European journal of anaesthesiology
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Randomized Controlled Trial Clinical Trial
Effects of S(+) ketamine added to bupivacaine for spinal anaesthesia for prostate surgery in elderly patients.
Intrathecal ketamine as the sole anaesthetic agent has demonstrated a lack of cardiovascular depression that should be of advantage in an elderly population. S(+) ketamine has three-times the analgesic potency of R(-) ketamine and its antinociceptive effects after intrathecal administration in rats are known. We decided to evaluate the effects of intrathecal S(+) ketamine added to a small dose of spinal bupivacaine in elderly patients undergoing transurethral prostate surgery. ⋯ Intrathecal S(+) ketamine administered with a low dose of bupivacaine provides shorter motor and sensory block onset time, shorter duration of action and less motor blockade in elderly males.
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The clinical practice of spinal morphine administration for pain relief is based on observations in animals that opioid receptors exist in the spinal cord and intrathecal injections of opioids in those species (mostly rats) lead to antinociceptive effects. Clinicians are well aware that administration of spinal opioids is associated with side-effects, such as nausea and respiratory depression, that indicate supraspinal spread of the drug administered. Those observations call into question how much of the observed pain relief is due to action of the drug in the brain. This study investigated the spinal cord actions of morphine given intrathecally to rats in a model that allows investigation of drug-receptor interaction at the spinal cord level. Experiments were performed on male Wistar rats with chronically implanted lumbar subarachnoid catheters. ⋯ Antinociception following intrathecal morphine involves spinal and supraspinal opioid receptors. The tail flick effect described in rat experiments involves actions at opioid receptors in the brain that override any action that may be caused by combination of morphine with mu-opioid receptors in the spinal cord.
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Clonidine has cardiac and systemic effects that can modify the potentially lethal cardiovascular effects of local anaesthetics. We evaluated the effects of clonidine pre-treatment on cardiotoxicity induced by an infusion of bupivacaine or ropivacaine and the success rate of resuscitation in anaesthetized rats. ⋯ Although pre-treatment with clonidine protects the effects of ropivacaine cardiotoxicity and increases the success rate of resuscitation, it does not affect bupivacaine toxicity.