Plasma epinephrine levels in resuscitation with cardiopulmonary bypass. Since the highest plasma epinephrine levels have been recorded during resuscitation, we evaluated the isolated effect of cardiac arrest upon adrenomedullary secretion. We determined plasma epinephrine in dogs resuscitated with cardiopulmonary bypass (CPB) after cardiac arrest periods of 12 (CPB-12; n = 4) or 16 min (CPB-16; n = 5). Through 2 h of CPB and the following 6 h of critical care, there was no difference between CPB-12 and CPB-16 regarding most cardiopulmonary functional variables. Plasma epinephrine was markedly elevated immediately after initiation of CPB (p less than .01 at 1 min CPB vs. basal) and returned rapidly to basal concentrations. Comparison of plasma epinephrine levels between CPB and standard CPR groups showed that responses to cardiac arrest were similar (p greater than .05 at 1 min CPB vs. 11.5 min CPR). We conclude that cardiac arrest is the main or sole determinant of the plasma epinephrine elevation of resuscitation. 