What are the specific mechanisms by which ketamine, pethidine, and tramadol reduce shivering?
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Ketamine, pethidine, and tramadol each have specific mechanisms by which they reduce shivering, primarily through their effects on the central nervous system and thermoregulatory pathways.
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Ketamine
Ketamine is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist. Its mechanism of action in reducing shivering is believed to involve the regulation of thermoregulatory centers in the brain. By blocking NMDA receptors, ketamine can modulate the activity of noradrenergic and serotonergic systems in the locus coeruleus, which are critical for thermoregulation. This modulation helps to stabilize body temperature and reduce the incidence and severity of shivering post-anesthesia.
Pethidine (Meperidine)
Pethidine acts primarily through its effects on kappa (κ) opioid receptors. It reduces the shivering threshold by activating these receptors, which in turn decreases the body's response to cold stimuli. Additionally, pethidine has a sympathomimetic effect, which can help maintain hemodynamic stability and further contribute to its antishivering properties. However, pethidine also has side effects such as nausea, vomiting, and pruritus, which limit its use in some patients.
Tramadol
Tramadol works through multiple mechanisms to reduce shivering. It is a μ-opioid receptor agonist and also inhibits the reuptake of serotonin and norepinephrine. These actions help modulate the thermoregulatory process by affecting the central nervous system's response to temperature changes. Tramadol's ability to increase serotonin levels and inhibit norepinephrine reuptake contributes to its effectiveness in preventing and controlling shivering post-spinal anesthesia.
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In summary, ketamine reduces shivering by modulating NMDA receptors and thermoregulatory centers, pethidine acts through κ-opioid receptors and sympathomimetic effects, and tramadol works via μ-opioid receptor activation and modulation of serotonin and norepinephrine levels. Each of these mechanisms helps stabilize body temperature and reduce the incidence of shivering in patients undergoing spinal anesthesia.
