Hypercarbia During Light Halothane Anesthesia with Neuromuscular Block

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Abstract
In conscious human subjects when the CO2 tension of the blood rises there is an early response by the respiratory and cardiovascular system. The cardiovascular response appears to be independent of the extent of the ventilatory effort. With neuromuscular block there is obviously no ventilatory response. The detailed cardiovascular response is therefore clinically important. Ten children, after standard premedication, were anesthetized with 50% nitrous-oxide and 0.5% halothane by inhalation and a continuous intravenous infusion of succinyl-choline chloride maintained muscle paralysis. Artificial ventilation was maintained at an adequate standard. CO2 was inhaled for 10 minutes. Arterial pH and PCO2 was measured and cardiac output determined by dye dilution before during and after CO2 addition. Electrocardiogram and arterial blood pressure were recorded continuously. Blood epinephrine and norepinephrine levels were estimated during hypercarbia in 5 patients. With an average increase of 20 mm. of mercury arterial PCO2 there was no statistically significant change in any of these parameters or the computed systemic resistance.