No inhibition of intestinal motility after ketamine/midazolam anaesthesia. A study comparing the effects after enflurane and fentanyl/midazolam

Postoperative intestinal atonia is a complication which is likely to occur in patients predisposed for constipation and in patients after intra-abdominal operations. The postoperative delay of bowel movement, however, is often also related to the type of anaesthesia being used. In order to evaluate the magnitude of an anaesthetic-induced postoperative delay of bowel movement, two types of intravenous-based anaesthesia using fentanyl/midazolam (1 mg/25 mg; dosage 0.1 ml/kg/h), and ketamine/midazolam (250 mg/25 mg; dosage 0.1 ml/kg/h) respectively were compared with a volatile anaesthetic technique (enflurane; mean concentration 1.5 vol%). Methods. In three groups of patients (each n=15) undergoing elective surgery of the lower extremities, induction of anaesthesia was accomplished with methohexital (1 – 1.5 mg) followed by succinylcholine (1.5 mg/kg) to facilitate intubation. For the maintenance of muscle relaxation vecuronium bromide was used. All patients were given droperidol to prevent postoperative emesis, and they were artifically ventilated with N2O/O2 (60: 40) to normal end-expiratory CO2 concentrations. No anticholinergic agents were used at the end of operation since they are known to interfere with bowel motility. In order to determine gastro-intestinal motility, the H2 exhalation test was used. For this purpose 40 g lactulose in 100 ml of water was given to all patients via a gastral tube shortly before extubation. Lactulose is broken down by bacteria once it enters the colon, and H2 is released, taken up by the vascular system and exhaled. Postoperatively, patients were asked to exhale into a 20-ml syringe every 10 min. The content was analysed for hydrogen (ppm), using an electrochemical sensor (GMI exhaled hydrogen monitor). From the time of lactulose instillation to a threefold increase in endexpiratory hydrogen concentration (compared to the preoperative value), gastro-coecal transit time was computed. Results. All three groups of patients were comparable in age, height and body weight. Also, the duration of operation was comparable in all three groups. Mean gastro-coecal transit time was 204 (±19.6 SD) min following enflurane, 302 (±32.8 SD) min following fentanyl/-midazolam and 210 (±28.8 SD) min following ketamine/midazolam anaesthesia. The gastro-intestinal inhibition after the opioid-based anaesthetic technique was significantly prolonged (p<0.001, Kruskal-Wallis test). There was no significance between patients after ketamine-based anaesthesia and those who had the volatile anaesthetic. Discussion and conclusion. When using intravenous anaesthesia with an opioid, gastro-intestinal inhibition, especially in patients prone to have constipation, is likely to develop postoperatively. In classical neuroleptanaesthesia and in analgosedation in the ICU, the simultaneous use of the butyrophenone droperidol seems to counteract the inhibition of opioid-related gastrointestinal motility. In cases of opioid-related gastrointestinal atonia a gastrokinetic compound may be necessary to overcome this effect on intestinal motility.