Rostral Spread of Epidural Morphine

Abstract

Healthy males (10) 18-33 yr old received 10 mg morphine sulfate i.v., or by lumbar epidural injection at 2 sessions 2-4 wk apart, in random sequence. Few nonrespiratory changes were seen after i.v. morphine. Cold pressor response was unchanged in hand and foot, no segmental hypalgesia or itching occurred and only 1 subject complained of nausea. Marked changes occurred after epidural morphine. Cutaneous hypalgesia to ice and pin scratch appeared in the thoracolumbar region in all subjects. In 6 subjects hypalgesia rose to the midthoracic region during the 2nd or 3rd h and to the trigeminal distribution between the 6th and 9th h in 5 subjects. Cold pressor response fell rapidly in the foot during the first 1.5 h after epidural morphine, and a little later cold pressor response also fell in the hand in all subjects, remaining depressed for the duration of the experimental period. Pruritus occurred at 3 h in 9 of the 10 subjects, nausea at .apprx. 4 h in 6 subjects, and vomiting at .apprx. 6 h in 5 subjects. Hypalgesia and side effects were not related to serum concentrations of morphine. Evidently lumbar epidural morphine travels cephalad in the CSF to reach the brain stem and 4th ventricle by the 6th h.