Preoperative cardiopulmonary variability assessment for predicting postoperative adverse events following thoracic surgery: A systematic review

Objectives: Postoperative adverse events (AEs) remain a major source of morbidity and mortality following thoracic surgery. Current preoperative risk assessment tools have limited ability to predict individual postoperative complications. Cardiopulmonary variability assessment (CPVA), including heart rate variability (HRV) and respiratory rate variability (RRV), has emerged as a potential biomarker of autonomic function and physiologic reserve. This systematic review evaluated the role of preoperative CPVA in predicting postoperative AEs following thoracic surgery. Methods: A systematic review was conducted according to PRISMA 2020 guidelines. MEDLINE and Embase were searched from inception to identify studies evaluating preoperative HRV and/or RRV as predictors of postoperative AEs in adults undergoing thoracic surgery. Eligible study designs included randomized controlled trials, cohort studies, case-control studies, and diagnostic accuracy studies. Study characteristics, CPVA methodology, comparator assessments, postoperative outcomes, and risk of bias were extracted and evaluated using the Newcastle–Ottawa Scale and QUADAS-2. Results: Five cohort studies comprising 693 patients met the inclusion criteria. Four studies evaluated pulmonary resection for non-small cell lung cancer and one evaluated esophagectomy. Three studies assessed HRV directly, while two evaluated functional measures of cardiopulmonary reserve. Reduced preoperative HRV, particularly lower root mean square of successive differences (RMSSD) and high-frequency power (HFP), was associated with postoperative pneumonia, atrial fibrillation, and delirium. Lower RMSSD (OR 0.812, 95% CI 0.720–0.912) and HFP (OR 0.990, 95% CI 0.983–0.996) independently predicted postoperative pneumonia, with good discrimination (AUC 0.867). Risk of bias was low to moderate. Conclusions: Preoperative CPVA, particularly HRV, is a promising non-invasive biomarker for predicting postoperative AEs following thoracic surgery. Reduced HRV was consistently associated with pulmonary, cardiac, and neurologic complications. Larger prospective multicentre studies using standardized acquisition and analysis protocols are required to establish the incremental value of CPVA beyond current preoperative risk assessment tools.