MYOELECTRIC ACTIVITY IN THE STOMACH AND DUODENUM AFTER EPIDURAL ADMINISTRATION OF MORPHINE OR BUPIVACAINE

Background: Gastric emptying is delayed in patients receiving postoper ative pain relief with epidural morphine compared to patients receivin g epidural bupivacaine. The electrophysiological basis for this effect is unknown. The aim of this study was to compare the effects of epidu ral morphine with epidural bupivacaine on gastroduodenal myoelectric a ctivity (EMG) in patients after surgery.Methods: Fourteen patients wit h epidural analgesia who underwent open cholecystectomy were randomly assigned to receive either epidural morphine (EM) or epidural bupivaca ine (EB) for postoperative pain relief. During surgery EMG electrodes were placed in the subserosa in the antrum and duodenum and the EMG re gistration started 3.5 hours after the end of surgery. Gastric emptyin g measured with the acetaminophen test was studied in the morning the day after surgery.Results: The spike activity in the antrum was signif icantly lower 160-340 minutes after the administration of morphine in the EM-group compared to the activity in the EB-group (P<0.04). The in cidence of regular slow wave rhythm in the antrum was significantly lo wer 160-520 minutes after the administration of morphine in the EM-gro up compared to the EB-group (P<0.03). Duodenal Phase III activity meas ured with EMG was significantly more frequent during 160-520 minutes a fter the morphine administration in the EM-group compared to the EB-gr oup (P<0.02). The acetaminophen absorption was significantly delayed i n the epidural morphine group compared to the epidural bupivacaine gro up. Conclusions: Gastroduodenal electromyographic activity was signifi cantly changed during epidural morphine compared to epidural bupivacai ne. The delayed gastric emptying during epidural morphine may be expla ined by decreased and uncoordinated contractile activity in the antrum , shown by decreased spike activity and irregular slow wave rhythm. Th e increased pressure activity in the duodenum, shown by increased Phas e III activity, may also impair gastric emptying.