Instrumental Responses in Rats After Hypothermic Cardiopulmonary By-Pass. ∗

Summary

Fourteen lightly anesthetized (Nembutal) rats were cooled to a body temperature of 16°C and then connected to a pump oxygenator built especially for rats. Then the rats were cooled further to 14°C which induced respiratory arrest. The extra-corporeal blood flow of the hypothermic rats was 28 ml kg min (70% of the total cardiac output), while the delivery of oxygen was 1.7 ml/kg/min (100% of the total oxygen consumption). One to four hours later the animals were rewarmed to a body temperature of 25°C and the cardiopulmonary by-pass was then discontinued. Thereafter the animals were rewarmed to 37°C. All rats survived this cooling whereas all control animals without by-pass died. One day later the experimental animals were placed in a self-stimulating box. The animals had been trained before the by-pass to press a lever which induced electrical stimulation of their hypothalamic “pleasure center.” After the by-pass the rate of intracranial self-stimulation of all animals was the same as before by-pass. It is concluded that a 4-hour period of hypothermic cardiopulmonary by-pass with respiratory arrest does not induce any temporary or permanent neurological changes in rats as judged by their instrumental performance through intracranial self-stimulation.