Extracorporeal circulation is used therapeutically during renal dialysis, c
ardiopulmonary bypass (CPB), and extracorporeal membrane oxygenation (ECMO)
. All of these procedures result in activation of the body's natural defens
e mechanisms against "nonself" and foreign invasion. The prolonged duration
of ECMO compared with other applications and the absence of hypothermia, h
emodilution, ischemia/reperfusion, and protamine administration make the ho
st response to ECMO subtly distinct. In this review, the host response to E
CMO is discussed and contrasted to CPB. The use of aprotinin and other resp
onse modifiers is also considered.