[The effect of isoflurane or sevoflurane on circulating blood volume--study under spontaneous breathing]

Changes in circulating blood volume during isoflurane or sevoflurane anesthesia under spontaneous breathing were investigated by the dual indicator dilution method in 13 mongrel dogs. The animals were randomly divided into three groups; control (C) group n = 5, isoflurane (I) group n = 5, and sevoflurane (S) group n = 5. Changes in circulating blood volume (ml.kg-1) at 0, 0.5, 1.0 MAC were 87.7 +/- 8.2-->88.7 +/- 5.0-->91.0 +/- 5.9 in the I group and 84.4 +/- 7.0-->91.4 +/- 7.7-->91.4 +/- 10.2 in the S group, respectively. In the S group, circulating blood volume and plasma volume increased significantly, while in the I group the volumes tended merely to increase. Arterial carbon dioxide tension (PaCO2) in the I and S groups increased significantly at 0.5 and 1.0 MAC, but similar changes were also noted (not significantly) in the C group. Mean arterial pressure, mean pulmonary arterial pressure, and pulmonary capillary wedge pressure tended to increase at 0.5 and 1.0 MAC in the C and I groups, but tended to decrease in the S group. The results suggest that the increase in vascular compliance with sevoflurane under spontaneous breathing has resulted in the increase in plasma volume and circulating blood volume.