Neuronal activation following trauma occurs by direct nociceptor stimulation and the release of chemical mediators from the damaged cells. The latter activate the inflammatory response mediated by local production of prostaglandins, kinins, and other chemicals, resulting in sensitization of nociceptors at the site of injury and primary hyperalgesia. Non-steroidal anti-inflammatory drugs (NSAIDs) are a group of drugs classified as cyclo-oxygenase inhibitors, which inhibit the production of prostaglandins in response to tissue damage. Prostaglandins are involved in the production of secondary hyperalgesia around the injured area and NSAIDs also act here. The peripheral and central effects of NSAIDs result in less activation of nociceptors, less local inflammatory response, perhaps reduced stress response, and less pain.
The clinical properties of NSAIDs include mild to moderate analgesia with a ceiling effect with increasing dose, an anti-inflammatory action, an antipyretic action, reduction in renal blood flow and the glomerular filtration rate, gastric irritation, reduction in platelet adhesiveness, and rare idiosyncratic allergic reactions.
Although less potent than opioids as sole analgesics, many of these drugs reduce opioid requirements in the perioperative period when used as an adjunct to intramuscular, intravenous, or epidural intraspinal opioids, thus yielding improved analgesia, reduced opioid side-effects such as emesis, and faster return of gastrointestinal function (Souter, et,a[ 1994). NSAIDs can be given orally, and some can be given rectally (naproxen, indomethacin) or by injection (ketorolac, tenoxicam, diclofenac). Concerns about renal, gastric, and platelet effects limit the use of these drugs for many critical care patients, although the safety of short-term perioperative use in patients having either minor or major surgery make them attractive. The advantage of preoperative loading rather than intra- or postoperative use is not well established and is probably small. Small increases in perioperative blood loss have been noted with preoperative use of NSAIDs (e.g. during total hip or knee arthroplasty), but initiation of therapy immediately postoperatively eliminates this concern. It is prudent to avoid their use in patients with pre-existing risk factors for bleeding and renal dysfunction, and in the elderly who may be more prone to side-effects. NSAIDs continue to be underutilized in the perioperative period, but are becoming more popular as a component of multimodal analgesia and in patients undergoing ambulatory surgery.
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