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Ann Thorac Surg 2004;77:151-157
© 2004 The Society of Thoracic Surgeons
a Department of Cardiac Surgery, Heart Center, University of Leipzig, Leipzig, Germany
Accepted for publication July 3, 2003.
* Address reprint requests to Dr Doll, Department of Cardiac Surgery, Heart Center, University of Leipzig, Strümpellstrasse 39, 04289 Leipzig, Germany.
e-mail: dolln{at}medizin.uni-leipzig.de
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Abstract |
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METHODS: During 5 years 219 of 18,150 patients (1.2%) undergoing cardiac surgery (coronary artery bypass grafting, n = 119; aortic valve replacement, n = 24; coronary artery bypass grafting and aortic valve replacement, n = 21; coronary artery bypass grafting and mitral valve replacement , n = 11; other procedures, n = 44) required temporary postoperative ECMO support. The ECMO implantation was performed through the femoral vessels or through the right atrium and ascending aorta. Additional intraaortic balloon counterpulsation was employed in 144 patients to improve coronary blood flow.
RESULTS: Mean duration of ECMO support was 2.8 ± 2.2 days. One hundred thirty-four patients (60%) were successfully weaned from ECMO. Of these, 52 patients (24%) were discharged from the hospital after 29.9 ± 24 days. The main cause of death was myocardial failure. Five-year follow-up is 96% complete; 37 patients (74%) were alive with reasonable exercise capacity.
CONCLUSIONS: Extracorporeal membrane oxygenation is an acceptable technique for short-term treatment of refractory postoperative low cardiac output. It can save the lives of a group of very high risk patients.
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Introduction |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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The first successful ECMO as a temporary assist device was used in 1972 when a motorcycle accident victim was managed with venoarterial extracorporeal support for 3 days [6]. The initial results of ECMO with adult respiratory distress syndrome showed poor outcome [7]. However several subsequent studies have reported the successful use of ECMO for temporary circulatory support in patients with cardiopulmonary failure [3, 8–10].
The purpose of this study was to evaluate the early and the 5-year outcome after short term ECMO support and to determine specific predictors of survival. We analyzed the results of an easily deployable ECMO circuit used in a large number of patients from a single institution.
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Material and methods |
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Patients were grouped as follows: group 1, ECMO after isolated coronary artery bypass grafting ([CABG] n = 119); group 2, ECMO after CABG and aortic valve replacement (n = 21); group 3, ECMO after isolated aortic valve replacement (n = 24); group 4, ECMO after CABG and mitral valve surgery (n = 11); and group 5, ECMO after other operations (n = 44). The last group ("other") included patients undergoing mitral valve operation (n = 9), pulmonary embolectomy (n = 6), repair of acute aortic dissection (n = 5), aortic aneurysm repair (n = 7), double valve replacement (n = 6), heart transplantation (n = 4), postinfarction ventricular septal defect closure (n = 3), tricuspid valve repair and pulmonary valve replacement (n = 2), pericardectomy (n = 1), and CABG with endoventricular resection of left ventricular aneurysm (n = 1).
Forty-one of those 219 patients (18.7%) received redo cardiac surgical interventions. Previous operations were as follows: CABG (n = 26), CABG plus aortic valve replacement (n = 2), aortic valve replacement (n = 5), mitral valve replacement (n = 1), CABG plus mitral valve replacement (n = 1), double valve replacement (n = 2), cardiac transplantation (n = 2), ascending aorta replacement (n = 1), and postinfarction ventricular septal defect closure (n = 1).
Extracorporeal membrane oxygenation circuit
The ECMO perfusion system consisted of a centrifugal pump (Vortex CN80; BioMedicus, Medtronic, Englewood, CA) and a pressure-controlled biocompatible heparin-coated polypropylene oxygenator (Affinity; Omnis AOT GmbH, Bad Oyenhausen, Germany [membrane surface area of 2.5 m2 and a maximum blood flow of 7.0 L/min]) and a heat exchanger.
The arterial return cannula (15F to 21F) was inserted directly into the ascending aorta (n = 159), into the femoral artery (n = 54), and into the subclavian artery (n = 6). Initially femoral cannulation was performed percutaneously and then through a 6-mm Hemashield prosthesis (Textile Development Associates, Inc, New York, NY) anastomosed to the femoral artery. Venous drainage was achieved with a 21F to 28F cannula inserted either directly into the right atrium (n = 133) or into the femoral vein with placement of the tip just proximal to the right atrium (n = 86). In addition 3 patients required cannulation of the left atrium to obtain better drainage of the heart. The ECMO flow was gradually increased to 4.5 L/min and adjusted as necessary to meet the hemodynamic and oxygen requirements of the patient. In some patients with renal insufficiency a hemofiltration unit was integrated into the circuit when required.
Management strategy
The ECMO blood flow was adjusted to achieve a mixed venous oxygen saturation (SvO2) of 70%; oxygen flow (FiO2) was titrated to maintain a postoxygenator partial oxygen pressure of 300 mm Hg or greater. Carbon dioxide was kept within the normal range (37 to 42 mm Hg).
During ECMO support intravenous heparin was administered continuously and titrated to achieve an activated clotting time (ACT) of 160 to 180 seconds. The oxygenator was monitored closely for the development of clots and was changed immediately if perfusion pressures started to increase. Platelets were administered to maintain a platelet count more than 150,000. Fresh frozen plasma, coagulation factors, and antithrombin III were administered as required.
Mechanical ventilation was continued throughout the arteriovenous ECMO with biphasic positive airway pressure. Ventilator settings were most commonly set at a tidal volume of 7 mL/kg, 8 breaths per minute, positive end expiratory pressure of 10 cm H20, a maximum ventilation pressure of 20 cm H20, and an FiO2 of 0.3.
Inotropic agents were reduced to a minimum to allow for optimal myocardial recovery while still maintaining left ventricular ejection. Norepinephrine was used to correct low peripheral vascular resistance and to maintain a mean arterial blood pressure of 70 to 75 mm Hg. Intraaortic balloon pump support was employed in 144 patients to decrease afterload, increase coronary perfusion, and increase pulsatility. We did not routinely vent the left ventricle.
Selected patients showing no sufficient recovery were converted to a long-term assist device. Other patients underwent heart transplantation after weaning from ECMO or after insertion of a permanent assist device.
Patients were weaned from ECMO as soon as possible; maximum anticipated support time was 4 to 5 days. Adequate systemic oxygen delivery was used as a signal of significant improvement of lung and cardiac function. While weaning the patient off ECMO the ACT was adjusted to 180 seconds when flow was reduced. Weaning was achieved over a period of several hours, with decannulation performed immediately thereafter. Cardiac function was continuously monitored with transesophageal echocardiography during the weaning process. Ventilator settings were increased to a rate of 12 breaths per minute, a positive end-expiratory pressure of 5 mbar, and an Fi02 of 0.5 with a peak inspiratory pressure of 25 mbar achieving a minimal tidal volume of 10 mL/kg.
After 5 years the patients discharged from the hospital were examined at our outpatient clinic to assess their clinical status, exercise capacity, and quality of life.
Statistical analysis
All statistical analyses were performed with the SAS system (SAS Institute, Cary, NC). Categorical variables are expressed as percentages and were evaluated with the 
2 or Fisher's exact test. Continuous variables are expressed as mean ± SD and were evaluated by Student's t or the Wilcoxon rank sum tests. Stepwise logistic regression analysis was used to determine the independent predictors of in-hospital mortality. Long-term survival was calculated according to the Kaplan-Meier method. Independent predictors of long-term survival were determined by Cox proportional hazards modeling. Statistical significance was considered at a p level of less than 0.05.
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Results |
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An intraaortic balloon pump was applied in 144 patients overall (66%), in 70% of the patients who were weaned form ECMO, in 59% of the patients who could not be weaned, in 73% of the long-term survivors, and in 63% of the nonsurvivors.
Of interest of all the 133 patients weaned from ECMO 93 (70%) had an intraaortic balloon pump; of the 86 patients who were unable to be weaned only 51 (59%) had an intraaortic balloon pump. Moreover 38 (73%) of the patients who were discharged from hospital had an intraaortic balloon whereas of the 167 patients who did not survive only 105 (63%) had an intraaortic balloon pump.
Eight patients were suitable for bridging to a long-term ventricular assist device. Of these patients 2 received the HeartMate System (Thoratec, Woburn, MA). Both of these patients had CABG as their original operation and both were successfully transplanted. The remaining 6 patients were bridged to a biventricular (n = 4) or univentricular (n = 2) Berlin Heart (Mediport Kardiotechnik, Berlin, Germany) assist device. In this group only 1 patient was successfully weaned, making the mortality rate 83% among the patients with the Berlin Heart assist device. Of the remaining 5 patients, 1 died of cerebral bleeding, 2 of cerebral infarction, and 2 of multiorgan failure.
The ECMO support was associated with significant morbidity in this high-risk patient group as shown in Table 4. Limb ischemia secondary to direct arterial cannulation (n = 16) did not occur any longer with graft interposition. Fasciotomy for severe leg ischemia was required in 13 (6%) of these patients. The rate of infection was 24%. Thirty-four patients (16%) suffered from a neurologic complication due to cerebral hemorrhage (n = 11), cerebral edema (n = 13), and cerebral infarction (n = 10). Renal failure occurred in 127 patients (58%) and 122 patients (56%) required hemofiltration. Significant mediastinal bleeding requiring rethoracotomy occurred in 136 patients (62%). The mean number of transfused red blood cell units for all the patients was 24.5 ± 21.0 units. Table 5 shows the major complications of all the five groups of patients. Comparing the five groups there was no statistical difference among the groups in terms of incidence of sepsis, neurologic, complications, bleeding requiring mediastinal exploration, and the amount of transfused red blood cells.
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Independent predictors of in-hospital survival were younger age, absence of preoperative myocardial infarction, absence of diabetes mellitus, use of intraaortic balloon, and operative procedures not defined as "other" prior to ECMO support. Independent predictors of survival at 5 years were younger age and absence of diabetes. Kaplan-Meier survival is illustrated in Figure 1. If the patients managed to survive the hospitalization and get discharged, their chance of survival within the next 5-year period was quite good.
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Our preference for further treatment of this critical group of patients has been the use of ECMO to provide ventricular and respiratory support. Several studies have demonstrated mortality rates of 50% to 70% among patients requiring ECMO support [1, 3, 8, 14–16]. Predictors of increased mortality were old age, evidence of organ system dysfunction, history of previous cardiac operation, extensive aortic operations, neurologic events, and not using an intraaortic balloon pump, as has been shown before [8].
For our patient group there was a substantial in-hospital (76%) and 5-year follow-up mortality rate (82%). However we were able to discharge 24% of these critically ill patients and 18% were well at follow-up. Of interest is that patients undergoing combined CABG and aortic valve replacement had a mortality rate of 95%, which was worse than that of the other surgical groups. The reason for the extremely poor outcomes is not clear but may be due to the deleterious combination of ventricular hypertrophy and myocardial ischemia.
Cannulation for ECMO support is now mostly performed on the ascending aorta and the right atrium maintaining the cardiopulmonary bypass cannulas. That is advantageous in order to avoid limb ischemia as seen with femoral canulations early in our series. The chest remains routinely open with sterile draping to prevent functional tamponade.
The use of an intraaortic balloon pump to maintain pulsatility during ECMO support is not uniformly agreed upon in the literature. However patients with intraaortic balloon pumps had a significantly higher survival rate. Thus we believe that intraaortic balloon pump counterpulsation is important during ECMO support to increase pulsatility, improve coronary perfusion, and decrease the ventricular afterload. Because the potential gains we recommend concomitant intraaortic balloon pumps for all patients on ECMO support.
Bleeding continues to be a major complication of ECMO support [11, 17–19]. Heparin-coated circuits or the use of lower doses of heparin or antifibrinolytic agents such as aminocaproic acid and aprotinin have been recommended but their use has had mixed results [2, 20, 21]. As a moderate amount of anticoagulation will always be required we think that less traumatic pumps with improved hydrodynamics and silicone membrane oxygenator may decrease mechanical stress and damage to blood components to further reduce these complications.
Other issues of management include precise monitoring and adjustment of gas exchange during ECMO support. Allowing some lung perfusion during ECMO may prevent reperfusion pulmonary edema. Therefore subtle adjustments of CO2 over a period of at least 24 hours can prevent reactive cerebral hyperemia and the subsequent risk of cerebral hemorrhage during anticoagulation [22, 23] and enable some pulmonary perfusion. Mechanical ventilation with an FiO2 of less than 0.5 is recommended and low tidal volumes and positive end-expiratory pressure of 5 to 8 mm Hg should be employed to prevent alveolar collapse [24]. To prevent barotrauma peak ventilation pressures should not exceed 30 mm Hg. Nitric oxide should be used in the ventilation circuit when there is evidence of right ventricular dysfunction [25].
The weaning process of these patients can be very difficult, slow, and challenging [3]. In several series ECMO weaning protocols involve rapid reduction of flow from 2 L · min-1 · m-2 to zero in only a few minutes while ventricular function is observed through an open thorax or under transesophageal echocardiography control [15, 26]. In our patient cohort we found that slow weaning is advantageous. In some patients we had to increase the ECMO flow again after a rapid weaning period owing to a decreased mixed venous oxygen saturation (SvO2). After increasing the flow and a stepwise reduction over a longer time period, weaning from ECMO was possible. We recommend decreasing ECMO flows slowly down to 1 L/min over a 24- to 36-hour period regardless of the body surface area. That will allow the recovering myocardium to slowly adapt to the increasing demands [27]. Throughout the weaning process myocardial contractility is continuously monitored with transesophageal echocardiography. Owing to the heparin-coated polypropylene oxygenator and the heparin coated hoses an anticoagulation management with an ACT of 180 seconds is sufficient. Using this strategy we were able to successfully wean 133 patients (61%) from ECMO. This number is in the higher range of previously reported studies [3, 8–10, 14, 26].
After having weaned the patient from ECMO and after removing the cannulas, we connected the arterial to the venous hose and maintained a flow of patient's blood in the whole ECMO system for at least 2 hours. If the patient showed hemodynamic instability we had to recannulate the patient again. The next step for this patient is the implantation of a long-term assist device or a heart transplantation, on condition that no irreversible organ damage occurred.
The patients in this study managed to be successfully stabilized hemodynamically on ECMO and allowed time for their myocardium to recover. The ECMO support also provided time for some patients to be assessed for either transplantation or bridging to other assist devices. A total of 4 patients were able to have heart transplantation performed and all survived. Eight patients were bridged to left ventricular assist devices (6 to the Berlin Heart and 2 to the Heartmate device) and 3 survived. All the patients who survived transplantation or bridging to other devices are alive and doing well at 5 years. However a considerable number of the patients (n = 133) who were initially weaned from ECMO died in the following days. The primary cause of death was myocardial failure with no further options for reinterventions.
In conclusion management of ECMO requires a multidisciplinary approach and a significant amount of work, planning, and organization. We believe that venoarterial ECMO is a versatile method of supporting patients with postcardiotomy cardiogenic shock who otherwise would die. Extracorporeal membrane oxygenation can be used for temporary, complete circulatory support while awaiting myocardial recovery or determining suitability for heart transplantation. This study reports the outcome of the use of ECMO for postcardiotomy cardiogenic shock after initial hospital admission and after a 5-year follow-up period. During the hospitalization 61% of the ECMO patients were weaned successfully and 24% were able to be discharged from hospital. The variables predicting in-hospital survival after ECMO were younger age, absence of preoperative myocardial infarction, absence of diabetes, use of intraaortic balloon pump, and if the procedures performed prior to ECMO were valve, CABG, or valve/CABG (that is, not "other"). At the 5-year follow-up, 74% of the discharged patients were alive and having a satisfactory quality of life (New York Heart Association II). These patients have a low hospital readmission rate and their survival rate is stable over the 5-year period. Although postcardiotomy ECMO is associated with significant morbidity and mortality we believe that with proper organization and implementation, ECMO is a justifiable alternative treatment of patients who fail to be weaned from cardiopulmonary bypass after cardiac surgical operations. [28, 29]
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