State of the art in Acute Pain Medicine
ACUTE PAIN MANAGEMENT – NEW EVIDENCE FOR DRUGS AND TECHNIQUES
SA Schug
University of Western Australia, Perth, WA,
The review of the current literature to develop the document ‘Acute Pain Management:Scientific Evidence’, which has been introduced by the previous speaker, revealed a large amount of new information supporting the use of certain drugs and techniques to relieve acute pain:
Among the techniques supported is the concept of multimodal analgesia, i.e. the use of multiple analgesic compounds with different mechanism of action. There is now very good literature supporting this approach, which confirms its beneficial effects on reducing doses needed and adverse effects experienced, while improving analgesia. Useful components of multimodal analgesia are paracetamol, NSAIDs and coxibs, but also possibly gabapentin and in specific situations ketamine. Such situations are severe pain poorly responsive to opioids and/or opioid tolerance.
Ketamine as an NMDA receptor antagonist is also useful to provide preventive analgesia, a concept defined as analgesic interventions, which have an effect on postoperative pain and/or analgesic consumption that exceeds the expected duration of action of the drug. This new concept has more useful clinical implications than the continuously debated term preemptive analgesia, which was limited to the timing of a single analgesic intervention in most trials.
With regard to non-opioid analgesics, the benefits of paracetamol have been confirmed as well as the usefulness of combining it with NSAIDs or coxibs. NSAIDs and coxibs are equally effective for treatment of acute pain, but short-term use of coxibs offer advantages with regard to haemostasis, bronchospasm, gastric ulceration and bone healing. Coxibs are contraindicated after CABG, but do not increase cardiovascular morbidity or mortality in other types of surgery. Both groups, NSAIDs and coxibs, have similar adverse effects on the kidneys. However, these occur rarely with careful patient selection and monitoring; risk factors are pre-existing renal impairment, hypovolaemia, hypotension and use of other nephrotoxic agents and ACE inhibitors.
With regard to opioids, the poor efficacy and potential risks of dextropropoxyphene have been identified and its use is discouraged; its registration in the UK is currently phased out. Opioid rotation in case of inefficacy or adverse effects is supported and a dose-relationship for clinically meaningful adverse effects of opioids is established. Tramadol has a lower risk of respiratory depression and impairs gastrointestinal motor function less than other opioids at equianalgesic doses.
In addition, the effectiveness of tramadol in neuropathic pain has been confirmed by a Cochrane review, The preferable technique for the parenteral administration of opioids remains PCA without a background infusion and there is no evidence for one opioid being superior to others in this setting. Transferring the concept of PCA to other routes of administration maintains its beneficial effects (subcutaneous, intranasal, transdermal, epidural).
The use of co-analgesics such as anti-depressants, anti-convulsants and membrane stabilizers in acute neuropathic pain is nearly exclusively based on data on their effects in chronic pain states. Only for systemic lignocaine, there is supportive literature in acute pain treatment. Calcitonin is effective to treat pain of osteoporotic vertebral fractures and phantom limb pain.
Of the long-acting local anaesthetics, the enantiomer specific ones (i.e. ropivacaine and levobupivacaine) are offering significant safety advantages. For epidural administration, combinations of local anaesthetics with opioids are supported. The addition of other adjuvants such as clonidine and neostigmine can improve analgesia, but with an increase of adverse effects in most studies. However, the addition of adrenaline results in clinically useful improvements of postoperative epidural analgesia. There is now Level I evidence for the beneficial effects of epidural analgesia on postoperative outcome with regard to better analgesia (with any drug via any catheter location) and for thoracic epidural analgesia using local anaesthetics with regard to reduced pulmonary complications and myocardial infarctions and improved bowel recovery without increased risk of anastomotic leakage. There is also increasing evidence for the beneficial role of continuous peripheral nerve blocks in the provision of postoperative analgesia.
Non-pharmacological techniques such as psychological interventions, TENS and acupuncture are effective in certain acute pain settings and might currently be underutilized.
Overall, there is now a vast amount of scientific data available to guide the management of acute pain. However, the challenge remains to implement these results in the daily clinical routine, in particular in view of the financial, time and personnel constraints of our health care system. The even greater challenge will be, to utilise the pain relief achieved to improve and speed up patient recovery in a model of postoperative rehabilitation.
Australian and New Zealand College of Anaesthetists, Faculty of Pain Medicine. Acute pain management: scientific evidence. 2nd ed. Melbourne: Australian and New Zealand College of Anaesthetists; 2005.
Accessible at: http://www.anzca.edu.au/publications/acutepain.htm and
http://www7.health.gov.au/nhmrc/publications/synopses/cp104syn.htm
Time of Presentation
Saturday 13 May 2006 - 1030-1200
