Oxycodone provided better analgesia but also more side effects, suggesting that the doses used in the present study may not be equipotent.

Subhypnotic doses of thiopentone are considered to have a hyperalgesic effect, while propofol has a hypoalgesic effect. We investigated the effect of these drugs on the nociceptive system by measuring the pain threshold to laser stimulation and the pain evoked potential (power and latency). Nineteen patients (ASA group I) participated. Twelve patients received thiopentone 0.5 mg kg-1 and propofol 0.25 mg kg-1 in random order separated by an interval of 14 h, and seven patients received saline. Immediately after the injection of both agents, the pain threshold was increased significantly (P less than 0.001) and the amplitude of the evoked potential was reduced significantly (P less than 0.05), while the latency of the evoked potential remained constant. It is concluded that, in subhypnotic doses, both thiopentone and propofol decrease the acute pain evoked by argon laser stimulation.

Subhypnotic doses of thiopentone are considered to have a hyperalgesic effect, while propofol has a hypoalgesic effect. We investigated the effect of these drugs on the nociceptive system by measuring the pain threshold to laser stimulation and the pain evoked potential (power and latency). Nineteen patients (ASA group I) participated. Twelve patients received thiopentone 0.5 mg kg-1 and propofol 0.25 mg kg-' in random order separated by an interval of 14 h, and seven patients received saline. Immediately after the injection of both agents, the pain threshold was increased significantly (P < 0.001) and the amplitude of the evoked potential was reduced significantly (P < 0.05), while the latency of the evoked potential remained constant. It is concluded that, in subhypnotic doses, both thiopentone and propofol decrease the acute pain evoked by argon laser stimulation.

In 20 patients a continuous block of the lumbar plexus was administered after knee-joint surgery, and the analgesic effect of two different concentrations of bupivacaine was compared. The same volume of bupivacaine was given to both groups of patients: a bolus dose of 0.4 ml/kg, 0.5% or 0.25%, followed by infusion of 0.14 ml/kg/h, 0.25% or 0.125%, respectively, via a catheter placed in the neurovascular fascial sheath of the femoral nerve according to the "3-in-1 block" technique. The median morphine consumption during the first 16 h postoperatively was 6.0 mg when bupivacaine 0.5/0.25% was used and 9.5 mg when 0.25/0.125% was used. This difference is not significant. The visual analogue pain scores were also similar in the two groups (P greater than 0.05). All plasma concentrations were below 4 micrograms/ml, the highest concentration measured being 3.6 micrograms/ml. It is concluded that when used for a continuous block of the lumbar plexus after knee-joint surgery, bupivacaine in a concentration of 0.125% offers the same pain relief as a concentration of 0.25%, and the risk of toxic reactions is reduced.

Analgesia was assessed quantitatively at various dermatomes (C7, T8, T10, T12, L1, L3, S1) for the first 30 min after subarachnoid administration of 0.5% bupivacaine 3.5 ml. Stimulation with 10 needles and laser stimulation could evoke pain in dermatomes with adequate analgesia to single needle stimulation. Analgesia was assessed by thresholds (sensory and pain) and by pain-related brain potentials (amplitude and latency) to laser stimulation. Little analgesia was found at T10, but it increased gradually towards caudal segments. The dermatome related to the site of the injection (L3) was not blocked to a greater extent than the surrounding dermatomes. Conduction time (the latency of the evoked brain potential) was increased relatively more from the S1 dermatome compared with L1.