Cerebrospinal norepinephrine concentrations and the duration of epidural analgesia.

This study was performed to determine whether the addition of norepinephrine to local anaesthetics prolongs epidural analgesia in man. In addition, cerebrospinal fluid norepinephrine (NE) concentrations were measured. In the first part of the study, epidural catheters were inserted in 14 patients before herniotomy. Mepivacaine, 1.5 per cent (0.35 ml.kg-1), was administered and norepinephrine (5 micrograms.ml-1) was added in seven patients. The duration of anaesthesia was prolonged from 54 +/- 11 min to 83 +/- 12 min (P less than 0.05) and CSF NE concentrations increased from 68 +/- 12 pg.ml-1 to 336 +/- 85 pg.ml-1 in the NE group (P less than 0.01). In the second part, eight patients with herpetic neuralgia received epidural analgesia at the fourth to eighth thoracic interspace, using bupivacaine 0.25 per cent, with and without NE. The CSF NE concentrations in this group were greater than in the surgical patients before operation and increased from 254 +/- 58 to 406 +/- 58 pg.ml-1 30 min after administration of bupivacaine with NE. The duration of pain relief was prolonged with NE. These results suggest that adding NE to local anaesthetics prolongs epidural analgesia. Moreover, NE concentrations in surgical patients increased to levels similar to those found in patients suffering from herpetic analgesia. This suggests that the increase of CSF NE in chronic pain states has an antinociceptive effect.