A new model of electrically evoked pain and hyperalgesia in human skin - The effects of intravenous alfentanil, S(+)-ketamine, and lidocaine

Background The authors used the analgesics alfentanil, S(+)ketamine, and sy stemic lidocaine to examine a new human model of experimental pain and hype ralgesia. Methods: Transcutaneous electrical stimulation at a high current density (5 Hz, 67.5 +/- 6.6 mA) was used to provoke acute pain (numeric rating scale, 5 of 10), stable areas of secondary mechanical hyperalgesia to pin prick ( 43.6 +/- 32.1 cm(2)), and light touch (27.5 +/- 16.2 cm(2)) for 2 h. Alfent anil, S(+)-ketamine, and lidocaine were applied for 20 min in a double-blin d, placebo-controlled, crossover design in 12 subjects using target control led infusions. Results: In the placebo session, pain ratings and areas of hyperalgesia wer e stable during the stimulation period, which facilitated the assessment of analgesic effects. Alfentanil effectively inhibited electrically evoked pa in and reduced pin prick hyperalgesia and allodynia during its infusion. S( +)-ketamine-induced inhibition of secondary hyperalgesia was more pronounce d and lasted for the whole experimental protocol. Therapeutic levels of sys temic lidocaine showed only marginal analgesic effects, but lasting antihyp eralgesic effects. Conclusions: A new model of electrically induced pain and hyperalgesia was established, which enabled assessment of the time course of analgesic and a ntihyperalgesic effects with high temporal resolution and minimum tissue da mage and which was further validated by use of common intravenous anestheti cs.