[Respiratory depression after fentanyl and antagonism by naloxone (author's transl)]

The postoperative respiratory depressant effect of fentanyl in combination with flunitrazepam (Rohypnol) was assessed in awake and in unconscious patients. In awake patients respiratory function was measured with blood-gas analyses. For measurements in unconscious patients the administration of nitrous oxide/oxygen was continued postoperatively and the respiratory depression was judged from the increase in respiratory minute volume after the i.v. administration of 0.05 mg naloxone (Narcan). In the group of awake patients blood-gasvalues were within the normal range after anaesthesia with flunitrazepam (1 mg) and fentanyl (0.80 mcg/kg body weight/10 min anaesthesia; last fentanyl given 40 min before the end of the operation), and the administration of naloxone was without any effect. If, however, naloxone was given while the patients were kept under light nitrous oxide/oxygen anaesthesia, the effect was different. The respiratory minute volume was considerably less than its predicted value in all groups of patients having received fentanyl, and naloxone caused a marked increase in respiratory minute volume and in respiratory rate. In a group of patients which have received no opiate but enflurane, naloxone showed no effect. After premedication with pethidine as compared with flunitrazepam the effect of naloxone on ventilation was more pronounced. This marked difference in the postoperative effect of fentanyl on ventilation depending on the state of consciousness has to be attributed to an interaction between a residual respiratory depressant effect of fentanyl and the effect of unconsciousness. Since after the combined use of flunitrazepam and fentanyl deep postoperative sleep occurs quite frequent, a residual effect of fentanyl should always be antagonized with naloxone to protect the patients from a possible hazardous effect of this interaction.