Over the past two decades, veno-venous extracorporeal membrane oxygenation (VV-ECMO) has progressed rapidly in technology, ease of application, and safety. It is now frequently employed in the support of patients with severe acute respiratory failure.1 Factors routinely considered in the evaluation of a patient’s candidacy for VV-ECMO cannulation include age, pre-existing lung disease and nonpulmonary comorbidities, associated organ system involvement, and the perceived reversibility of the acute respiratory failure. Cardiac arrest before VV-ECMO cannulation has historically been associated with increased mortality.3 Acuity of presentation often precludes reliable determination of a postarrest neurologic examination in these patients, making prognosis before cannulation difficult. Of multiple scoring systems for risk stratification, only the Respiratory ECMO Survival Prediction (RESP) score considers cardiac arrest as a factor.3–7 Two large randomized trials of standard ventilation versus VV-ECMO support for acute respiratory failure have been performed in the modern ECMO era, neither of which looked at a postcardiac arrest cohort.2,8 Bhardwaj et al.9 recently reported 57% mortality in a case series of 21 patients cannulated for VV-ECMO after cardiac arrest, but without a noncardiac arrest cohort for comparison. The purpose of our study was to evaluate outcomes in patients cannulated for VV-ECMO when stratified by those who did and did not sustain a cardiac arrest before cannulation.
Approval was obtained from the University of Maryland School of Medicine institutional review board. Patients admitted to the Lung Rescue Unit (LRU) for VV-ECMO support between 2014 and 2018 were retrospectively reviewed. Trauma patients and lung transplant patients were excluded. Patients were stratified into cardiac arrest and noncardiac arrest groups. Demographics, PaO2/FiO2 ratio, Sequential Organ Failure Assessment (SOFA) score,10 and RESP score3 before cannulation were calculated.
For the cardiac arrest group, best Glasgow Coma Score (GCS) between arrest and cannulation, and best GCS before discharge for survivors, were calculated. All neuroimaging was reviewed. Duration of cardiac arrest was noted. In some instances, it was necessary to abstract time of arrest from non-numeric data, that is, “three rounds of cardiopulmonary resuscitation” was imputed to be three 2-minute rounds of compressions, for a total of 6 minutes of arrest time.
Our primary outcome was survival to hospital discharge. Secondary outcomes included number of days on VV-ECMO support, hospital length of stay, neurologic status at time of discharge, ventilator dependence at time of discharge, and discharge status (home vs. rehabilitation or inpatient unit). Statistical analyses were performed using Stata Version 14 (StataCorp, College Station, TX). Categorical variables were compared using Fisher’s Exact Test. Continuous variables uniformly failed the Shapiro-Wilk test for normality and are reported as median (interquartile range). Medians were compared using the Wilcoxon rank-sum test. A P value of <0.05 was considered statistically significant, and all tests were two-tailed.
During the study period, 217 patients were cannulated for VV-ECMO and admitted to the LRU, 159 of whom met inclusion criteria. Twenty-eight patients (17.7%) sustained cardiac arrest before cannulation. There were no differences in median age, admission SOFA score, or pre-ECMO PaO2/FiO2 ratios between cardiac arrest and noncardiac arrest groups (Table 1). There was no significant difference in survival to discharge between cardiac arrest and noncardiac arrest groups (71% vs. 76%, P = 0.37). Adjusting for the effect of cardiac arrest on the RESP score, there was no difference in precannulation RESP scores between the two groups (3 (0–6) vs. 4 (2–5); P = 0.72; Table 1).
For patients with pre-ECMO cannulation cardiac arrest, there was no difference in median age, body mass index, precannulation PaO2/FiO2 ratio, admission RESP score, admission SOFA score, or days intubated before cannulation between survivors and nonsurvivors (Table 2). Survivors after cardiac arrest had a shorter median arrest time. No survivors had cardiac arrest for greater than 13 minutes.
Of the 28 patients in the cardiac arrest group, six had a postarrest GCS greater than 3 before cannulation. All six patients survived to discharge. Of the remaining 22 patients with postcardiac arrest GCS of 3 before cannulation, 14 (63.6%) survived to hospital discharge. Of the eight patients who died, five were caused by anoxic brain injury; three were caused by multisystem organ failure. Of the 20 postarrest patients who survived to discharge, all were neurologically intact. Five were discharged home and 15 to a rehabilitation facility. Seven patients who had sustained cardiac arrest underwent a noncontrast head computed tomography (CT) scan before cannulation. All CT scans were read as normal without acute abnormalities. Five of these patients, all with GCS of 3 before cannulation died.
A number of precannulation risk stratification scores have been developed in an attempt to predict outcomes for patients considered for initiation of VV-ECMO.3–7 Only the RESP score, derived from a retrospective logistic regression of 2355 patients, includes antecedent cardiac arrest as a negative predictive factor with an odds ratio (95% confidence interval) of 0.62 (0.45–0.85), P = 0.003.3 Cardiac arrest before cannulation was not evaluated as a factor in the Predicting Death for Severe ARDS on VV-ECMO score, the Prediction of Survival on ECMO Therapy score, the ROCH score, or the ECMOnet score.4–7 Mortality at our institution after the development of the LRU has consistently been less than 30%.9 This is primarily attributed to the implementation of a multidisciplinary critical care team dedicated to the care of ECMO patients. Patient selection (survival to transfer from referring institutions) likely contributes to this lower mortality rate as well.
We have demonstrated that cardiac arrest before VV-ECMO cannulation is not an independent predictor of death before hospital discharge. Additionally, postarrest, precannulation neurologic status was not predictive of outcome, as all survivors to hospital discharge had complete neurologic recovery. Precannulation head CT, when performed, failed to predict outcome, as 71% of patients with normal imaging did not survive to hospital discharge. A principal limitation of our study is that it included only patients who were cannulated for VV-ECMO. It is possible that some patients had cardiac arrest and were not offered VV-ECMO because of poor neurologic prognosis and were not included.
Providing VV-ECMO support to patients after cardiac arrest with return of spontaneous circulation can be associated with survival to discharge rates similar to those with acute respiratory failure who have never sustained cardiac arrest. Occurrence of cardiac arrest alone should not preclude the application of VV-ECMO. Additionally, obtaining CT imaging for neurologic prognosis in the postarrest patient before cannulation does not appear to meaningfully predict outcomes and should not delay initiation of VV-ECMO in this patient cohort.
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