Effect of Naloxone Infusion on Analgesia and Respiratory Depression after Epidural Fentanyl

The efficacy of two dosage regimens of intravenous naloxone were compared to avoid nonrespiratory side effects and respiratory depression and yet to preserve analgesia (maximum tolerance to periostial pressure over the tibia) after administration of 200 micrograms epidural fentanyl. Three groups of eight patients were studied: group 1 patients received a loading dose of 0.4 mg IV naloxone followed by naloxone infusion at a rate of 10 micrograms.kg-1.hr-1. Group II patients received a loading dose of 0.2 micrograms naloxone followed by a naloxone infusion at a rate of 5 micrograms.kg-1.hr-1. Group III patients received a saline infusion at a rate of 20 ml/hr. Epidural fentanyl significantly increased tolerance to periostial pain in all three groups (respectively, +38 +/- 20%, +36 +/- 16%, and +35 +/- 14%) (mean +/- SD; P less than 0.05). The naloxone infusion significantly reduced this effect in groups I and II, respectively, -40 +/- 20% and -37 +/- 28% below prenaloxone levels) (P less than 0.05). Nonrespiratory side effects were also reversed in groups I and II. In group III, neither periostial analgesia nor nonrespiratory side effects were affected. The baseline slopes of VE/PETCO2 were 2.34 +/- 1.01, 2.14 +/- 0.66, and 2.68 +/- 1.14 L.min-1.mm Hg-1, respectively, in groups I, II, and III. Epidural fentanyl significantly decreased the slope below baseline levels in each group: -21 +/- 16%, -22 +/- 17%, and -19 +/- 32%, respectively, in groups I, II and III.(ABSTRACT TRUNCATED AT 250 WORDS)