Assessment of venous return curve and mean systemic filling pressure in postoperative cardiac surgery patients

Objective: To measure the relationship between blood flow and central venous pressure (P-cv) and to estimate mean systemic filling pressure (P-msf), circulatory compliance, and stressed volume in patients in the intensive care unit. Design: Intervention study. Setting. Intensive care unit of a university hospital. Patients: Twelve mechanically ventilated postoperative cardiac surgery patients. Interventions: Inspiratory holds were performed during normo-volemia in supine position (baseline), relative hypovolemia by placing the patients in 30 degree head-up position (hypo), and relative hypervolemia by volume loading with 0.5 L colloid (hyper). Measurements and Main Results: We measured the relationship between blood flow and P-cv using 12-second inspiratory-hold maneuvers transiently increasing P-cv to three different steady-state levels and monitored the resultant blood flow via the pulse contour method during the last 3 seconds. The P-cv to blood flow relation was linear for all measurements with a slope unaltered by relative volume status. P-msf decreased with hypo and increased with hyper (18.8 +/- 4.5 mm Hg, to 14.5 +/- 3.0 mm Hg, to 29.1 +/- 5.2 mm Hg [baseline, hypo, hyper, respectively, p < 0.05]). Baseline total circulatory compliance was 0.98 mL.mm Hg-1.kg(-1) and stressed volume was 1677 mL. Conclusions. P-msf can be determined in intensive care patents with an intact circulation with use of inspiratory pause procedures, making serial measures of circulatory compliance and circulatory stressed volume feasible. (Crit Care Med 2009; 37:912-918)