Hemodynamic changes and regional blood flows responses to acute hemodilution and controlled hypotension were studied in 24 mongrel dogs anaesthetized with halothane and para-lized with pancuronium. Hemodilution was produced by 20 ml/kg removal of whole blood. The infusion of 6% Hydroxyethyl starch saline was started when 10 ml/kg of the whole blood was removed. The total infusion of 6% Hydroxyethyl starch saline was 20 ml/kg. Subsequently, hypotension was produced for 60 minutes by intravenous infusion of trimetaphan (TMP) or trinitroglicern (TNG), at mean arterial pressure of 60 mmHg. The following results were obtained :
1. In the hemodilution and TMP-induced hypotension group (the HD/TMP group), CI and renal cortical blood flow showed a significant decrease at 60 minutes of hypotension. The oxygen-carryjng capacity showed a significant decrease and oxygen extraction showed a gradual increase when hypotension was induced.
2. In the hemodilution and TNG-induced hypotension group (the HD/TNG group) MAP was not attained at the hypotension 60 mmHg (It was induced only 68 mmHg.) . CI was increased during hypotension. Renal cortical blood flow showed a significant decrease at hypotension of 60 minutes, however it was only slightly more than the HD/TMP group. Oxygen-carrying capacity showed no changes when hypotension was induced.
From these results, the HD/TMP group was superior to the HD/TNG group in the ability to control hypotension. And the HD/TNG group was safer than the HD/TMP group. However, the renal cortical blood flow of both groups showed a significant decrease at 60 minutes of hypotension. This method is necessary to increase the plasma volume expander.