Hemodynamic and hormonal responses to hypothermic and normothermic cardiopulmonary bypass

Abstract

Normothermic cardiopulmonary bypass (CPS) is used in cardiac surgery at some institutions. To compare hemodynamic and hormonal responses to hypothermic (29°C) and normothermic nonpulsatile CPS, 20 adults undergoing coronary artery bypass graft and/or aortic valve replacement were studied. Hemodynamic measurements and plasma hormone concentrations were obtained from preinduction to the third postoperative hour. The two groups were given similar amounts of anesthetics and vasodilators. Systemic vascular resistance increased only during hypothermic CPS, and heart rate was higher at the end of hypothermic CPS. Postoperative central venous pressure and pulmonary capillary wedge pressure were lower after hypothermic CPS. Oxygen consumption decreased by 45% during hypothermic CPS, did not change during normothermic CPS, but increased similarly in the two groups after surgery; mixed venous oxygen saturation (SvO 2) was significantly lower during normothermic CPB. Urine output and composition were similar in the two groups. In both groups, plasma epinephrine, norepinephrine, renin activity, and arginine vasopressin concentrations increased during and after CPS. However, epinephrine, norepinephrine, and dopamine were 200%, 202%, and 165% higher during normothermic CPS than during hypothermic CPB, respectively. Dopamine and prolactin increased significantly during normothermic but not hypothermic CPS. Atrial natriuretic peptide increased at the end of CPS and total thyroxine decreased during and after CPS, with no difference between groups. This study suggests that higher systemic vascular resistance during hypothermic CPS is not caused by hormonal changes, but might be caused by other factors such as greater blood viscosity. A higher perfusion index during normothermic CPS might have allowed higher SVO 2.