Thermoregulation and Shivering

Opioid-based anesthesia probably reduces thermoregulatory thresholds to a degree similar to that of the potent inhaled agents.^{[137] [138]} However, meperidine is unique among opioids in its ability to effectively terminate or attenuate shivering in approximately 70% to 80% of patients.^{[139] [140]} The antishivering effect of meperidine is primarily related to a reduction in the shivering threshold^[141] and seems to be mediated by meperidine's activity on the κ-receptor.^[142] However, the relatively specific κ-receptor agonist nalbuphine did not show significant antishivering activity.^[143] A recent study has demonstrated that meperidine exerts agonist activity at the α_2B -adrenoreceptor subtype, suggesting this as a possible mechanism of this novel action in the antishivering action of meperidine.^[41] Alfentanil, morphine, and fentanyl are not as effective as meperidine in the treatment of postoperative shivering, although epidural opioid administration may reduce shivering in obstetric patients receiving regional anesthesia.^[144] Tramadol (0.5 mg/kg) suppressed postepidural anesthetic shivering in parturients as effectively as meperidine (0.5 mg/kg).^[145] Tramadol had

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