Saturday, January 14, 2012

Chronic Pain Prolongs Postsurgical Pain

Research Update According to recently reported research, patients with chronic pain require special consideration for pain management following any type of surgery. At the least, the postoperative pain is likely to linger longer in these patients, and the pain may be greater if patients were taking opioid analgesics prior to surgery. However, there are still some unanswered questions.

Researchers at the University of Utah School of Medicine, Salt Lake City, followed a convenience sample of 55 patients with preexisting chronic pain for 2 weeks following surgical procedures that were unrelated to their primary chronic pain conditions [Chapman et al. 2011]. Subjects ranged in age from 19 to 85 years (mean 55), 51% were female, and 85% were white. All patients underwent orthopedic surgery, except for one who had a percutaneous nephrolithotomy (kidney stone removal).

Prior to surgery, 30 of the patients with chronic pain had been taking opioid pharmacotherapy for pain management for at least 2 months, while the other 25 had not been taking opioids for pain relief. Starting on postsurgical day 1, on an 11-point numeric rating scale (NRS, 0 to 10), all subjects reported daily on (a) postoperative pain with movement, and (b) pain at rest. Based on the 2 weeks of data recording, researchers were able to calculate composite mean values for the initial level of pain and the rate of pain resolution over time for each group.

Writing in the Journal of Pain, Chapman and colleagues note that earlier research in surgical patients without preexisting chronic pain found that the average initial postoperative level of pain was an NRS score of about 5.5 and the pain resolved by about one-third (0.31) of a point, or pain unit, per day. The subjects with chronic pain, but not previously taking opioids, in this present study had an almost identical initial mean level of pain (5.6 units), but the resolution of pain was much slower at about one-fifth of a pain unit per day (0.20) on average. In contrast, subjects with chronic pain who had been taking opioids started out at a significantly higher postsurgical level of pain (mean 7.68 pain units; P<0.001), which then resolved at about the same rate as for other patients with chronic pain.

In perspective, it appears that patients with chronic pain who undergo surgery generally seem to have the same initial level of postoperative pain as any other surgical patients, but their pain resolves more slowly over time. If patients with chronic pain also have been taking long-term opioid analgesics prior to surgery, they may have markedly higher initial pain levels than other patients with chronic pain, but they resolve their postoperative pain at the same slow rate as the other chronic pain patients.

In both cases, patients with chronic pain are vulnerable to substantially more postoperative pain over time than typical surgical patients. Most importantly, patients with preexisting chronic pain who undergo surgical procedures may require special attention and more aggressive postoperative pain management protocols, and surgical teams should be made aware of this.

COMMENTARY: The researchers note that this is the first study to examine postoperative pain trajectories in patients with chronic pain who use, or do not use, opioids for pain management. At the same time they acknowledge that this was an observational study, using a nonrandom convenience sample, rather than a higher-quality clinical trial, so the conclusions might be somewhat preliminary. A number of limitations should be considered:

  • The researchers discuss opioid-induced hyperalgesia as a possible explanation for patients taking opioid analgesics experiencing higher levels of postoperative pain at the outset. However, while such a theory is consistent with animal studies (eg, rodent models), this sort of hyperalgesia in humans is less well established. Also, in this present study, researchers did not record the length of time patients had been receiving opioids, other than the 2-month minimum to qualify for inclusion, which casts further doubt on whether putative hyperalgesia might have played any role.

    Importantly, the researchers did not assess pain scores prior to surgery and it is possible that those taking opioids simply had more pain going into surgery than the other subjects. The researchers do concede that patients with chronic pain who receive opioids may be those who “hurt more” or are more pain-sensitive for one reason or another, but there also is a question as to whether adequate amounts of opioids had been prescribed for the patients in that group to relieve pain.

  • There was no control group for comparison at the facility where the research was conducted, such as patients without chronic pain undergoing similar surgical procedures. The researchers relied on evidence from prior research to establish “normal” values for postoperative pain and its resolution — ie, postop NRS=5.5; resolution = 0.31 units/day — and this might not have been the case at this particular institution.

  • There was a strong imbalance between groups of body sites where orthopedic surgery was performed, which may or may not have influenced differences in postsurgical pain and its resolution. Patients with chronic pain and taking opioids had more procedures on the back, head and neck, and shoulder; whereas, patients not taking opioids had more procedures on the hip and knee.

It is always disappointing when otherwise good and important research suffers from deficiencies that might challenge the validity of outcomes. Still, it seems reasonable that patients with chronic pain may have special needs for postsurgical pain management, and it should not be assumed that their response to analgesic therapy or the resolution of acute pain over time will be the same as in other patients.

REFERENCE: Chapman CR, Davis J, Donaldson GW, et al. Postoperative Pain Trajectories in Chronic Pain Patients Undergoing Surgery: The Effects of Chronic Opioid Pharmacotherapy on Acute Pain. J Pain. 2011;12(12):1240-1246 [abstract here].