Shivering associated with general anesthesia using remifentanil]

General anesthesia using remifentanil is accompanied with post-operative shivering at a high incidence. Post-operative shivering can be divided into thermoregulatory and non-thermoregulatory. Hypothermia causes thermoregulatory shivering. The interthreshold range is defined as the difference between the sweating threshold and the vasoconstriction threshold. Generally, the interthreshold range is shifted to higher temperatures immediately after surgery under general anesthesia. Thus, thermoregulatory shivering can be exaggerated in patients without hypothermia. The application of patient warming devices and the administration of non-steroidal anti-inflammatory drugs are considered as effective treatments for the prevention of thermoregulatory shivering. Remifentanil is an ultra-short acting agent. Pharmacological effects of remifentanil quickly disappear just after the discontinuing of remifentanil infusion, leading to a kind of opioid withdrawal syndrome resulting in non-thermoregulatory shivering. In addition, postoperative pain shifts the shivering threshold to higher temperatures, resulting in non-thermoregulatory shivering. Thus, opioid transition using fentanyl and/or morphine during anesthetic management is essential for the prevention of non-thermoregulatory shivering. It is also reported that magnesium, ketamine and pethidine have preventive effects on non-thermoregulatory shivering. The mechanism underlying post-operative shivering associated with general anesthesia using remifentanil is very complicated; therefore, we speculate that multimodal approach is required for its prevention.