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Ann Thorac Surg 2001;71:210-214
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

When to discontinue extracorporeal membrane oxygenation for postcardiotomy support

^a Department of Thoracic and Cardiovascular Surgery, University of Virginia Health Sciences Center, Charlottesville, Virginia, USA

Accepted for publication August 21, 2000.

Address reprint requests to Dr Kron, Department of Thoracic and Cardiovascular Surgery, University of Virginia Health Sciences Center, Box 3111, MR4 Building, Charlottesville, VA 22908
e-mail: ikron{at}virginia.edu

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Background. Extracorporeal membrane oxygenation (ECMO) has demonstrated limited success in adult postcardiotomy shock. The goal of this study was to determine when to discontinue ECMO for postcardiotomy support.

Methods. During a 7-year period ECMO was used in 51 postcardiotomy patients, of whom 16 (31%) weaned and 8 (16%) survived.

Results. Patients in the heart transplant group were more likely to wean compared with patients in the non–heart transplant group (p = 0.03). Patients aged greater than 65 years (p = 0.04) or with ejection fractions of less than 30% after 48 hours of ECMO (p < 0.001) were less likely to wean. Time on ECMO was significantly longer for survivors in the heart transplant group (101.3 ± 7.5 hours) compared with survivors in the non–heart transplant group (28.3 ± 11.9 hours, p < 0.001).

Conclusions. After 48 to 72 hours, consideration should be given to discontinuing ECMO, either by moving to an implantable ventricular assist device or by withdrawal of support, except in those patients with heart transplants. In the latter, both severe postoperative pulmonary hypertension and reperfusion injury may take as long as 120 hours to reverse.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Although advances in surgical technique, cardiac anesthesia, and myocardial protection have reduced adult postcardiotomy cardiogenic shock over the past decade, 0.5% to 1% of all postcardiotomy patients will have severe cardiac failure after cardiopulmonary bypass (CPB) that is refractory to inotropes and intraaortic balloon pumps [1–3]. Extracorporeal membrane oxygenation (ECMO) provides a temporary means of support in these patients as well as in those with delayed shock. Institution of ECMO allows time for myocardial recovery in those with "stunned" myocardium. Patients with postcardiotomy cardiogenic shock secondary to irreversible myocardial injury, however, are unlikely to have the same benefit from ECMO [4, 5]. Furthermore, prolonged ECMO can be detrimental. Complications such as bleeding, stroke, renal failure, and respiratory insufficiency limit support duration and contribute to a high morbidity and mortality in adult postcardiotomy patients [2, 6, 7].

Patients undergoing heart transplantation may require postoperative ECMO support for additional circumstances. Reperfusion injury from heart preservation can cause primary graft dysfunction and cardiogenic shock [8, 9]. Patients with heart transplants can also have significant pulmonary hypertension in the early postoperative period that is refractory to pulmonary vasodilators such as inhaled nitric oxide, resulting in right ventricular overload and heart failure [10–12]. Both of these clinical scenarios can be temporarily overcome with ECMO.

Many postcardiotomy patients are ultimately unable to wean from ECMO support. Early recognition of these patients may be useful. Prompt use of implantable ventricular assist devices (VADs) in those patients with nonrecoverable cardiogenic shock could reduce mortality and complications of prolonged ECMO while providing a chance for subsequent heart transplantation [5]. The ability to predict outcome could also prevent prolonged ECMO in those who are unable to wean and are not heart transplant candidates. The goal of this study was to outline a mechanism for deciding when to discontinue ECMO in postcardiotomy patients.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Patient population, data collection, and statistical analysis
From January 1, 1993, to January 1, 2000, a total of 5,600 adult patients ( 18 years of age) had open cardiac procedures requiring CPB at our institution. Of these patients, 51 (0.9%) required postcardiotomy ECMO. The average patient age was 61.0 ± 1.7 years (range 32 to 77 years). There were 29 (57%) male and 22 (43%) female patients.

For patients undergoing heart transplantation, donor harvest was performed using Euro-Collins preservation solution. Donor hearts were appropriately size matched for recipients based on body weight. For patients with heart transplants who were placed on ECMO, heart size at time of transplant appeared to be appropriate for the recipient. Data for this study were collected from patients’ hospital charts and ECMO records. Student’s t and Fisher’s exact tests were performed to compare variables. Data are expressed as mean ± standard error of the mean (SEM). A p value of 0.05 or less was considered to be significant.

Device
The ECMO system at our institution is comprised of a heparin-bonded Carmeda BioActive Surface circuit, a Maxima Plus PRF (plasma resistant fiber) hollow membrane oxygenator with integral heat exchanger, and a Biopump centrifugal blood pump (circuit, oxygenator, and pump from Medtronic Cardiopulmonary, Anaheim, CA); an oxygen/air blender (Sechrist, Anaheim, CA); and a Blanketrol II Hyper-hypothermia heater/cooler (Cincinnati, OH). Patients who failed to come off CPB after cardiac surgery had ECMO instituted with the previously inserted CPB catheters. For patients requiring delayed transthoracic ECMO after successfully weaning from CPB, the right atrium was cannulated with a 36/46F dual drainage venous cannula (Terumo/Sarns, Ann Arbor, MI). A 24F Flexible Aortic Arch cannula (Terumo/Sarns) was used for aortic cannulation. In patients requiring a femoral approach for ECMO, 15 to 25F cannulae (Medtronic Cardiopulmonary) were used to create the venoarterial loop.

Patient management
After adequate hemostasis, patients on ECMO received heparin to keep activated clotting times between 180 and 200 seconds. Packed red blood cells were given to keep hematocrits at approximately 30. Platelets were given to keep platelet counts around 100,000. Fresh frozen plasma and cryoprecipitate were given as needed. Mean arterial blood pressures were maintained between 65 and 85 mm Hg. The minimally accepted blood flow rate was a cardiac index of 2.0 L/min/m². Blood flow rates were determined by preload and venous PO₂. Central venous pressures were maintained between 8 and 15 mm Hg, whereas venous PO₂ was kept between 30 and 45 mm Hg. The ventilator settings of the ECMO system were adjusted to maintain an arterial PO₂ between 150 and 300 mm Hg and an arterial PCO₂ between 35 and 45 mm Hg.

Weaning from ECMO
Generally, no attempt was made at weaning patients off ECMO until after 12 to 24 hours of support. When an attempt was made at weaning, transesophageal echocardiography was used to monitor heart function. Visual inspection of the heart was also performed if the patient’s chest was open. During weaning, ECMO flows were gradually reduced to 1 L/min/m². Inotropic agents were used to facilitate weaning in all patients. Patients who maintained adequate ventricular function with a cardiac index of at least 2 L/min/m² were decannulated; otherwise ECMO was reinstituted.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Survival
Extracorporeal membrane oxygenation was used in 51 adult postcardiotomy patients. Average preoperative ejection fraction for all patients placed on ECMO was 30.6% ± 0.55%. Average preoperative ejection fraction for the non–heart transplant group subset was 34.0% ± 0.65%. Weaning and survival statistics are presented in Table 1. No specific intraoperative complications that led to the use of postcardiotomy ECMO were identified. Of the patients placed on postcardiotomy ECMO, 16 (5 patients with heart transplants and 11 with other cardiac procedures, 31%) weaned and 8 (3 patients with heart transplants and 5 with other cardiac procedures, 16%) survived. Exclusion of the 18 patients who suffered prolonged cardiac arrest (> 5 minutes) before ECMO placement in an intensive care unit (ICU) yielded a survival rate of 24% (8 of 33). No patients requiring a significant period of cardiopulmonary resuscitation (> 5 minutes) survived.

Indications for ECMO
In the heart transplant group, 4 patients were placed on ECMO for pulmonary hypertension that was refractory to pharmacologic therapy that included inhaled nitric oxide. All of these patients had at least moderate pulmonary hypertension on preoperative pulmonary artery catheterization that was reversible. Three of these patients weaned and 2 survived long term. The other 3 patients in the heart transplant group were placed on ECMO for primary graft dysfunction resulting in cardiogenic shock. Two of these patients weaned and 1 survived long term. All patients in the non–heart transplant group were placed on ECMO for cardiogenic shock.

Negative weaning correlations
Univariate analysis of preoperative variables for the entire population revealed that patients aged more than 65 years were less likely to wean from ECMO compared with patients aged less than 65 years (15% vs 42%, respectively, p = 0.04; Fig 1) and were also less likely to survive (0% vs 26%, respectively, p = 0.01). Analysis of these same preoperative variables in the non–heart transplant group alone revealed patients aged more than 65 were less likely to survive after ECMO compared to patients aged less than 65 (0% vs 21%, p = 0.04). For the entire population in the postoperative period, patients with ejection fractions less than 30% after 2 days of ECMO were significantly less likely to wean (8% vs 54%, respectively, p < 0.001; Fig 2) and less likely to survive (4% vs 27%, respectively, p = 0.03) compared with patients with ejection fractions greater than 30%. Similarly, in the non–heart transplant group alone, patients with ejection fractions less than 30% after 2 days of ECMO were significantly less likely to wean (4% vs 53%, respectively, p < 0.001) and less likely to survive (0% vs 26%, respectively, p = 0.01) compared with patients with ejection fractions greater than 30%. For the entire population, no patients aged more than 75 years or with ejection fractions less than 20% after 48 hours of ECMO were able to wean. There were no significant differences in cross-clamp and CPB times between patients who weaned (cross-clamp time 57.6 ± 5.02 minutes, CPB 159.4 ± 10.3 minutes) and those who did not (cross-clamp time 73.6 ± 7.53, CPB 178.2 ± 12.9) or in those who survived (cross-clamp time 63.0 ± 4.1 minutes, CPB 178.2 ± 12.9) and those who did not (cross clamp: 71.4 ± 1.9 minutes, CPB: 174.4 ± 2.7 minutes) for the entire population. Similarly, there were no differences in these variables noted in the non–heart transplant population. There were also no significant differences in weaning or survival between those placed on ECMO in the operating room (OR) and those placed on ECMO in an ICU for both the entire population (OR: 9 of 22 weaned, 5 of 22 survived; ICU: 7 of 29 weaned, 3 of 29 survived) and the non–heart transplant group of patients (OR: 6 of 18 weaned, 3 of 18 survived; ICU: 5 of 26 weaned, 2 of 26 survived).

View larger version (24K): [in this window] [in a new window]   Fig 1. Percent survival based on age group.

View larger version (29K): [in this window] [in a new window]   Fig 2. Percent survival based on ejection fraction (%) by transesophageal echocardiogram after 48 hours of extracorporeal membrane oxygenation.

Length of time on ECMO
Length of time on ECMO was not significantly different between the heart transplant and non–heart transplant groups (85.0 ± 12.5 vs 64.7 ± 9.2, respectively, Table 2). However, time on ECMO was significantly longer in the heart transplant group patients who weaned (91.7 ± 2.7 hours) compared with the non–heart transplant group (47.4 ± 2.6, p = 0.008) patients who weaned. Similarly, time on ECMO was significantly longer in the heart transplant group survivors (101.3 ± 7.5 hours) compared with survivors in the non–heart transplant group (28.3 ± 11.9 hours, p < 0.001). In the heart transplant group, 2 patients survived after 96 hours of ECMO. One of these patients had severe pulmonary hypertension (113 hours of ECMO) and the other was placed on ECMO for primary graft failure (104 hours of ECMO). None of the non–heart transplant patients survived after 96 hours of ECMO and only 1 survived after 48 hours. The 1 survivor after 48 hours of ECMO received support for 56 hours. After weaning, this patient continued to have an extremely poor ejection fraction and was placed on the heart transplant waiting list before discharge.

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
Extracorporeal membrane oxygenation in postcardiotomy patients is most commonly used for support after failing to wean off of CPB and for delayed postcardiotomy cardiogenic shock. The significant complication rate related to ECMO restricts its use to patients who are in extremis or have continued shock despite maximal support [1–3]. In the current study, 0.9% of postcardiotomy patients were placed on ECMO with a subsequent survival rate of 16% for all patients. This survival rate increases to 24% (8 of 33) with the exclusion of patients requiring a prolonged period of CPR before ECMO. Magovern and Simpson [1], however, report a survival rate of 36% for all patients. Similarly, Muehrcke and colleagues [2] found a survival rate of 30% in their postcardiotomy patients on ECMO. The difference in survival rates between the current study and other investigations is likely related to the aggressiveness with which patients were placed on postcardiotomy ECMO. Only 0.4% of all cardiac surgery patients in the series of Muehrcke and colleagues [2] were placed on ECMO. Similarly, only 0.7% of patients in the study by Magovern and Simpson [1] received ECMO. The higher mortality rate in our series may represent a patient selection bias toward increased use of ECMO in moribund patients who have a severely decreased chance for recovery. In our series, there were no survivors in the group that required a significant period of CPR before placement on ECMO. The study by Magovern and Simpson [1] also showed no survival in those who required prolonged CPR before support.

Trying to determine the point at which ECMO becomes futile has not been well established in postcardiotomy patients. In the study by Magovern and Simpson [1], the mean length of ECMO support was shown to be 37.3 ± 12.7 hours for survivors in the non–heart transplant group. The two survivors in the heart transplant group from that study were on ECMO for 36 and 41 hours. We had similar results in our non–heart transplant group (mean ECMO time 28.3 ± 11.9 hours). In our series, however, a surprising finding was the length of time on ECMO in the heart transplant group survivors. Length of time on ECMO for survivors was significantly longer in the heart transplant group (101.3 ± 7.5 hours) compared with the non–heart transplant group (p < 0.001). The difference in ECMO time between these two groups of survivors is likely a result of the different pathophysiologic states that required postcardiotomy ECMO.

For the non–heart transplant group, the ejection fraction preoperatively was fairly low (average 34.0% ± 0.65%) and, for many patients, it was hoped that reperfusion of possible "stunned" myocardium would restore contractile function [4, 5]. This poor preoperative ejection fraction combined with the additional myocardial dysfunction as a result of cardiac surgery and cardiopulmonary bypass likely caused the cardiogenic shock seen in these patients. The length of time on ECMO that was required for potential recovery in this population is not well studied. Magovern and Simpson [1] reported a mean ECMO time of 37 ± 12.7 hours for survivors in the non–heart transplant group. In the present investigation, ECMO time for survivors in the non–heart transplant group was 28.3 ± 11.9 hours and only 1 patient survived after 48 hours of ECMO; that patient survived after 56 hours of ECMO. Based on these results and studies by others, non–heart transplant postcardiotomy patients should be given 48–72 hours to allow recovery of "stunned" myocardium [1, 2, 6, 7]. After this time, alternate methods of support such as implantable VADs should be considered in non–heart transplant patients who are potential transplant candidates and have not shown signs of myocardial recovery [5, 6, 13].

Patients on ECMO for support after heart transplantation fall into two groups. The first group comprises those with severe pulmonary hypertension. A small number of studies in the early heart transplant era have analyzed the time course for resolution of pulmonary hypertension postoperatively. Bhatia and colleagues [14] showed early on that a significant decrease in mean PAP pressures occurred 2 weeks after heart transplantation. In another study by Bourge and colleagues [15], a significant decrease in PVR occurred 1 week after transplantation. Despite these studies, pulmonary hypertension and subsequent right-sided heart failure continue to be a source of morbidity and mortality in the early postoperative period [16]. The time needed to allow for potential reversal of severe pulmonary hypertension is not known. In the present investigation, 4 of the 7 patients placed on ECMO after heart transplantation had severe pulmonary hypertension as the primary indication for ECMO. One of the 2 survivors in that group had severe pulmonary hypertension that did not reverse until after 96 hours of ECMO; that patient was on ECMO for 113 hours. This suggests that ECMO may be required for up to 5 days after heart transplantation to allow reversal of pulmonary hypertension.

The second indication for ECMO in patients with heart transplants is primary graft failure secondary to reperfusion injury [8, 9]. The degree of potential recovery from reperfusion injury and the time required to allow for recovery are not precisely known. Magovern and Simpson [1] reported 4 patients placed on ECMO for primary graft failure; the 2 survivors in that group were on ECMO for 36 and 41 hours. In our study, 3 of the 7 heart transplant patients required ECMO for primary graft failure; of the 2 patients who weaned in that group, 1 survived after 104 hours of ECMO support. Given these results, an extended period of ECMO support may be needed in heart transplant patients to allow recovery from reperfusion injury.

In summary, the decision to discontinue ECMO for postcardiotomy support should be predicated on the initial indication for its use and individual patient factors. Patients having non–heart transplant surgery should be given 48 to 72 hours of ECMO to allow recovery of potentially "stunned" myocardium. Recovery of additional heart muscle after this time period is unlikely, and implementation of an implantable VAD should be considered in patients who are transplant candidates. For patients who are not heart transplant candidates, withdrawal of support should be considered after 48 to 72 hours of ECMO, especially in those with ages greater than 75 years or ejection fractions less than 20% after 48 hours of ECMO. In contrast, both severe pulmonary hypertension and primary graft failure in heart transplant patients may take more than 4 days to improve. Given these recoverable mechanisms of severe pulmonary and cardiac dysfunction, up to 120 hours of ECMO support seems justified in heart transplant patients. Clearly, however, early withdrawal may occur in patients as a result of ECMO complications such as stroke or MSOF. Finally, ECMO is unlikely to benefit postcardiotomy patients requiring a significant period of CPR before support and should be avoided in this setting.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment References

 
This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/section/atsdiscussion/

	References

Top Footnotes Abstract Introduction Material and methods Results Comment References

 

1. Magovern G.J., Simpson K.A. Extracorporeal membrane oxygenation for adult postcardiotomy support. Ann Thorac Surg 1999;68:655-661.
2. Muehrcke D.D., McCarthy P.M., Stewart R.W., et al. Complications of extracorporeal life support systems using heparin bound surfaces. J Thorac Cardiovasc Surg 1995;110:843-851.
3. Kitamura M., Aomi Shigeyuki, Hachida M., et al. Current strategy of temporary circulatory support for severe cardiac failure after operation. Ann Thorac Surg 1999;68:662-665.
4. Pennington D.G., Joyce L.D., Pae W.E., Burkholder J.A. Circulatory Support Symposium of The Society of Thoracic Surgeons: patient selection. Ann Thorac Surg 1989;47:77-81.
5. Pennington D.G., Farrar D.J., Loisance D., et al. Circulatory Support Symposium of The Society of Thoracic Surgeons: patient selection. Ann Thorac Surg 1993;55:206-212.
6. Lazzara R.R., Magovern J.A., Benkart D.H., et al. Extracorporeal membrane oxygenation for adult postcardiotomy cardiogenic shock using a heparin bonded system. ASAIO J 1993;39:M444-M447.
7. Magovern G.J., Magovern J.A., Benkart D.H., et al. Extracorporeal membrane oxygenation: preliminary results in patients with postcardiotomy cardiogenic shock. Ann Thorac Surg 1994;57:1462-1471.
8. Pinsky D.J. The vascular biology of heart and lung preservation for heart and lung transplantation. Thromb Haemost 1995;74:58-65.
9. Young J.B., Naftel D.C., Bourge R.C., et al. Matching the heart donor and heart transplant recipient. Clues for successful expansion of the donor pool: a multivariable, multiinstitutional report. J Heart Lung Transplant 1994;13:353-365.
10. Lindelow B., Andersson B., Waagstein F., Bergh C.H. High and low pulmonary vascular resistance in heart transplant candidates. Eur Heart J 1999;20:148-156.
11. Auler J.O., Carmona M.J., Bocchi E.A., et al. Low doses of inhaled nitric oxide in heart transplant recipients. J Heart Lung Transplant 1995;15:443-450.
12. Espinoza C., Manito N., Roca J., et al. Reversibility of pulmonary hypertension in patients evaluated for orthotopic heart transplantation: importance in the postoperative morbidity and mortality. Transplant Proc 1999;31:2503-2504.
13. Pennington D.G., Hahn C.J. Circulatory support: discussion of experience with generally available devices. Ann Thorac Surg 1996;61:311-313.
14. Bhatia S.J.S., Kirshenbaum J.M., Shemin R.J., et al. Time course of resolution of pulmonary hypertension and right ventricular remodeling after orthotopic cardiac transplantation. Circulation 1987;76:819-826.
15. Bourge R.C., Kirklin J.K., Naftel D.C., et al. Analysis and predictors of pulmonary vascular resistance after cardiac transplantation. J Thorac Cardiovasc Surg 1991;101:432-445.
16. Chau E.M.C., Bailey K.R., Mahoney D.W., et al. Predictors of pulmonary hypertension in cardiac transplant recipients in the first postoperative year. Circulation 1996;94(Suppl II):II267-II272.

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This Article Abstract Full Text (PDF) Online Discussion Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Curtis G. Tribble John A. Kern Irving L. Kron Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fiser, S. M. Articles by Kron, I. L. Search for Related Content PubMed PubMed Citation Articles by Fiser, S. M. Articles by Kron, I. L. Related Collections Mechanical Circulatory Assistance