[Morphine concentrations in serum in need-controlled peridural morphine infusion].

After abdominal or thoracoabdominal operations, an epidural, on-demand morphine infusion following an initial bolus injection of 2 mg morphine was administered to 48 patients for postoperative pain relief. 34 non-intubated patients (Group I) and 14 artificially ventilated patients under intensive care conditions (Group II) received morphine solutions of 0.25% (maximum flow rate 0.31 ml/h) and 0.4% (maximum flow rate 0.5 ml/h), respectively. Total morphine consumption of the intensive care patients (Group II) until 8 p.m. on the 2nd postoperative day was 34.0 +/- 2.9 mg and was significantly higher than in non-intubated patients (Group I), with 6.4 +/- 0.4 mg (p less than 0.001). Although serum concentrations of free and metabolized morphine immunoreactivity declined in both groups in the course of treatment in accordance with the decreasing morphine demand, pharmacokinetics varied between the two groups. Whereas serum concentrations of free morphine immunoreactivity in group I, which decreased multiexponentially following the 2 mg. bolus injection, were not influenced by morphine infusion rates, serum morphine immunoreactivity in group II showed an increase until 8 p.m. on the operation day (p less than 0.005). Metabolized morphine reached plateau concentrations in both groups because of its relatively long half-life: the plateau in group II patients was significantly higher, was reached later and lasted longer than that of group I (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)