[The effect of isoflurane or sevoflurane on circulating blood volume--a study under controlled ventilation]

Changes of circulating blood volume during isoflurane or sevoflurane anesthesia were investigated by the dual indicator dilution method in eighteen mongrel dogs. The animals were randomly divided into three groups; control (C) group n = 6, isoflurane (I) group n = 6, and sevoflurane (S) group n = 6. The values of circulating blood volume (ml.kg-1) at 0, 0.5 and 1.0 MAC period were 90.1 +/- 18.7----87.5 +/- 17.2----94.1 +/- 23.6 in the I group and 91.6 +/- 12.5----96.5 +/- 15.0----94.1 +/- 8.5 in the S group, respectively. No significant changes were found in both groups concerning circulating blood volume, red cell volume, and plasma volume, but circulating blood volume and plasma volume tended to increase slightly in both groups at 0.5 and 1.0 MAC period compared with 0 MAC period. Mean arterial pressure decreased 68% of the initial value in the I group at the 1.0 and 78% stages in the S group. Cardiac index tended to increase from 2.6 +/- 0.4 l.min-1.m2 to 3.2 +/- 0.9 in the I group at the stage 1.0 but to decrease from 5.2 +/- 1.4 l.min-1.m2 to 4.1 +/- 0.9 in the S group. It was suggested that the increase of venous pressure resulted in the significant decrease of plasma volume. Increase of intrathoracic pressure during positive pressure ventilation might partially influence the blood volume change. Our data suggest that isoflurane and sevoflurane do not greatly affect the circulating blood volume under control ventilation.