[Postoperative analgesia after remifentanil]

Providing analgesia is the most important, yet the most difficult aspect of remifentanil anaesthesia, as its effect wears off quickly after infusion is terminated. Longer-acting opioids such as morphine and fentanyl must be given well before patients wake up. Bolus administration of fentanyl approximately 20 minutes before the end of surgery may provide adequate analgesia at emergence and tracheal extubation. However, fentanyl concentration decreases quite rapidly and patients may need repeated dosing until analgesia is attained. Continuous intraoperative low-dose infusion of fentanyl may lead to better analgesia than bolus dosing, because its context-sensitive half-time increases as the infusion lasts longer. Regional anaesthetic technique, such as epidural analgesia and peripheral nerve block can also be used in patients without coagulation abnormalities. Issue of acute tolerance after intraoperative use of remifentanil still awaits further study before final conclusion is reached. Some data suggest that we should not use an unnecessary and high dose of opioid without clear indication. Theoretically, remifentanil infusion can be used in ICU and surgical wards to manage postoperative pain in ventilated as well as spontaneously breathing patients. However, in some susceptible patients, even a very low-rate infusion can still cause significant respiratory depression more than 30 minutes after starting infusion. Pulse oximetry is not sensitive enough to detect early ventilatory depression when patients breathe oxygen-enriched air. Without continuous observation by trained anaesthetists, infusion of remifentanil should not be used casually particularly in non-ventilated patients.