The effects of epinephrine on lidocaine spinal anesthesia: a cross-over study.

The efficacy of epinephrine for prolonging the duration of lidocaine spinal anesthesia remains controversial. Seven volunteers were randomized in a double-blind manner to receive two 50-mg lidocaine (in dextrose 7.5%) spinal anesthetics with and without epinephrine (0.2 mg). Sensory analgesia was assessed with transcutaneous electrical stimulation (TES) equivalent to surgical incision and compared to standard pinprick dermatomal levels. Motor block was assessed with surface electromyography (EMG) and isometric force dynamometry. Intravenous fluids were administered by a standardized regimen, and time until ability to void was determined. Addition of epinephrine significantly prolonged duration of surgical anesthesia in the lumbar and sacral dermatomes by an average of 16-29 min (P = 0.03), but not in thoracic dermatomes. Although there was a trend toward prolongation of motor block with addition of epinephrine, this did not reach statistical significance. Epinephrine significantly prolonged duration until ability to void from 153 +/- 27 to 234 +/- 50 min (P = 0.0001). Thus, addition of epinephrine to lidocaine may be indicated to prolong duration of anesthesia for lower body operations. However, delayed recovery of ability to void may also prolong time until discharge after ambulatory surgery.

Opiate microinjections into midbrain do not affect the aversiveness of caudal trigeminal stimulation but produce somatotopically organized peripheral hypoalgesia.

High-dose microinjections of morphine sulfate (15 micrograms) and (D-Ala2)-Met-enkephalin (30 micrograms) were made into the ventral periaqueductal gray of rats. Consistent with previous reports using lower doses, both opiates produced hypoalgesia for noxious thermal stimuli applied to the upper and lower body. More hypoalgesia was observed on the face than on the hind legs or tail. Current thresholds of aversive reaction to stimulation in the trigeminal subnucleus caudalis were unaffected by microinjection of either opiate. Systemic injections of 6 mg/kg morphine sulfate profoundly inhibited defense responses to peripheral noxious stimuli and significantly elevated aversive reaction thresholds for stimulation in the trigeminal subnucleus caudalis. Aversive reactions to stimulation in the dorsal periaqueductal gray remained unaffected by either microinjected or systemically administered opiates.