Protocol development for high-resolution transcutaneous CO₂ monitoring in ultra-early detection of free flap compromise.

[BACKGROUND] Vascular compromise is a serious complication in free-flap surgery for traumatic reconstruction or fracture-related infections, often leading to partial or total flap loss if not detected promptly. We evaluated transcutaneous partial pressure of carbon dioxide (TcPCO₂) real-time monitoring as an objective, non-invasive method for ultra-early detection of vascular compromise in free flap reconstruction.

[METHODS] This sequential cohort study consisted of a retrospective development phase and a prospective validation phase. An abnormality was defined as a rise of >10 mmHg from the baseline TcPCO₂ value, with re-exploration performed if the elevation persisted after recalibration. High-resolution (1-s interval) TcPCO₂ data were analyzed to assess diagnostic accuracy and concordance with arterial partial pressure of carbon dioxide (PaCO₂).

[RESULTS] In pilot studies, TcPCO₂ increased within 20-100 s of induced ischemia and correlated strongly with PaCO₂ (r = 0.708, p < 0.001). Among 81 clinical free flap cases (50 retrospective, 31 prospective), TcPCO₂ monitoring detected all seven episodes of vascular compromise with 100% sensitivity and specificity, and no false positives. All the compromised flaps were successfully salvaged. Compared with conventional clinical assessment, TcPCO₂ monitoring provided earlier recognition of perfusion disturbances.

[CONCLUSION] TcPCO₂ monitoring is a non-invasive, objective, and reproducible tool for ultra-early detection of vascular compromise in free flap surgery. Its implementation enables timely re-exploration, reduces reliance on subjective bedside assessments, and may significantly improve flap salvage outcomes.