Postoperative pain significantly impacts patient recovery. However, postoperative pain management remains suboptimal, perhaps because treatment strategies are based mainly on studies using inflammatory pain models. We used a recently developed mouse model of incisional pain to investigate peripheral and spinal mechanisms contributing to heat hyperalgesia after incision. Behavioral experiments involving TRPV1 KO mice demonstrate that, as previously observed in inflammatory models, TRPV1 is necessary for heat (but not mechanical) hyperalgesia after incision. However, in WT mice, neither the proportion of TRPV1 immunoreactive neurons in the DRG nor the intensity of TRPV1 staining in the sciatic nerve was different from that in controls up to 4 days after incision. This result was corroborated by immunoblot analysis of sciatic nerve in rats subjected to an incision, and is distinct from that following inflammation of the rat hind paw, a situation in which TRPV1 expression levels in sciatic nerve increases. In the absence of heat exposure, spinal c-Fos staining was similar between incised TRPV1 KO and WT mice. However, differences in c-Fos staining between heat exposed TRPV1 KO and WT mice after incision suggest that the incision-mediated enhancement of heat-evoked signaling to the spinal cord involves a TRPV1-dependent mechanism. Finally, heat hyperalgesia after incision was reversed by antagonism of spinal non-NMDA receptors, unlike inflammatory hyperalgesia, which is mediated via NMDA receptors . Thus, TRPV1 is important for the generation of thermal hyperalgesia after incision. Our observations suggest that all experimental pain models may not be equally appropriate to guide the development of postoperative pain therapies.

Background: The aim of this study was to determine simple risk factors for severe pain intensity (≥7 points on a numeric rating scale [NRS]), to analyse their relation to other patient-reported outcome measures and to develop a simple prediction model. Methods: We used data from 50,005 patients from the PAIN-OUT project. Within a first data set (n = 33,667), relevant risk factors were identified by logistic binary regression analysis, assessed for additional patient-reported outcome measures beyond pain intensity and summed up for developing a simple risk score. Finally, sum of factors was plotted against postoperative pain outcomes within a validation data set (n = 16,338). Results: Odds ratios (OR) for the following risk factors were identified: younger age (90 minutes, OR: 1.308), preoperative opioid intake (OR: 1.250), feeling anxious (OR: 1.239) and feeling helpless due to pain (OR: 1.198), and the country of the recruiting centre (OR: 1.919). Patients with ≥3 risk factors had more severe pain intensity scores, spent a longer time in severe pain, and wished to have received more pain treatment (P < 0.001). A simple risk score was created with 4 risk factors showing a moderate prediction level. Conclusions: Patients with ≥3 risk factors are at higher risk for poor postoperative acute pain outcome after surgery. Future studies using this score might show that preventive strategies might decrease pain intensity, pain-related postoperative dysfunction, and the development of chronic pain.

Postoperative pain management is still insufficient, leading to major deficits, including patient suffering, impaired surgical recovery, long-term opioid intake, and postsurgical chronic pain. Yet, identifying the best treatment options refers to a heterogeneous outcome assessment in clinical trials, not always reflecting relevant pain-related aspects after surgery and therefore hamper evidence synthesis. Establishing a core outcome set for perioperative pain management of acute pain after surgery may overcome such limitations. An international, stepwise consensus process on outcome domains (“what to measure”) for pain management after surgery, eg, after total knee arthroplasty, sternotomy, breast surgery, and surgery related to endometriosis, was performed. The process, guided by a steering committee, involved 9 international stakeholder groups and patient representatives. The face-to-face meeting was prepared by systematic literature searches identifying common outcome domains for each of the 4 surgical procedures and included breakout group sessions, world-café formats, plenary panel discussions, and final voting. The panel finally suggested an overall core outcome set for perioperative pain management with 5 core outcome domains: physical function (for a condition-specific measurement), pain intensity at rest, pain intensity during activity, adverse events, and self-efficacy. Innovative aspects of this work were inclusion of the psychological domain self-efficacy, as well as the specific assessment of pain intensity during activity and physical function recommended to be assessed in a condition-specific manner. The IMI-PROMPT core outcome set seeks to improve assessing efficacy and effectiveness of perioperative pain management in any clinical and observational studies as well as in clinical practice.