Oxygen transport during hemodilution in normoxic and hypoxic dogs treated with verapamil

In order to determine the possible limitations of acute isovolemic hemodilution in patients taking verapamil, the various factors determining oxygen availability were analyzed in an animal experiment. Twenty-four anaesthetized dogs were subjected to a gradual isovolemic hemodilution. Six dogs received a bolus injection of 0.1 mg kg-1 of verapamil followed by 0.01 mg kg-1 min-1. In 12 dogs, mild hypoxic hypoxia was induced by ventilation with 16-17% oxygen; six of them also received verapamil. Six dogs served as a control group. In the latter, due to an increase in heart rate and stroke volume, oxygen availability in the clinically relevant range of hemodilution between HC 25 and 25% was maintained at 81% of its control value. In normoxic animals treated with verapamil, oxygen availability decreased more rapidly and was below the level of the control group once HC reached 25%. Mild hypoxic hypoxia alone did not reduce oxygen availability as much as its combination with verapamil. Even though the verapamil-induced reduction in oxygen availability was similar during normoxia and hypoxia, the sharp rise in serum lactate at HC levels below 35-30% in the hypoxic verapamil group was a sign of impairment of tissue oxygenation. Hematocrit levels below 35-30% and even moderate hypoxemia should be avoided whenever the cardiovascular response to hemodilution is influenced by verapamil.