Managing Postoperative Pain: What Do We Know?

February 29, 2012

Given that pain following surgery is predictable, one might assume we know a lot about optimal analgesia and management. A meta-analysis of Cochrane Reviews, however, reveals that we still have a lot to learn. Read more, here.

Of all the forms of pain, postoperative pain is one of the most ubiquitous. Rarely does someone undergo any form of surgery without suffering pain, ranging from relatively mild to overwhelmingly severe. Based on this, it would be easy to assume that we have a large body of information about optimal medications for managing this problem.

However, a new review article questions how much we really do know about the best way to treat patients who are experiencing postoperative pain.1 The authors performed a meta-analysis of 35 Cochrane Reviews (350 studies and more than 45,000 adult patients) that examined the efficacy of oral analgesic medications for controlling postoperative pain. Reliable results were found for 46 individual drugs or drug combinations.

Results
Of the 46 agents examined, 40 were NSAIDs or acetaminophen; 4 were combinations of oxycodone or codeine and acetaminophen; 1 was dextropropoxyphene plus acetaminophen (Darvocet; no longer available in the US); and 1 was codeine monotherapy.

The most effective drugs and dosages, based on the number of patients needed to treat in order to achieve 50% maximum pain relief over 4 to 6 hours, were:
• Etoricoxib, 180/240 mg and 120 mg (this selective COX-2 inhibitor is not
available in the US)
• Oxycodone, 10 mg plus acetaminophen 1000 mg
• Difunisal, 1000 mg
• Ketoprofen, 25 mg
• Codeine, 60 mg plus acetaminophen 800/1000 mg

Drugs at the bottom of the list were:
• Acetaminophen, 600/650 mg
• Codeine, 60 mg

In general-probably not too surprisingly-the authors found that medications with a longer duration of action tended to provide better pain relief. Many of the medications provided a similar amount of analgesia. Because patients can vary significantly in their response to medications, if one agent or one class of agents doesn’t work it makes sense to keep trying different drugs and/or combinations until you find one that works best for that individual.

Limitations of this review
There are important caveats that limit the usefulness of this meta-analysis and of the reviews upon which it is based:
• The studies only examined the efficacy of a single dose of oral analgesics.
• Of the 46 drugs and dosages 45 were studied for dental pain while only 14 were studied for other forms of postsurgical pain such as episiotomy, orthopedic procedures, or abdominal surgery. While pain from dental procedures can be severe, it is often quite different from other forms of postsurgical pain. One difference is that postoperative dental pain is often relatively short lived, and because oral surgery is restricted to a well-confined area of the body, it does not usually affect the function of other systems. Bowel function, for example, is rarely a concern after dental surgery but poses significant issues after most types of major surgery. Furthermore, there is often some delay before patients can take oral medications following major surgery elsewhere in the body. Because of these differences, it is usually far easier to study dental pain. This fact, in turn, is probably the reason that most of these addressed this form of pain and relatively few addressed pain related to more invasive procedures.

It is not surprising that most drugs examined in this review were NSAIDs, as dental surgery pain is primarily limited to bone. In general, this type of pain responds best to this class of drugs.
•There are many other analgesics, including some commonly used for postoperative pain, for which there were no studies that offered reliable efficacy data, so these drugs were not included in the review

Conclusions
Despite these limitations, there are several interesting findings:
• Although many health care professionals believe that opioids are the most effective analgesics, clearly other drugs, depending on the form of pain, can be equally effective and even provide more relief.
• Combination therapy with codeine 60 mg plus acetaminophen 800/1000 mg performed relatively well, but monotherapy with codeine 60 mg or acetaminophen 1000 mg offered much less relief. Perhaps the better relief provided by the combination drug is related to synergy (one agent heightening the effect of the other) or because the drugs working through different physiologic mechanisms, but this remains unclear. It does not appear that any reliable studies were found that tested combinations of an opioid and an NSAID, so we don't know how this would have compared with the opioid-acetaminophen combination.
• The finding that oxycodone 10 mg plus acetaminophen 1000 mg and codeine 60 mg plus acetaminophen 800/1000 mg provided better pain relief than the same doses of the opioids combined with lower doses of acetaminophen shows that analgesia provided by acetaminophen should not be discounted.

Overall, this meta-analysis demonstrates the limits to our knowledge of how to best medically manage postoperative pain. Perhaps the best contribution of this review is to call attention to these limits and to highlight the need for further research.

Reference
Moore RA, Derry S, McQuay HJ, et al. Single dose oral analgesics for acute postoperative pain in adults. Cochrane Library. September 7, 2011. Available at http://summaries.cochrane.org/CD008659/single-dose-oral-analgesics-for-acute-postoperative-pain-in-adults.