Influence of epinephrine as an adjuvant to epidural morphine.

The effects of epinephrine 1/200,000 as an adjuvant to epidural morphine were investigated in three healthy male volunteers, during 26-h observation sessions. Peak blood concentrations of morphine were 44 +/- 12.9 ng/ml after plain morphine and 13.7 +/- 6.7 ng/ml after epinephrine-morphine. Cutaneous hypalgesia was more intense, faster in onset, and longer in duration after epinephrine-morphine than after plain morphine, and analgesia to ice-water immersion of extremities lasted longer. Adverse side effects of pruritus, nausea, vomiting, and difficulty of micturition were also more intense after epinephrine-morphine, and respiratory sensitivity to CO2 was depressed more severely between 6 and 16 h. The results indicated that epinephrine 1/200,000 reduces vascular absorption of epidural morphine and intensifies all the manifestations of cord and brainstem uptake.