British journal of anaesthesia
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Randomized Controlled Trial Comparative Study Clinical Trial
Peripheral lidocaine but not ketamine inhibits capsaicin-induced hyperalgesia in humans.
We examined the effect of the subcutaneous infiltration of ketamine, lidocaine and saline before injury on capsaicin-induced pain and hyperalgesia. Twelve healthy volunteers participated in two separate, randomized, double-blind, placebo-controlled crossover experiments. In experiment 1, 100 micrograms capsaicin was injected intradermally in one volar forearm 10 min after the skin had been pretreated with lidocaine 20.0 mg in 2.0 ml or 0.9% saline 2.0 ml at the capsaicin injection site. ⋯ Pain scores and areas of hyperalgesia were not affected when the contralateral site was infiltrated with ketamine or lidocaine. Lidocaine produced no side-effects, whereas ketamine produced paraesthesia, dizziness and sleepiness in six out of 24 (25%) cases. Blocking peripheral sodium channels with locally administered lidocaine reduces spontaneous pain and capsaicin-induced hyperalgesia but local block with the NMDA-type glutamate receptor antagonist ketamine has no effect on capsaicin-induced pain and hyperalgesia.
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A 46-yr-old man with dysaesthesia (burning sensation) following herpes zoster in the left upper chest region was treated with a single thoracic (T2/T3) epidural injection (1.0% lidocaine 3 ml + 0.125% bupivacaine 3 ml) as an outpatient. Twenty minutes after the injection, a nurse noticed the patient to be unconscious with dilated pupils, apnoea and cardiac arrest. Following immediate cardiopulmonary resuscitation, the patient was treated with an i.v. infusion of thiamylal sodium 2-4 mg kg-1 h-1 and his lungs were mechanically ventilated. ⋯ Weaning from the ventilator was successful on the 18th day. About 4 months after the incident, the patient was discharged with no apparent mental or motor disturbances. We suggest that mild hypothermia with barbiturate therapy may have contributed to the successful outcome in this case.
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We investigated the significance of pre-emptive analgesia using a well-known model of neuropathic pain in rats. Lignocaine, bupivacaine or saline was applied locally to the left L5-L6 spinal nerve before or 4 days after nerve injury. ⋯ However, this effect lasted only 24 h. Our study in rats questions the beneficial effect of a single dose of local anaesthetic as pre-emptive analgesia.
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Comment Letter Case Reports
The interscalene approach to the cervical plexus.