Opioid-induced Hyperalgesia After Remifentanil Infusion

Remifentanil is a rapid-acting opioid which has been widely used in pain treatment during surgery for the last 15 years 1. Remifentanil is rapidly eliminated (minutes) from the body after end of infusion, and this makes it easily manageable compared to other opioids. However, there are both experimental and clinical studies indicating that remifentanil, after end of infusion, triggers increased pain sensation and increased opioid consumption post-operatively. Increased post-operative opioid consumption should be avoided due to the adverse effects of these drugs (nausea/vomiting, pruritus, dizziness, fatigue and reduced respiratory rate). Thus, it's important to investigate relevant strategies to avoid the increased pain sensation (opioid-induced hyperalgesia = hypersensitivity to pain stimuli) after end of infusion of remifentanil after surgery. Several experimental and clinical trials have been conducted in this field. Ketamine has been shown to block this effect, but its adverse effect profile (i.a. hallucinations) makes it not suitable in normal clinical use. In a study of healthy volunteers, it has been demonstrated that parecoxib (a COX-2 selective NSAID) can prevent remifentanil-induced hyperalgesia. Our group has previously shown that a relatively COX-1 selective NSAID (ketorolac) can prevent hyperalgesia in an experimental pain model. This is of interest since NSAIDs are frequently administered as premedication before surgery. There are several disadvantages associated with the use of COX-2 inhibitors, e.g. the risk of myocardial infarction after long-term use (\> 1 year), and potentially reduced bone healing after orthopedic surgery. However, this has not been shown with short-term use (days/week). The disadvantages associated with the use of e.g. ketorolac (a COX-1 inhibitor) are i.a. increased bleeding tendency, which is unfavourable for the surgeon, and increased risk of gastric ulcer. Therefore, it is of interest to investigate other ways of preventing