[Postoperative, opiate-induced respiratory depression is not dependent on arousal]

Respiratory depression after intravenous anesthesia is supposed to be related to vigilance. This hypothesis could not yet be tested because of the lack of methods measuring continuously important parameters of respiration without altering the patient's vigilance. Pulse Oximetry offers this possibility. The following study was performed to investigate the effects of the Benzodiazepine Antagonist Flumazenil (Anexate) on parameters of vigilance and respiration after Midazolam/Fentanyl anesthesia.

40 healthy patients aged 18-65 years who were to undergo arthroscopy were randomly assigned to Flumazenil (Group F) or no Flumazenil = Control (Group C). All patients received 7.5-10 mg Midazolam, 0.3-0.6 Fentanyl, 4-6 mg Vecuronium, were intubated and ventilated with 8 ml/kg BW VT x 12/min - N2O/O2 = 2:1. At the end of operation Group F received 0.3-0.5 mg Flumazenil. When adequate spontaneous ventilation was restored the patients were extubated and brought to a single bed room where they were monitored and observed without being disturbed, except at the arrival time (T1), 15 min (T2) and 30 min (T3) when blood pressure was measured and the pain score was asked. The following parameters were registered: Transcutaneous Oxygen Saturation (SAT) and Heart Rate (HR) continuously, Sedation (every minute) and Reactions to acoustic or verbal stimuli in the case of hypoxemia. The two groups were compared with respect to the number and severity of hypoxic events/15 min, the mean degree of sedation (6 point scale) and the number of adequate reactions to the acoustic alarm resp. instruction: "Take a deep breath!"

Wilcoxon Test, Chi-Square test (p less than or equal to 0.05) is significant).

The groups were comparable with respect to their anthropometric data, dosages of Midazolam and Fentanyl, and perioperative blood pressures. Parameters of vigilance: Group F was less sedated than Group C (p = 0.052) and reacted better to the verbal instruction to take a deep breath in the case of hypoxia (p less than or equal to 0.05). Parameters of respiration: Hypoxic states occurred more frequently in group F (p = 0.098) and lasted longer. The severeness was significantly more pronounced in group F (p less than or equal to 0.05). There were no complications and the patients acceptance of the anesthetic procedure was high.

The hypothesis that postoperative respiratory depression is related to the degree of vigilance cannot be accepted. In contrast there is a strong evidence that under special conditions patients can be in a relatively high degree of vigilance and do not breathe with subsequent severe hypoxemia. The possible u