Failure of epidural morphine to relieve pain in labour.

Lumbar epidural injections of 2 mg preservative-free morphine were given to 10 subjects in established labour. Assessment of pain using a visual analogue scoring system revealed no appreciable relief of pain 30 min after morphine infection. Analgesia was subsequently provided by epidural injection of 8 ml bupivacaine 0.375%. Failure of epidural 2 mg in the treatment of severe pain other than labour. Possible explanations for this discrepancy are discussed.