Use of Regional Opioids In Post-Operative Pain Management

Abstract

The identification of opioid receptors in the substantia gelatinosa of the spinal cord has led to new concepts for treatment of acute and chronic pain. Intense and often prolonged analgesia can be produced by the subarachnoid injection of small doses of opioids, which act directly on opioid receptors in the spinal cord, to interrupt pain pathways. Similarly opioids placed in the epidural space diffuse into the subarachnoid space to gain access to the receptors in the spinal cord.

Intra-thecal opioids are reported to inhibits the release of substance P which is believed to be neurotransmitter for nocioceptive stimuli. Electrophysiological studies have shown that C fiber nocioceptive discharge is more readily blocked than A delta input suggesting that regional opioids relieve dull pain better than sharp pain and wound, therefore, not be expected to block intraoperative pain effectively. However, this method of analgesia has been used successfully in the treatment of postoperative pain. In fact postoperative analgesia is the most common indication for the use of intraspinal opioids.

Analgesia produced with this technique is segmental, profound and long lasting. It is not associated with significant sympathetic or motor blockade and therefore, appears to be superior to that produced by epidural and spinal administration of local anesthetic and intercostal nerve blocks. Intraspinal opioid analgesia has been used to provide postoperative pain relief for thoracic surgery including cardiac surgery, as well as after abdominal and orthopedic procedures. It has been used in different age groups including children and elderly patients with compromised lung function with excellent results. Grossly obese patients were found to ambulate earlier postoperatively when morphine was given to them epidurally: the risks of pulmonary embolism were thus decreased and hospital stay shortened.