“[I]n reality patients are spread along a spectrum of severity […], the use of continuous outcomes increases statistical power of a study, allowing for better detection of more subtle clinical effects.”
Boko et al. found that CPSP occurred in 12% of patients in their same-day surgery cohort, and 6.7% reported opioid use at 90 days after surgery. The great majority (93.1%) of patients with CPSP did not report preoperative pain at the surgical site and thereby were considered new-onset CPSP. The authors also found that active smoking, certain surgical subtypes (orthopedic, plastic, breast, and vascular), and ethnicities (Hispanic/Latino and First Nations/Native) were associated with CPSP, highlighting the importance of prospectively identifying those at risk for the development of CPSP.
We commend the authors for the importance of this work, made all the more significant and broadly applicable due to their methodologic rigor in conducting a large-scale prospective study across multiple sites and surgical types. Comparing associations between studies of CPSP can be challenging due to the varying outcome measures used. Our previous systematic review of genetic factors of postsurgical pain revealed discrepant outcomes in time frame, pain outcome (analgesic use vs. patient reported pain score), and pain reporting modality. Boko et al. used a well validated outcome (the Brief Pain Inventory) and standardized analgesic usage metrics across participating centers, significantly minimizing variability and strengthening the conclusions.
Consistent outcome definitions for CPSP are essential to both ensure accuracy and to enable comparisons across studies. The International Association for the Study of Pain defines CPSP as pain that develops or intensifies after a surgical procedure persisting for at least 3 months after surgery. However, cutoffs of numeric pain rating scales of greater than 0, greater than or equal to 3, or greater than or equal to 4 have been used to segregate those with and without CPSP, varying the included population and specificity of the measure. Clinically relevant changes in pain intensity are often described as greater than or equal to 2 points on an 11-point scale (from 0 to 10), although that is mainly intended to evaluate treatment efficacy in trials. In the current study, two definitions of CPSP were used (CPSP as an increase in Brief Pain Inventory score greater than or equal to 1 over baseline, or moderate to severe CPSP as a Brief Pain Inventory score greater than or equal to 4 out of 10), and there are unsurprisingly differences in the findings between each classification. This underscores the need for consistent outcome measures and consensus definitions for future studies, including reporting of multiple outcomes. Further, it is important to stress that binary and/or dichotomized measures (such as CPSP, opioid use, or presence of anxiety in the current study) separate patients into groups with an arguably arbitrary delineation between groups. However, in reality patients are spread along a spectrum of severity, and we therefore encourage the use of measures with continuous outcomes. Furthermore, the use of continuous outcomes increases the statistical power of a study, allowing for better detection of more subtle clinical effects.
The current study by its design, as part of the larger VALIANCE study, is limited in its ability to identify associations with CPSP for biopsychosocial factors such as pain quality, disability, function, fatigue, sleep, activity levels, and social support. Assessment of pain was not a primary or secondary outcome measure of the VALIANCE study, although it is the primary outcome of this substudy; this leads to the recommendation that nonpain studies include at least basic pain measures in their secondary outcomes a priori. Biopsychosocial modulators of pain have long been identified, and their effects on pain outcomes are well established.
There is also a need for future pain-focused studies to distinguish between surgical site pain and general body pain in baseline assessments and to record data on acute postsurgical pain so as to understand its impact on overall pain trajectory. Moreover, widespread body pain indicative of nociplastic pain is easily assessed via pain body maps and is valuable for any patient at risk of chronic pain. The currently underway Acute to Chronic Pain Signatures (A2CPS, www.a2cps.org) program, the largest ever National Institutes of Health–funded (Bethesda, Maryland) study of postsurgical pain, is evaluating patient-reported outcomes, multiple -omics measures, quantitative sensory testing, functional measures, and neuroimaging for signals associated with acute and chronic postsurgical pain. Additionally, the longstanding work of the ACTTION and IMMPACT clinical pain consensus groups have provided guidelines for the classification of chronic pain conditions and appropriate measurements of patient-focused determinates of pain outcomes. The Early Phase Pain Investigation Clinical Network (EPPIC-Net), as part of the National Institutes of Health HEAL (Helping to End Addiction Long-term) Initiative, is another clinical trial network providing free expertise in design, management, and analysis for investigations into pain and pain therapies. We encourage investigators to try to align measures to enable future comparisons, systematic reviews, and meta-analyses.
We applaud Boko et al. for their important work and the effort required to undertake it. Despite the limitations, identifying a high rate of CPSP in same-day surgery should spur further research in these cohorts and comparisons to the more classically described CPSP surgical conditions. Future research should incorporate comprehensive psychologic and pain assessment tools, broaden participant demographics, and utilize definitions of CPSP consistent with emerging consensus from pain research consortiums. The role of multisite studies like this one is crucial and represents a significant investment in understanding and managing postsurgical pain effectively.
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