Addition of fentanyl to epidural lidocaine raises the toe temperature

In order to investigate effects of addition of fentanyl epidurally on the onset of sympathectomy from epidural lidocaine, we have measured the toe temperature of 29 healthy patients undergoing elective lower extremity or lower abdominal surgeries. The latency of onset of the toe temperature was significantly shorter in patients receiving both epidural lidocaine and fentanyl compared with those receiving epidural lidocaine alone (258 +/- 135 vs 398 +/- 184 sec, P < 0.05 mean +/- SD]). Osmolarity and pH of the epidural solutions were similar between the two groups. These results suggest, but do not indicate, that sympathectomy from epidural lidocaine is accelerated by the addition of fentanyl.