Respiratory depression and morphine concentration in serum after epidural and intramuscular administration of morphine.

The ventilatory response to carbon dioxide and the serum level of free morphine were measured in six adult patients scheduled for operation under lumbar epidural analgesia. The investigation was performed on 2 consecutive days before the operation. The measurements were performed before, and 30 and 90 min after the intramuscular administration of morphine chloride (0.15 mg/kg body weight) as well as lumbar epidural administration of morphine chloride (5 mg morphine chloride diluted in 10 ml isotonic saline). The ventilatory response to carbon dioxide was depressed significantly both 30 and 90 min after epidurally administered morphine compared to the control value, while the depression of the ventilatory response was demonstrated in only five of six patients 30 min after intramuscularly administered morphine. The peak serum levels of free morphine were reached within 20 min of administration and it seemed that the injected quantity of morphine and not the method of administration determined the serum level.