Epidural lidocaine delays arousal from isoflurane anesthesia

To clarify the effect of epidural lidocaine on arousal from inhaled anesthesia, we investigated the minimum alveolar anesthetic concentration at awakening (MAC-Awake) of isoflurane and the duration between discontinuance of isoflurane inhalation and arousal from anesthesia in 60 female abdominal hysterectomy patients. All patients received epidural catheterization and were randomly assigned to one of five groups. The control group, A, was given normal saline intravenously (IV) and epidurally. Group B was given 1 mg/kg of 2% lidocaine IV as a bolus. Groups C and D were given 0.5 and 1 mg/kg, respectively, of 2% lidocaine IV for 5 min, followed by 30 micrograms.kg-1.min-1. Group E was given 3 mg/kg of 1.5% lidocaine epidurally as a bolus. These doses of lidocaine or control saline were administered 15 min before the end of the surgical procedure. MAC-Awake values in Groups A, B, C, D, and E were 0.30% +/- 0.05%, 0.28% +/- 0.04%, 0.29% +/- 0.04%, 0.31% +/- 0.04%, and 0.18% +/- 0.05% (mean +/- SD), respectively. MAC-Awake in Group E was lower than in the other groups (P < 0.001). The duration until arousal in Group E (21.0 +/- 2.0 min) was longer than in Groups A, B, C, and D (12.6 +/- 1.8 min, 12 +/- 2.3 min, 13.3 +/- 2.5 min, and 14.3 +/- 2.7 min, respectively) (P < 0.001). Plasma lidocaine levels in Groups B, C, D, and E were 0.95 +/- 0.17 microgram/mL, 1.07 +/- 0.16 microgram/mL, 2.09 +/- 0.31 micrograms/mL, and 1.02 +/- 0.16 micrograms/mL, respectively. We conclude that analgesia produced by epidural lidocaine delays arousal from isoflurane anesthesia. Furthermore, lidocaine plasma levels are shown to be too low to cause any sedative effect, thus suggesting that postoperative pain may cause significantly faster arousal from anesthesia.