Mean systemic filling pressure indicates fluid responsiveness and anesthesia-induced "unstressed" blood volume

Abstract

Background. The mean systemic filling pressure (Pms) play a central role for the understanding of the circulation. We studied whether the Pms indicates fluid responsiveness before and after induction of general anesthesia and whether the Pms response to bolus infusions of fluid indicates an anesthesia-induced increase of the "unstressed" blood volume. Methods. An analog to Pms based on cardiac output, the mean arterial pressure, and central venous pressure (Pmsa) was calculated in 86 patients before induction of general anesthesia and before each of 3 successive bolus infusions of 3 ml/kg of colloid fluid. An increase in stroke volume of ≥ 10% from a bolus infusion indicated fluid responsiveness. Changes in blood volume were estimated from anthropometric data and the hemodilution. Results. Pmsa was lower in fluid responders than in non-responders before induction (13.2 ± 2.2 vs. 14.7 ± 2.7 mmHg; mean ± SD, P< 0.01) and after induction of general anesthesia (11.4 ± 2.1 vs. 12.8 ± 2.1 mmHg; P< 0.006). Changes in Pmsa resulting from the infusions did not differ depending on the stroke volume response. Receiver operator characteristic curves showed an average area under the curve of 0.70. The decrease in Pmsa due to the anesthesia-induced increase of the vascular compliance was fully compensated by the colloid fluid. A linear correlation between Pmsa and the volume changes suggested that the anesthesia increased the "unstressed" blood volume by 1.2 L. Conclusions. Pmsa was lower in fluid responders than in non-responders. General anesthesia increased the need for blood volume by 1.2 L.