Difference in analgesia following epidural blockade in patients with postoperative or chronic low back pain

Subjective responses of continuous epidural analgesia with bupivacaine were compared in 30 patients with acute (postoperative) or chronic (low back) pain. In the acute pain patients, sensory block was 4 dermatomes at 9 h and 6 dermatomes at 64 h. Corresponding values in the chronic pain patients were 8 and 6 dermatomes respectively. Motor blockade of the lower limbs was more profound in the acute pain group. The acute pain patients had significantly better pain relief (VAS: 85-96% vs. 55-70%) and a significantly higher proportion of these patients reported a global score of 3 (excellent; 80% vs. 7%). The mean dosage of bupivacaine decreased in the acute pain group from 21.0 +/- 5.7 (mean +/- S.D.) mg/h at 9 h to 15.1 +/- 8.5 mg/h at 64 h. Corresponding values for the chronic pain group were 20.7 +/- 5.9 and 12.0 +/- 6.0 mg/h respectively. Mean plasma concentration of bupivacaine increased from 1.2 +/- 0.8 micrograms/ml at 9 h to 2.1 +/- 1.4 micrograms/ml at 64 h in the acute pain patients and was 0.8 +/- 0.3 micrograms/ml at 9 h to 1.0 +/- 1.0 micrograms/ml at 64 h in the chronic pain patients. The incidence of side effects was approximately the same in both groups. No signs of accumulation or toxic reactions to bupivacaine were seen.