Influence of ketamine anesthesia on cardiac output and tissue perfusion in rats subjected to hemorrhage.

Ketamine anesthesia has been considered suitable for use in patients suffering from acute hypovolemia. Using a microsphere technique, fractional distribution of cardiac output and tissue perfusion were determined in rats subjected to moderate (10 ml/kg), or severe (bled to 60 torr systolic arterial pressure) hemorrhage. In the moderate bleeding bleeding experiments, rats under ketamine anesthesia were compared to awake rats as well as to awake normovolemic rats. In the severe bleeding experiments, rats under ketamine anesthesia were compared to rats under barbiturate anesthesia. Following moderate bleeding the ketamine group had a significantly large cardiac output and higher arterial pressure than the unanesthetized group. There were no major differences in the fractional distribution of cardiac output, although tissue perfusion in the ketamine group was significantly larger in heart, kidneys, skin, and small intestine. The shed blood volume necessary to reach 60 torr in systolic arterial pressure was 36 per cent of normal blood volume in the ketamine group, and 23 per cent in the barbiturate group. In spite of the greater blood loss, rats under ketamine anesthesia displayed significantly larger cardiac output and a higher elevation of arterial pressure 20 min after the hemorrhage. In the ketamine group, fractional distribution of cardiac output favored the internal organs as opposed to an increase in the carcass in the barbiturate group. The ketamine anesthetized rats had a significantly larger perfusion to most organs, including heart, kidneys, and brain. It is concluded from this study that in rats experiencing acute hypovolemia blood flow to vital organs and cardiac output are well maintained under ketamine anesthesia.