water, which is equivalent to approximately 5 liters 
per minute of oxygen flow through port 44 when the port diameter is about 
one-fourth inch. This arrangement may comprise a conventional relay 80 
activating buzzer 78 when the predetermined gas overpressure is not 
sensed. 
Port 82 is defined completely through plate 42 and cover 70 to permit the 
passage of inflation line 84 of oxygenator unit 14 therethrough. Inflation 
line 84 communicates with an inflatable shim inside of oxygenator 14 which 
can be used to pressurize the screening layers 14s and membrane layers 14m 
together to counter-balance the tendency of the oxygenator unit to expand 
due to the blood pressure pushing the screening and membranes apart. 
The inflatable shim may be placed at the midpoint of the stack of screening 
and membrane layers, or it can be of U-shaped cross-sectional construction 
to provide a pair of expansion members on each side of the stack for the 
same purpose. Other designs of inflatable shim can also be used. 
Typically, unit holder 12 is positioned at an angular relationship to the 
vertical by bracket 35, to elevate the blood outlet as shown in FIG. 4, to 
facilitate the priming of the oxygenator unit with blood or saline 
solution. The angular relationship facilitates the removal of all air 
bubbles from the oxygenator unit into outlet line 18 during priming. 
Bottom plate 12q has a beveled lower edge 86 so that unit holder 12 
assumes the same angular relationship to the vertical when resting on a 
horizontal surface, before being hung by bracket 35 on arm 43. Thus, unit 
holder 12 can be conveniently loaded with an oxygenator unit, and the unit 
primed with saline solution, prior to hanging on arm 43. 
The above has been offered for illustrative purposes only, and is not 
intended to limit the invention of this application which is as described 
in the claims below.