THE IMMEDIATE DECREASE IN BLOOD PRESSURE SEEN AT THE CONCLUSION OF CYCLOPROPANE ANESTHESIA

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Abstract
The cause of the sudden fall of blood pressure, frequently noted at the conclusion of cyclopropane anesthesia, was investigated in adult patients. Twenty subjects were studied under cyclopropane anesthesia; 2 received Na pentothal intraven., and to one diethyl ether was administered. Minute vol. of the expired air, respiratory rate, blood pressure, and pulse rate were recorded. The pH of the whole blood was detd. with a glass electrode. CO2 content, O2 content, and O2 capacity of the blood were detd. by the manometric technic of Van Slyke and Neill. The CO2 tension (pCO2) was calculated according to the Hasselbalch equation. Cyclopropane cone, in arterial blood was detd. by the method of Orcutt and Waters. Blood for all detns. was taken from the brachial or radial artery. In 10 of 11 patients who received cyclopropane anesthesia, the pCO2 was definitely elevated at the end of the operation with an associated drop in pH of the arterial blood. Nine of these patients showed a drop in blood pressure after removal of the mask. There was a definite relationship between CO2 accumulation in the blood at the end of the anesthesia and the blood pressure drop after the removal of the mask. The blood pressure fall could be prevented by postanesthetic inhalation of CO2. No comparable drop of blood pressure was observed after pentothal or ether anesthesia. On the basis of these expts. and the findings of other workers, it seems probable that the blood pressure fall observed at the conclusion of cyclopropane anesthesias is due to the sudden removal of the accumulated CO2 from the blood. Other physiologic imbalances secondary to the closed system method of admn. may also be concerned in the postanesthetic blood pressure decrease.