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

Abstract

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.

Pharmacodynamic Analysis of a Fluid Challenge

“…The global effect of the fluid challenge on Pmsa was not different between groups, which is consistent with previous studies (22,39). Pmsa is an analogue of Pmsf, which should increase after intravascular volume expansion, regardless of cardiac function.…”

“…Pmsa calculation is based on the values of CO, CVP, mean arterial pressure (MAP), and patient's anthropometric measures (height, weight and age) (21,22).…”

“…There are other methods described to measure Pmsf (22) in patients with intact circulation but they are technically difficult to implement for a continuous monitoring of Pmsf.…”

Re: Mean systemic filling pressure: we can now estimate it but for what?

“…One answer, we agree, is that Pms is not easy to measure repeatedly using inspiratory hold or arm compression [2]. We have demonstrated [3] that a useful Pms analogue, Pmsa, can be calculated using…”

Predicting fluid responsiveness in ICU patients

“…Since the mean systemic filling pressure, relative to central venous pressure, is the driving pressure for venous return (and thus cardiac output), measuring mean systemic filling pressure, in combination with the cardiac function curve, can be helpful during hemodynamic management of spontaneously breathing patients [67,68]. In order to assess the mean systemic filling pressure at the bedside, several techniques are available [69].…”