CROPS Study: Chronification of Post-Surgical Pain and Risk Assessment

Chronic post-surgical pain (CPSP) is a common and clinically significant complication following cardiac surgery and is associated with impaired functional recovery, reduced quality of life, prolonged opioid exposure, and increased healthcare utilization. Despite substantial advances in perioperative care, a considerable proportion of patients continue to experience persistent pain for months after surgery. The pathophysiology of CPSP is multifactorial and involves complex interactions among surgical tissue injury, peripheral and central sensitization, neuroinflammatory activation, altered pain modulation pathways, and psychosocial vulnerability factors.

Optimization of perioperative analgesia has been proposed as a strategy to reduce nociceptive input, attenuate perioperative stress responses, and potentially decrease the risk of pain chronification. Regional anesthesia techniques, particularly chest wall plane blocks, have demonstrated beneficial effects on acute postoperative pain control and opioid-sparing outcomes in cardiac surgery. However, their influence on long-term pain outcomes and the development of CPSP remains incompletely understood.

The CROPS study (Chronification of Post-Surgical Pain and Risk Assessment) is a prospective multicenter randomized controlled trial designed to evaluate the impact of perioperative analgesic strategies on postoperative recovery and chronic pain development in adult patients undergoing cardiac surgery. Participants will be randomized to receive either standard multimodal opioid-based perioperative analgesia or regional anesthesia-based perioperative analgesia incorporating chest wall plane block techniques, including erector spinae plane block, paravertebral block, or PECS block, according to institutional practice.

The study will compare postoperative pain intensity, opioid consumption, postoperative recovery parameters, postoperative complications, health-related quality of life, and the incidence of chronic post-surgical pain at 3 months after surgery. Particular emphasis will be placed on evaluating whether regional anesthesia-based analgesic strategies reduce perioperative opioid exposure and improve both short-term and long-term patient-centered outcomes.

In parallel, the study aims to validate a novel questionnaire-based pain chronification risk assessment tool intended to identify patients at increased risk of developing CPSP. Predictive performance of the questionnaire will be evaluated using receiver operating characteristic (ROC) analysis, including assessment of area under the curve (AUC), sensitivity, specificity, discrimination, and calibration performance.

The primary outcome measures are the incidence of chronic post-surgical pain at 3 months following surgery and the predictive accuracy of the pain chronification risk assessment questionnaire. Secondary outcomes include postoperative pain intensity, perioperative opioid consumption expressed as morphine milligram equivalents, postoperative nausea and vomiting, postoperative recovery parameters, respiratory complications, duration of mechanical ventilation, intensive care unit length of stay, hospital length of stay, postoperative complications, in-hospital mortality, and changes in quality-of-life and pain-related functional outcome measures.

The study is conducted as an investigator-initiated multicenter academic collaboration between the East Slovakia Institute of Cardiovascular Diseases, Košice, Slovakia, and Uppsala University Hospital, Uppsala, Sweden.

Inclusion criteria

• Age ≥18 years
• Elective cardiac surgery requiring median sternotomy, including:
• coronary artery bypass grafting (CABG)
• aortic valve replacement or repair
• mitral valve replacement or repair
• ascending aorta surgery
• Ability to understand study information
• Ability to provide written informed consent
• Expected postoperative hospital stay longer than 3 days
• Availability for follow-up at 1 week and 3 months after surgery

Exclusion criteria

• Emergency surgery
• Cognitive impairment preventing study participation
• Serious psychiatric illness interfering with study participation
• Language barrier preventing questionnaire completion
• Participation in another interventional study affecting pain outcomes
• Reoperation for postoperative bleeding
• Severe chronic renal failure
• Allergy or contraindication to study medication or regional anesthesia techniques
• Pregnancy or breastfeeding
• Chronic opioid therapy exceeding 60 mg morphine equivalents daily
• Extensive emergency aortic surgery (e.g., Thoraflex implantation for acute aortic dissection)