Incidence of arterial oxygen desaturation in cardiac patients premedicated with intramuscular scopolamine and morphine.

The effect of a standard preoperative medication combination, morphine and scopolamine, on arterial oxyhemoglobin saturation was measured continuously in 29 patients scheduled for elective coronary artery bypass grafting procedures. On the morning of operation, both before and after administration of preoperative medication, each patient was monitored continuously with a pulse oximeter (SpO2). Patients received 0.05 to 0.11 mg/kg of morphine (mean = 6.0 +/- 2.1 mg) intramuscularly (IM) and 0.2 to 0.4 mg of scopolamine (mean = 0.30 +/- 0.07 mg) IM. The mean arterial blood oxyhemoglobin saturation decreased from 92.0 +/- 1.8% before preoperative medication to 89.0 +/- 3.8% (P greater than .001) after preoperative medication. Forty-five percent of the patients had SpO2 less than 90% for at least 2 minutes, and 21% below 85%. In conclusion, significant arterial oxyhemoglobin desaturation occurred in this group of cardiac surgical patients after preoperative medication with morphine and scopolamine. Prophylactic administration of oxygen with preoperative medication might reduce the incidence of hypoxemia in this group of patients at risk for myocardial ischemia.