Peripheral Vascular Volumes and Whole Body Hematocrit During Human Heart Lung Bypass

Indicator-dilution curves were obtained across the peripheral vascular bed in 15 patients soon after the beginning of heart lung bypass, and in eight of these persons they were repeated just prior to the conclusion of bypass. A bolus containing labelled red cells and albumin was injected into the arterial inflow line just proximal to the aorta. Serial blood samples were obtained at intervals of 1 second from the venous return line, just distal to the right atrium, and the radioactivity was measured. The interposed volume of blood in the pump oxygenator delayed recirculation, allowing extrapolation of the exponential downslope and calculation of flow rates and indicator distribution volumes by the Hamilton-Stewart equations.The distribution volume of albumin (average, 56.3 ml/kg) was always greater than that of red cells (average, 44.8 ml/kg). The average ratio of whole body hematocrit to perfusate hematocrit was 0.873. The absence of significant differences between data obtained at the beginning and just prior to the end of bypass suggests that there were no alterations in venous tone or the volume relationships of large vessels to the microcirculation.