1470 MAGOVERN ET AL ECMO WITH POSTCARDIOTOMY CARDIOGENIC SHOCK

Ann Thorac Surg 1994;57: 1462-71

So when using the device, it is basically an all or nothing phenomenon. You keep flow at 4 L/min, look at the transesoph- ageal echocardiogram, reduce the flow quickly, look at the heart, and then basically just go for it. If it looks like the heart is going to pick up enough energy and support the circulation, then you take the device out, but if it looks questionable, then you have to keep it in for an indefinite amount of time.

We also had four oxygenator failures, and in those cases we saw foam developing in the oxygenator itself. However, this was

not associated with falling levels of O2 tension or rising levels of CO, tension. It was a progressive deterioration in the oxygen- ator, and we were able to replace it in those 4 cases without any difficulty.

With regard to left ventricular distension in the mitral valve patients, the idea of putting in a vent through the left ventricle is attractive, but I have not yet determined the implications of doing so. It certainly raises the specter of air embolism and, again, stroke and clot in the vent catheter.

INVITED COMMENTARY

One of the axioms of extracorporeal circulation, known to perfusionists as Zwischenberger #1, is ”There ain’t nothin like venoarterial bypass.” Magovern and col- leagues have demonstrated that once again in a report of 21 patients with postcardiotomy cardiogenic shock treated with venoarterial bypass, which they refer to as extracor- poreal membrane oxygenation (ECMO). This report adds to the 187 patients collected by Jon Hill and associates [ l ] from Portland and the 866 patients recorded in the Extra- corporeal Life Support Organization Registry [2]. Magov- ern and associates report 52% survival (11 of 21 patients) and 79% survival in the best-risk patients (12 of 14). These results are better than their prior experience with a centrifugal pump alone used as a ventricular assist device (36% survival in 80 patients). The support system used to establish venoarterial bypass in all of these reports is (1) right atrial cannulation (directly or via an extrathoracic vein) draining directly to a (2) servoregulated pump without a reservoir to a (3) membrane oxygenator, (4) heat exchanger, and (5) arterial cannula in the aorta (directly or via an extrathoracic artery). This system is managed using (6) minimal or no heparin, (7) normothermia, (8) blood products for bleeding or coagulopathy, and (9) continu- ous monitoring in the intensive care unit.

This approach is commonly referred to as ECMO, although extracorporeal life support (ECLS) is a better description of this technology. Extracorporeal life support differs from operating room cardiopulmonary bypass (CPB), which includes (1) a large venous reservoir, (2) infinite anticoagulation with heparin, usually (3) hypo- thermia, (4) continuous bleeding and autotransfusion, (5) hemolysis, and usually (6) hemodilution and anemia. Conventional CPB certainly uses venoarterial bypass, but every cardiac surgeon knows that supporting a heart that will not take over in the operating room for more than a few hours leads to progressively more bleeding, edema, systemic organ failure, acidosis, even worse cardiac func- tion, and death in 6 to 12 hours. Extracorporeal life support is also venoarterial bypass but maintains normal systemic physiology, alert mental function, minimal bleeding when properly managed, and routine survival in patients of all ages, even when used for days or weeks. Even newborn infants, so difficult to maintain on CPB for a few hours, are managed with ECLS for days without

complications in neonatal intensive care units. When the circuit is changed to ECLS after a long CPB run, the bleeding is controlled, acidosis clears, and patients regu- larly survive if the injured organ recovers, as demon- strated once again by Magovern and associates. Why the remarkable difference? Obviously the answer lies in com- ponents of the technique unique to CPB as commonly practiced: reservoirs, total heparinization, nonstop au- totransfusion, hypothermia, and hemolysis. Extracorpo- real life support (or the system called ECMO by Magovern and associates) is simply venoarterial CPB without the lethal components. There is an important lesson here for cardiac surgeons and perfusionists.

It is plain to see why ECLS is more effective than CPB for long-term life support, but why would ECLS be better than left ventricular or biventricular assist device systems, as suggested by Magovern and associates? The only major differences are inclusion of a membrane oxygenator be- tween the pump and the arterial line, and (in most cases) the personnel, philosophy of management, and setting of ECLS. The membrane oxygenator serves at least two crucial functions: precise control over the gas composition of perfusate blood and a very effective filter for macro and micro particles larger than approximately 100 pm (in contrast to conventional arterial line filters with a pore size of 20 to 40 pm). The team, approach to management, and setting with ECLS are equally important factors. Extracorporeal life support is managed in the intensive care unit, where it is expected to run for days or weeks, with no pressure to make the room or team available for the next surgical case. If the heart does not recover in 12 to 24 hours this is viewed as standard practice, not a reason to quit. The “ECMO team” is a combination of physicians, nurses, perfusionists, and ECMO specialists skilled and experienced with this method of venoarterial bypass, with different expectations and practice patterns than the operating room CPB team. The approach to management includes several aspects of operating room perfusion such as control of flow by venous saturation monitoring, judging how much partial support is ade- quate, and individual attention to right ventricular, left ventricular, and pulmonary function. Standard ECLS practices such as normothermia, awake patients, minimal anticoagulation, and preventing hemolysis and anemia

Ann Thorac Surg 1994;57 1462-71

MAGOVERN ET AL 1471 ECMO WITH POSTCARDIOTOMY CARDIOGENIC SHOCK

should be standard practice with left ventricular or biven- tricular assist devices but are often misunderstood or ignored when mechanical support is used for a few days. It is not unusual to find a patient on a ventricular support system 24 hours after a cardiac operation with borderline pulmonary function despite hefty ventilator settings, plasma hemoglobin level greater than 30 mg/dL, total hemoglobin level less than 10 g/dL, and venous saturation in the 50% range, with steady bleeding and the picture of consumption coagulopathy despite minimal hepariniza- tion. If these conditions exist, something is not right with the approach to management. Interestingly, groups that report regular success with prolonged use of mechanical left ventricular or biventricular assist devices have learned how to solve these problems. It should be noted that centrifugal pumps cause major hemolysis in ventricular assist or ECLS applications whenever the venous line is partially or temporarily occluded (see Tamari and co- workers [4]), as demonstrated in Magovern and associ- ates’ report. Servoregulated roller pumps prevent this problem.

Magovern and associates attribute the success in their series to the Carmeda system of topical heparin bonding. I agree that permanent heparin bonding is a major ad- vance and clearly minimizes the early surface-induced phase of blood component activation. I would like to believe that the use of the Carmeda Bioactive Surface is a major contributor to the success of ECLS in this series, but it is probably not the case. The amount of bleeding from Magovern and associates’ patients (average, 21 units in 2 days), and the amount of platelet transfusion (average, 28 units in 2 days) is exceptionally high compared with my usual experience with uncoated circuits. They did not tell us what level of activated clotting time was maintained, nor did they report oxygenator failure. Our usual practice is to titrate very low heparin doses to maintain activated clotting time around 150 seconds in these patients; bleed- ing occurs but is manageable, embolism is very rare, and oxygenator failure is very rare using solid silicone rubber Avecor membrane lungs. I agree that the Medtronic Maxima microporous oxygenator used by Magovern and associates is ideally suited for emergency application because it is quick and easy to prime and has very efficient gas exchange. However, any of the currently available

microporous oxygenators will develop plasma leakage and fail in 1 to 4 days. The continuous hemolysis (plasma hemoglobin level, 70 to 80 mg/dL) in Magovern and associates’ series is probably caused by the centrifugal pump. Finally, even though it is probably desirable to use coated surfaces that minimize blood component activa- tion, all the evidence from 10,000 cases of ECLS for respiratory support suggest that what Magovern and associates call ”enzymatic chaos and the whole body inflammatory response” is not very important after the early phase of blood surface contact.

All of these comments are brought up as food for thought, not criticisms of Magovern and associates’ re- port. Certainly 50% overall survival and 79% survival in good-risk patients are very impressive results. I hope it will prove to be true that heparin-bonded surfaces and microporous oxygenators will improve all of our results with these cases. I have not addressed other issues such as left atrial venting, choice of inotropes, afterload reduc- tion, management of the open chest, or reoperation for bleeding. These and dozens of other details must be carefully attended to in the management of these patients. Nonetheless, the basic premise is still true: “There ain’t nothin like venoarterial bypass.”

Robert H . Bartlett, M D

Department of Surge y University of Michigan Medical Center 2920 Taubman Center, Box 0331 1500 E Medical Center Dr Ann Arbor, MI 48109-0331

References 1. Hill JC, Rruhn PS, Cohen SE, et al. Emergent applications of

cardiopulmonary support: a multiinstitutional experience. Ann Thorac Surg 1992;54:699-704.

2 Stolar CJH, DeLosh T, Bartlett RH. Extracorporeal life support organization 1993. ASAIO J 1993;39:976-9.

3. Tamari Y, Lee-Senfiba K, Leonard ES, Pamell V, Tortolani AJ. The effects of pressure and flow on hemolysis caused by BioMedicus centrifugal pumps and roller pumps: guidelines for choosing a blood pump. J Thorac Cardiovasc Surg 1993; 106:997-1007.