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J Thorac Cardiovasc Surg 2008;135:382-388
© 2008 The American Association for Thoracic Surgery

Cardiopulmonary Support and Physiology

Venoarterial extracorporeal membrane oxygenation for treatment of cardiogenic shock: Clinical experiences in 45 adult patients

^a Department of Thoracic and Cardiovascular Surgery, Johann Wolfgang Goethe University Hospital, Frankfurt/Main, Germany
^b Department of Perfusion and Cardio-technique, Johann Wolfgang Goethe University Hospital, Frankfurt/Main, Germany
^c Department of Anaesthesiology, Intensive Care Medicine, and Pain Therapy, Johann Wolfgang Goethe University Hospital, Frankfurt/Main, Germany
^d Department of Biomedical Statistics, Johann Wolfgang Goethe University Hospital, Frankfurt/Main, Germany.

Received for publication January 31, 2007; revisions received May 13, 2007; accepted for publication August 9, 2007.

^_* Address for reprints: Farhad Bakhtiary, MD, Department of Thoracic and Cardiovascular Surgery, Johann Wolfgang Goethe University, Theodor Stern Kai 7, 60590 Frankfurt am Main, Germany (Email: farhad{at}bakhtiary.de).

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
Objective: Venoarterial extracorporeal membrane oxygenation is an established treatment option in patients with cardiogenic shock. This report reviews our 3-year experience with this support system with respect to early and midterm outcome, as well as predictors of survival.

Methods: From January 2003 until November 2006, 45 (0.8%) of 5750 patients undergoing cardiac surgery procedures required the following: temporary extracorporeal membrane oxygenation support coronary artery bypass grafting, n = 20; implantation of a left ventricular assist device, n = 5; heart transplantation, n = 1; heart and lung transplantation, n = 1; coronary artery bypass grafting plus repair of postinfarction ventricular septal defect, n = 3; coronary artery bypass grafting plus mitral valve repair, n = 5; aortic valve replacement, n = 2; coronary artery bypass grafting plus aortic valve replacement, n = 3; and other procedures, n = 5. Extracorporeal membrane oxygenation implantation was performed through the femoral vessels or axillary artery or through the right atrium and ascending aorta. Additional intra-aortic balloon pumps were used in 30 patients.

Results: Average patient age was 60.1 ± 13.6 years. There were 35 male patients. Average duration of extracorporeal membrane oxygenation was 6.4 ± 4.5 days. Twenty-five patients could be successfully weaned from extracorporeal membrane oxygenation. The 30-day mortality was 53% (24/45 patients). The in-hospital mortality was 71% (32/45 patients). Thirteen (29%) patients could be successfully discharged. After a follow-up period of up to 3 years, 10 (22%) patients were still alive.

Conclusions: Extracorporeal membrane oxygenation offers sufficient cardiopulmonary support in adults with similar hospital and midterm survival rates to those of other mechanical support systems. Early indication, alternative peripheral cannulation techniques, and reduced anticoagulation to avoid perioperative bleeding could improve our results with increasing experience.

	Introduction

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Since the first implantation by Hill and colleagues,¹ extracorporeal membrane oxygenation (ECMO) has been an established treatment option in adult patients with refractory cardiogenic shock,² providing prolonged but temporary cardiac and respiratory support. Refractory myocardial dysfunction before or during cardiac surgical procedures with development of severe cardiogenic shock is a rare but serious complication accompanied by an almost 100% mortality. In this small group of patients, ECMO might provide sufficient hemodynamic support to allow recovery from reversible myocardial injury.^3,4

Many studies have reported excellent results of ECMO in children,⁵ with outcome depending on the indication for ECMO. In adults, ECMO was reported to be less successful, but early use demonstrated favorable results compared with secondary implantation.^6,7 Since 2002, we have used ECMO in our institution for patients who otherwise could not be weaned from extracorporeal circulation. The purpose of this study was to retrospectively review the early and midterm outcome of our patients and determine specific predictors of survival.

	Materials and Methods

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From January 2003 through November 2006, 45 of 5750 patients with refractory cardiogenic shock were placed on venoarterial ECMO by using heparin-coated circuits (Medtronic, Minneapolis, Minn). The criterion to use ECMO for cardiopulmonary support was the inability to treat cardiogenic shock with conventional methods of support, such as catecholamines or an intra-aortic balloon pump (IABP). The following cardiac surgical procedures were performed: coronary artery bypass grafting (CABG) for acute myocardial infarction and preoperative cardiogenic shock, n = 20; implantation of a left ventricular assist device, n = 5; heart transplantation, n = 1, heart and lung transplantation, n = 1; CABG plus repair of postinfarction ventricular septal defect, n = 3; CABG plus mitral valve repair, n = 5; aortic valve replacement (AVR), n = 2; CABG plus AVR, n = 3; and other procedures, n = 5.

ECMO Circuit
The ECMO circuit consisted of a closed, heparin surface-coated circuit of polyvinyl chloride tubing (Medtronic) and either a Biomedicus Biopump (Medtronic) or a Jostra-Maquet Rotaflow RF 32 (Jostra Medizintechnik, Hirrlingen, Germany), a centrifugal pump that propels blood through a hollow-fiber membrane oxygenator (Maxima P.R.F., Medtronic). Blood flow was monitored by using a Doppler flow probe placed on the arterial side of the circuit. Venoarterial ECMO was instituted by means of peripheral cannulation (common femoral artery and vein) in 29 (64%) patients, subclavian artery and femoral vein cannulation in 8 (18%) patients, and central cannulation (ascending aorta and right atrium) in 8 (18%) patients. Central cannulation was performed in patients, mainly in the early course of our experience. For better patient mobilization and avoidance of bleeding, possible thrombus formation at the arterial cannula, and infective complications in the presence of an open sternotomy we changed our strategy and switched to a femoral or subclavian cannulation. In 2 patients (1 receiving CABG and 1 receiving CABG plus mitral valve repair), retrograde femoral artery cannulation was converted to subclavian artery cannulation to achieve adequate ECMO support in regard to performing better upper body oxygen saturation.

To avoid limb ischemia observed in some early cases with peripheral cannulation, we optimized the distal limb perfusion by using an 8-mm Dacron T-graft (end-to-side anastomosis to the femoral or subclavian artery), which was tied on a 20F arterial cannula (Medtronic) to ascertain both central arterial blood flow and distal limb perfusion.

Initially, patients were heparinized as early as possible to achieve an activated clotting time of 160 to 180 seconds, but because we observed too many cases of diffuse bleeding complications, we began to antagonize heparin completely and maintain sufficient hemostasis to prevent further bleeding complications. Anticoagulation with heparin was started after chest drainage was less than 50 mL/h. The target partial thromboplastin time was between 50 and 60 seconds.

Multidisciplinary Management Strategy
All but 2 patients were supported with the intention to wean from ECMO (bridge to recovery). Intravenous inotropic doses were minimized or withdrawn to decrease myocardial oxygen demand and facilitate myocardial recovery, especially in patients with acute myocardial infarctions. IABP support was encouraged while patients received ECMO and was used in 30 of 45 patients. Atrial septostomy or ventricular venting was not used. Recovery was assessed daily by means of clinical, hemodynamic, and echocardiographic findings.

When recovery was unlikely, patients were evaluated for transplantation or permanent assist implantation. Candidacy for transplantation or left ventricular assist device implantation was made on a case-by-case basis. In all patients demonstrating recovery, weaning was performed, with slow reduction of ECMO flow over 48 hours. ECMO had to be withdrawn from some patients, with the knowledge that survival was unlikely and continued support was futile.

Pump flows were chosen to supply at least adequate total systemic circulatory support (2.5 L · min^–1 · m^–2) and to achieve a mixed venous oxygen saturation of more than 70%. Oxygen flow was gradually adjusted as necessary to meet the oxygen requirements of the patient. Pulmonary artery pressure and cardiac output were continuously monitored with a Swan–Ganz Catheter. Transesophageal echocardiography was performed multiple times in all patients while receiving ECMO to enable progressive assessment of myocardial recovery and provide useful information regarding myocardial contractility and ventricular filling during the weaning process.

General Patient Care
In all patients, sedation was morphine and midazolam based and was used to achieve patient comfort while enabling a daily neurologic assessment. Mechanical ventilation with biphasic positive airway pressure was continued throughout the ECMO period. ECMO was set at a tidal volume of 5 to 7 mL/kg, a rate of 8 breaths/min, a positive end-expiratory pressure of 10 cm H₂O to prevent alveolar collapse, and a maximum ventilation pressure of 20 cm H₂O to avoid barotrauma. PCO ₂ was kept within the normal range to prevent organ damage. Respirator settings were kept at parameters known to avoid additional lung injury to avoid development of pulmonary failure. Prone positioning was also used. ECMO flow was never reduced to less than 1 L/min until explantation to avoid any intrasystemic clotting. Enteral feeding was instituted in all patients on the first postoperative day and continued if tolerated.⁸ Antibiotics were used if infection was clinically suspected. Hyperglycemia was avoided by means of continuous infusion of insulin. Perfusion of the lower limbs was checked every 6 hours by means of physical examination, and 12-hour creatine kinase measurements were taken. All surviving patients were followed up after hospital discharge every 6 months in our outpatient department or by telephone to assess their clinical status and exercise capacity (100% complete follow-up).

Data Collection
Data collection was performed prospectively and focused on intraoperative and postoperative data, cannulation methods, duration of support, blood product use, use of hemofiltration, and use of IABP. Data were also obtained for 30-day mortality and in-hospital outcome.

Statistical Analysis
All statistical analyses were performed with the Statview program (Cary, NC). Categorical variables are expressed as percentages and were evaluated with ² or Fisher exact tests. Continuous variables are expressed as means ± standard deviation and were evaluated by using the Student t test or the Kruskal–Wallis test. Logistic regression analysis was used to determine the predictors of survival. Long-term survival was calculated according to the Kaplan-Meier method.

	Results

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Demographics and pre-ECMO risk profiles of the 45 patients are summarized in Table 1. The patients were divided into subgroups with relation to their indication for cardiac surgery.

In our early cases with ECMO, we observed a high incidence of bleeding complications. Therefore, we have changed our anticoagulation regimen. Systemic heparinization was not initiated until chest drainage reduced to less than 50 mL/h. The target partial thromboplastin time to be attained was between 50 and 60 seconds.

Limb ischemia was observed in 3 of the early patients in whom direct peripheral cannulation had been performed. As a consequence, distal limb perfusion was optimized with an 8-mm Dacron T-graft anastomosed end-to-side to the common femoral or subclavian artery to maintain both central arterial blood flow and distal limb perfusion.⁹ Fasciotomy of the lower leg was required in 6 patients because of compartment syndrome. The rate of systemic infection defined as a positive blood culture was 58% (26/45). Four (8.9%) patients had neurologic complications caused by cerebral hemorrhage (n = 3) and stroke (n = 1). Renal failure was the most common complication and occurred in 39 (86.7%) patients. All patients with renal failure required continuous venovenous hemofiltration. Rethoracotomy for bleeding or tamponade had to be performed in 39 (86.7%) patients. Table 4 lists the overall complications of ECMO support. There was no significant difference between the groups with different indications with regard to incidence of sepsis, neurologic complications, blood transfusions, rethoracotomy, or renal failure.

Twenty-five patients could be successfully weaned from ECMO, but only 13 patients could be discharged from the hospital. Therefore 12 of 25 patients had late complications with muliorgan failure and subsequently died.

The main causes of mortality in patients after successful weaning from ECMO were pulmonary infections and sepsis with consecutive multiorgan failure. These complications occurred more frequently in patients with advanced age and comorbidities, such as pulmonary hypertension and diabetes.

Independent predictors of hospital survival revealed in univariate regression analysis were absence of pulmonary hypertension (P = .04), absence of diabetes (P = .011), and use of IABP (P = .04).

Regarding underlying disease states, the best prognosis was observed for patients who were planned for permanent assist device implantation or transplantation (60%, Table 6).

View larger version (10K): [in this window] [in a new window]   Figure 1. Kaplan–Meier survival curve of all patients with extracorporeal membrane oxygenation and the number of patients at risk.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

In this patient group ECMO might provide sufficient hemodynamic and respiratory support to allow recovery from myocardial injury and extend the decision time for a bridging therapy. Recent studies report in-hospital survival rates with the use of ECMO ranging from 20% to 50% and mortality rates of 50% to 70%.^12,13 In our study there was a high 30-day mortality of 53%; in-hospital mortality was 71%, and 3-year mortality was 78%. Our survival rate is comparable with those of other study groups.^3,14

Based on the experience in our institution, ECMO therapy is now considered to be a valuable option for treatment of myocardial infarction and low output syndrome in cardiac procedures in the operating room. We postulate that patients with severe left ventricular dysfunction, severe cardiomyopathy, primary perioperative respiratory failure, postcardiotomy syndrome, and myocardial infarction might benefit more if they receive this treatment option during the operation or at least very early in the postoperative course to prevent clinical deterioration. Early use of circulatory support might avoid additional myocardial damage caused by inotropic medication or hypoxia and thus provides a treatment option that allows for recovery from the myocardial injury over a prolonged period. Patients in perioperative shock or those after long cardiac procedures need a high normal cardiac output to recover. On the other hand, patients who use a bridge to permanent assist device implantation or transplantation demonstrate the best outcome.

The use of IABP also was a predictor for better survival. Based on the hypothesis of additional pulsatile flow, reduction of afterload, and better coronary flow, we now use IABP routinely in patients undergoing ECMO who do not demonstrate contraindications to IABP.^13,14

In the early cases of ECMO, we observed frequent bleeding problems, especially when platelet inhibitors had been administered before surgical intervention. After changing our postoperative anticoagulation protocol, there was a reduction in bleeding complications, but still, most patients had to undergo reoperation at some point during the postoperative course.

Renal failure and need for hemofiltration was another frequent complication in our study group. Of interest is the high incidence of renal failure during the postoperative course of 9 patients, which occurred days after successful weaning from ECMO. Perioperative high lactate concentrations were observed in nonsurvivor patients; however, this did not reach statistical significance.

The duration of ECMO in our patient group was 6.4 ± 4.5 days and thus longer compared with those seen in other study groups.^3,13,14 Our strategy was to provide sufficient time to recover from myocardial injury; however, the study does not prove any benefit from that difference in strategy. The treatment duration should be decided individually, depending on heart and lung recovery. Improvement of our ECMO strategy to reduce system-related complications led us to extend the duration of ECMO to achieve maximal recovery.

The follow-up period was short but demonstrated that once successfully discharged from the hospital, patients had an acceptable midterm survival with class II to III heart failure and a low rate of readmission to the hospital. These results justify the use of ECMO, even if only slightly more than 20% of the patients survived up to 3 years after the cardiac operation.

In summary, current use of the heparin-precoated system and improvements in patient management reduced the complexity of ECMO. System-related complications are rare, and thus the threshold and timing for system implantation should be liberal. Therefore complex patients who currently might not be considered for ECMO could be able to benefit from ECMO in the future.

This article describes a retrospective analysis of our clinical experience with mixed indications for ECMO implantation. Despite a variety of changes in the management of our patients, we still had a relatively high rate of mortality.

	References

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