BEDSIDE ASSESSMENT OF INTRAVASCULAR VOLUME STATUS IN PATIENTS UNDERGOING CORONARY-BYPASS SURGERY

Background: Management of intravascular volume is crucial in patients after cardiopulmonary bypass as myocardial dysfunction is common. The purpose of this study was to validate a novel bedside technique for re al-time assessment of intravascular volumes. Methods: Eleven patients undergoing cardiopulmonary bypass were studied. In addition to standar d monitors, a fiberoptic thermistor catheter was placed in the descend ing aorta and central venous injections of 10 ml ice-cold indocyanine green dye were performed. Total blood volume was measured by a standar d in vitro technique. Circulating and central blood volume were calcul ated by using cardiac output, mean transit times, and a newly develope d recursive convolution algorithm that models recirculation. Measureme nts were performed after induction of anesthesia and at 1, 6, and 24 h after surgery. Results: A two-compartment model of the circulation wa s required for adequate fit of the data. We found a significant correl ation between total and circulating blood volumes (r = 0.87). One hour after surgery, central blood volume was decreased by 10% (P < 0.05). At 6 and 24 h after surgery, circulating blood volumes were significan tly increased by 29% and 20%, respectively (P < 0.01), although centra l blood volume was similar to control values. Before surgery stroke vo lume index correlated with circulating blood volume (r = 0.87) but not with pulmonary capillary wedge and central venous pressures. Conclusi ons: This study shows that bedside determinations of intravascular blo od volumes are feasible and that these measurements are more indicativ e of intravascular volume status than are either pulmonary capillary w edge or central venous pressures in the post-cardiopulmonary bypass pe riod. Our data also demonstrate that despite a normal central blood vo lume both circulating and total blood volume are significantly increas ed in the immediate post-cardiopulmonary bypass period.