U-shaped association between elapsed time after surgery and the intensity of chronic postsurgical pain following cardiac surgery via thoracotomy: an observational cohort study.

BACKGROUND: Chronic postsurgical pain (CPSP) is defined as chronic pain that develops or increases in intensity after a surgical procedure and persists beyond the healing process, defined as at least 3 months postoperatively. However, the rationale behind this time period is weak. METHODS: This prospective observational study included a total of 238 consecutive patients who underwent mitral valve repair via thoracotomy. A questionnaire consisting of a numerical rating scale (NRS) to assess the severity of postsurgical pain was mailed to each participant more than 3 months after the operation. The outcomes of interest were current pain, peak pain in the last 4 weeks, and average pain in the last 4 weeks, each assessed using the NRS. The nonlinear associations between the elapsed time after surgery and the intensity of CPSP were evaluated. All statistical analyses were performed with a two-sided significance level of 5%. RESULTS: Two-hundred and ten patients (88.2%) answered the questionnaire. There was a significant nonlinear association between the elapsed time after surgery and each NRS response (all, P < 0.05). The lowest adjusted log odds of current pain, peak pain in the past 4 weeks, and average pain in the past 4 weeks were - 1.49, - 1.13, and - 1.26 at 33, 33, and 33 months postoperatively, respectively. CONCLUSIONS: There was a significant U-shaped association between the elapsed time after surgery and intensity of CPSP. The adjusted log odds of each NRS response was lowest at 33 months after cardiac surgery via thoracotomy.