The effect of a standardized premedication on oxygen saturation in the cardiac patient before transfer to the operating room

The effect of premedication with morphine and scopolamine on arterial hemoglobin oxygen saturation (SaO₂) was measured continuously in 26 undisturbed patients in their hospital rooms before coronary artery bypass surgery. Two hours preoperatively each patient received morphine, 0.1 mg/kg, and scopolamine, 0.2 or 0.4 mg. SaO₂ was continuously recorded using pulse oximetry from one-half hour before premedication until 1 1 2 hours after premedication. The lowest SaO₂ measured both the evening before surgery and one-half hour before premedication was 95% ± 0.5% (mean ± SEM). After administration of premedication, the lowest SaO₂ for the patient population decreased to 93% ± 0.4% (P < 0.001 compared with that before premedication), and occurred 52 ± 2 minutes after premedication was given. Two patients (8%) had an SaO₂ < 90% (lowest SaO₂ for both was 88%). It is concluded that the dose of morphine/ scopolamine premeditation used was associated with a low risk of clinically important hypoxemia in the patient population studied.