INFLUENCE OF ARTERIAL CARBON-DIOXIDE TENSION ON SYSTEMIC VASCULAR-RESISTANCE IN PATIENTS UNDERGOING CARDIOPULMONARY BYPASS

Background: The effects of induced hypothermia in cardiac surgical pat ients are not yet fully understood. Despite numerous studies on the ef fects of acid-base management on organ blood now, only little informat ion is available on the effects of alpha-stat versus pH-stat managemen t on systemic haemodynamics. We therefore compared the effect of alpha -stat and pH-stat acid-base management on systemic haemodynamics in a prospective, controlled, cross-over study. Methods: Twenty patients un dergoing coronary artery bypass surgery were included in the study. Ca rdiac output was measured by thermodilution. Cardiac index and systemi c vascular resistance were calculated according to standard formulae. Measurements were performed under hypo-and hypercapnia after induction of anaesthesia. Measurements were repeated at the end of two 30-min p eriods of pH-stat and alpha-stat acid-base management, respectively. R esults: Systemic vascular resistance at the lower PaCO2-levels (hypoca pnia and alpha-stat, respectively) was significantly higher than those at the higher level (hypercania and pH-stat, respectively). The perio ds of different PaCO2-levels were comparable with respect to haematocr it, blood viscosity and temperature. Systemic vascular resistance was not significantly different from the control period. Conclusions: This study demonstrates that during hypothermic cardiopulmonary bypass, sy stemic vascular resistance under alpha-stat acid-base management is hi gher than under pH-stat management. As obvious from measurements durin g the control period, this finding can be completely explained by the difference in PaCO2. (C) Acta Anaesthesiologica Scandinavica 42 (1998) .