[The agonist-antagonist nalbuphine prolongs gastro-cecal transit time and induces short-term pain following neuroleptanesthesia using fentanyl. A comparative study using a placebo].

Little is known about the effects of mixed opioid analgesics on gastrointestinal propulsion. In 20 patients, nalbuphine (0.1 mg/kg) was given after routine neuroleptanesthesia consisting of 70 micrograms/kg droperidol, 7 micrograms/kg fentanyl, and N2O/O2 (3:1) ventilation, to study its effect on gastrointestinal motility in the postoperative period. For comparison, another group of patients (n = 20) undergoing similar interventions received placebo (0.9% NaCl) at the end of the procedure. Gastrointestinal transit time was determined by measuring the exhaled H2 concentration following gastric lactulose administration. As lactulose is degraded only in the cecum, resulting in the release of hydrogen, the arrival of the polysaccharide at the terminal ileum could thus be determined. Compared to placebo, gastrointestinal transit was significantly longer in patients after nalbuphine (mean transit time 270 min vs 380 min). Pain estimation by visual analogue scale (VAS 0-10) suggested an antagonistic effect at the 10th and 20th min postoperatively, as pain scores in the nalbuphine group were higher when compared to placebo (3.5 vs 1.8 and 2.5 vs 1.4). There was a similar pain score in both groups (1.3 vs 1.4) 30 min after drug administration. However, there was significantly better pain relief after nalbuphine (0.7 vs 1.4 and 0.7 vs 1.1) in the late postoperative period (120th and 240th min). When given after potent opioids, it must be borne in mind that the antagonistic effect of nalbuphine is initially apparent. The agonistic potency of the compound will come into effect around the 30th min post-injection. Delayed gastrointestinal transit after nalbuphine is explained by agonist-like effects on peripheral opioid receptors in the gut.