Monitoring intravascular volumes for postoperative volume therapy

Abstract

Background and objective: The feasibility of monitoring measured intravascular volumes and the cardiac filling pressures were compared to reflect the optimal volume status of postoperative patients.

Methods: In a prospective clinical study, 14 hypovolaemic adult patients were included after cardiac surgery. All patients received 1000 mL hydroxyethyl starch after meeting the authors’ criteria for hypovolaemia. Pressures were measured by use of a pulmonary artery catheter and volumes were determined by double-indicator dilution technique.

Results: Stroke volume index (SVI), central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), intrathoracic blood volume index (ITBVI) and total circulating blood volume (TBVI_circ) increased significantly after volume loading (30.7 ± 9.8 to 41.7 ± 9.6 mL m⁻², 4.9 ± 1.7 to 9.1 ± 2.3 mmHg, 6.6 ± 1.3 to 10.6 ± 1.9 mmHg, 858 ± 255 to 965 ± 163 mL m⁻², and 1806 ± 502 to 2110 ± 537 mL m⁻², respectively). During the subsequent 1 h steady-state period, CVP and PAOP decreased significantly (9.1 ± 2.2 to 7.4 ± 2.2 mmHg and 10.6 ± 1.9 to 9.2 ± 2.0 mmHg, respectively), whereas SVI and intravascular volumes remained unchanged. The changes of CVP and PAOP did not correlate with changes in stroke volume during volume loading (r² = 0.06 and 0.03, respectively) and during steady-state (r² = 0.17 and 0.00 respectively). On the other hand, a significant correlation was found between changes of the intrathoracic blood volume and changes in stroke volume during the volume loading (r² = 0.67) and also during the steady-state phase (r² = 0.83).

Conclusions: Intrathoracic blood volume reflects more accurately the preload dependency of cardiac output in postoperative patients than left/right-sided cardiac filling pressures.