Effects on gastric emptying of thoracic epidural analgesia with morphine or bupivacaine.

The effects of thoracic epidural analgesia on gastric emptying were evaluated in healthy fasting volunteers. In ten volunteers, 4 mg of epidural morphine were injected at the T4 level, and ten volunteers received thoracic epidural analgesia with 0.5% bupivacaine, the latter causing block of the sympathetic innervation to the stomach. Acetaminophen absorption was used as an indirect measure of the rate of gastric emptying. After establishment of the analgesia with bupivacaine, or 160 (110-185) minutes after the administration of epidural morphine, 1.5 g acetaminophen dissolved in water was ingested. Serum samples were taken at 15-minute intervals for 2 hours and serum acetaminophen concentrations were determined by an immunologic method. Control acetaminophen absorption studies without thoracic epidural analgesia were performed in all 20 subjects on another occasion. During epidural analgesia with morphine mean serum acetaminophen concentrations were lower (P less than 0.05), the maximum serum acetaminophen concentration was lower (P less than 0.01), the time taken to reach the maximum concentration was longer (P less than 0.02), and the area under the concentration time curve from 0 to 60 minutes was smaller (P less than 0.01) than in the control study. The corresponding values during epidural analgesia with bupivacaine did not differ from the control values. Four subjects with extremely delayed gastric emptying during epidural analgesia with morphine showed no delay in gastric emptying after receiving 4 mg morphine intramuscularly. Serum morphine concentrations were lower after epidural than after intramuscular morphine. In summary, 4 mg epidural morphine delayed gastric emptying. This was not a systemic effect of morphine. Thoracic epidural analgesia with bupivacaine had no influence on gastric emptying.