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 less than 0.001 compared with that before premedication), and occurred 52 +/- 2 minutes after premedication was given. Two patients (8%) had an SaO2 less than 90% (lowest SaO2 for both was 88%). It is concluded that the dose of morphine/scopolamine premedication used was associated with a low risk of clinically important hypoxemia in the patient population studied.