ABSTRACT
BACKGROUND: Even a small change in the pressure gradient between the venous system and the right atrium can have significant hemodynamic effects. Mean systemic filling pressure (MSFP) is the driving force of the venous system. As a result, MSFP has a significant effect on cardiac output. We aimed to test the hypothesis that the hemodynamic instability during induction of general anesthesia by intravenous propofol administration is caused by changes in MSFP. METHODS: We prospectively collected data from 15 patients undergoing major surgery requiring invasive hemodynamic monitoring. Hemodynamic parameters, including MSFP, were measured before and after propofol administration and following intubation, using venous return curves at a no-flow state induced by a pneumatic tourniquet. RESULTS: A significant decrease in MSFP was observed in all study patients after propofol administration (median (IQR) pressure 17 (9) mmHg compared with 25 (7) before propofol administration, p = 0.001). The pressure gradient for venous return (MSFP - central venous pressure; CVP) also decreased following propofol administration from 19 (8) to 12 (6) mmHg, p = 0.001. Central venous pressure did not change. CONCLUSIONS: These results support the hypothesis that induction of anesthesia with propofol causes a marked reduction in MSFP. A possible mechanism of propofol-induced hypotension is reduction in preload due to a decrease in the venous vasomotor tone.
