NO INHIBITION OF INTESTINAL MOTILITY AFTE R KETAMINE MIDAZOLAM ANESTHESIA - A STUDY COMPARING THE EFFECTS AFTER ENFLURANE AND FENTANYL MIDAZOLAM

Postoperative intestinal atonia is a complication which is likely to o ccur in patients predisposed for constipation and in patients after in tra-abdominal operations. The postoperative delay of bowel movement, h owever, is often also related to the type of anaesthesia being used. I n order to evaluate the magnitude of an anaesthetic-induced postoperat ive delay of bowel movement, two types of intravenous-based anaesthesi a using fentanyl/midazolam (1 mg/25 mg; dosage, 0. 1 ml/kg/h), and ket amine/midazolam (250 mg/25 mg; dosage 0.1 ml/kg/h) respectively were c ompared with a volatile anaesthetic technique (enflurane; mean concent ration 1.5 vol%). Methods. In three grups of patients (each n = 15) un dergoing elective surgery of the lower extremities, induction of anaes thesia was accomplished with methohexital (1-1.5 mg) followed by succi nylcholine (1.5 mg/kg) to facilitate intubation. For the maintenance o f muscle relaxation vecuronium bromide was used. All patients were giv en droperidol to prevent postoperative emesis, and they were artifical ly ventilated with N2)/O2 (60:40) to normal end-expiratory CO2 concent rations. No anticholinergic agents were used at the end of operation s ince they are known to interfere with bowel motility. In order to dete rmine gastro-intestinal motility, the H-2 exhalation test was used. Fo r this purpose 40 g lactulose in 100 ml of water was given to all pati ents via a gastral tube shortly before extubation. Lactulose is brocke n down by bacteria once it enters the colon, and H-2 is released, take n up by the vascular system and exhaled. Postoperatively, patients wer e asked to exhale into a 20-ml syringe every 10 min. The content was a nalysed for hydrogen (ppm), using an electrochemical sensor (GMI exhal ed hydrogen monitor). From the time of lactulose instillation to a thr eefold increase in endexpiratory hydrogen concentration (compared to t he preoperative value), gastro-coecal transit time was computed. Resul ts. All three groups of patients were comparable in age, height and bo dy weight. Also, the duration of operation was comparable in all three groups. Mean gastro-coecal transit time-was 204 (+/- 19.6, SD) min fo llowing enflurane, 302 (+/- 32.8 SD) min following fentanyl/-midazolam and 210 (+/- 28.8 SD) min following ketamine/midazolam anaesthesia. T he gastro-intestinal inhibition after the opioid-based anaesthetic tec hnique was significantly prolonged (p < 0.001, Kruskal-Wallis test). T here was no significance between patients after ketamine-based anaesth esia and those who had the volatile anaesthetic. Discussion and conclu sion. When using intravenous anaesthesia with an opioid, gastro-intest inal 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 butyroph enone 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 eff ect on intestinal motility.