Estimation of mean systemic filling pressure in postoperative cardiac surgery patients with three methods

PURPOSE: To assess the level of agreement between different bedside estimates of effective circulating blood volume—mean systemic filling pressure (Pmsf), arm equilibrium pressure (Parm) and model analog (Pmsa)—in ICU patients. METHODS: Eleven mechanically ventilated postoperative cardiac surgery patients were studied. Sequential measures were made in the supine position, rotating the bed to a 30° head-up tilt and after fluid loading (500 ml colloid). During each condition four inspiratory hold maneuvers were done to determine Pmsf; arm stop-flow was created by inflating a cuff around the upper arm for 30 s to measure Parm, and Pmsa was estimated from a Guytonian model of the systemic circulation. RESULTS: Mean Pmsf, Parm and Pmsa across all three states were 20.9 ± 5.6, 19.8 ± 5.7 and 14.9 ± 4.0 mmHg, respectively. Bland-Altman analysis for the difference between Parm and Pmsf showed a non-significant bias of −1.0 ± 3.08 mmHg (p = 0.062), a coefficient of variation (COV) of 15 %, and limits of agreement (LOA) of −7.3 and 5.2 mmHg. For the difference between Pmsf and Pmsa we found a bias of −6.0 ± 3.1 mmHg (p < 0.001), COV 17 % and LOA −12.4 and 0.3 mmHg. Changes in Pmsf and Parm and in Pmsf and Pmsa were directionally concordant in response to head-up tilt and volume loading. CONCLUSIONS: Parm and Pmsf are interchangeable in mechanically ventilated postoperative cardiac surgery patients. Changes in effective circulatory volume are tracked well by changes in Parm and Pmsa.