[Nalbuphine after enflurane or fentanyl--effect on circulation and respiration]

The agonistic and antagonistic properties of nalbuphine were examined in 80 surgical patients after anaesthesia consisting essentially of flunitrazepam/enflurane or flunitrazepam/fentanyl. After the operation the intubated and still unconscious patients were breathing either N2O/O2/enflurane 0.4 Vol.% or N2O/O2 (FIO2 0.33). The mean fentanyl requirement during operation was 0.55 microgram/kg body weight/10 min anaesthesia. The respiratory minute volumes (RMV) were similar in all groups and ranged between 77-89% of the calculated normal value. The respiratory rate was 18-23/min in the enflurane groups and 11-12/min in the fentanyl groups. After reaching a circulatory and respiratory steady state, nalbuphine was administered i.v. in the doses of 2.5, 5, 10 or 20 mg. In the enflurane groups nalbuphine produced a pure depressant effect on respiratory parameters. The RMV decreased by 27 +/- 3%, the calculated alveolar ventilation by 20-24% and the breathing rate by 6 breath/min. A new steady state was reached within 10 min. The well-known ceiling effect was observed. In contrast to the observations in awake patients the maximum depressant effect was already reached after a dose of only 5 mg nalbuphine. Arterial blood pressure decreased by 4-5 mmHg and heart rate by 5 beats/min. After fentanyl, however, nalbuphine in all doses exhibited a stimulating effect on respiration and circulation. A steady state was reached after 10 min as well. A maximum effect on alveolar ventilation (+ 39 +/- 8%) was obtained after 5 mg nalbuphine and did not increase further with increasing doses. The effects on RMV and on respiratory rate were dose dependent. Arterial blood pressure increased slightly as did heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)