PurposeTo 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.MethodsEleven 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.ResultsMean 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.ConclusionsParm 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.

Pmsf can be determined in intensive care patients with an intact circulation with use of inspiratory pause procedures, making serial measures of circulatory compliance and circulatory stressed volume feasible.

The change in cardiac output induced by norepinephrine is determined by the balance of volume recruitment (increase in mean systemic filling pressure), change in resistance for venous return, and baseline heart function. Furthermore, the response of cardiac output on norepinephrine can be predicted by baseline stroke volume variation.

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