Detecting if change in end-tidal carbon dioxide signifies change in cardiac output for the prediction of fluid responsiveness in patients undergoing major abdominal oncosurgery: An observational study.

BACKGROUND AND AIMS: Changes in end-tidal carbon dioxide (ΔETCO2) have been proposed as a predictor of fluid responsiveness, but the available evidence remains inconsistent. We evaluated the ability of ΔETCO2 to predict a ≥10% increase in cardiac index (ΔCI) following administration of a 4 mL/kg crystalloid bolus in patients undergoing major abdominal surgery. METHODS: We conducted a prospective study in 22 adults undergoing major abdominal surgery between April 2022 and January 2023. Cardiac output and stroke volume were monitored using the FloTrac™ system with a Vigileo or EV1000 monitor. Patients were mechanically ventilated with a tidal volume of 8 mL/kg predicted body weight and a respiratory rate of 12-16 breaths/min. An intravenous bolus of Ringer's lactate (4 mL/kg actual body weight over 10 minutes) was administered when haemodynamic parameters suggested hypovolaemia. Patients with a ΔCI ≥10% were classified as fluid responders, with ΔCI serving as the reference standard. ΔETCO2 was evaluated against changes in stroke volume index (ΔSVI) and compared with pulse pressure variation (PPV) and stroke volume variation (SVV). Diagnostic performance was assessed using the area under the receiver operating characteristic (AUROC) curve. RESULTS: ΔETCO2 moderately predicted fluid responsiveness, with an AUROC of 0.823 [95% confidence interval (CI): 0.688-0.955] at a threshold of 1.5 mmHg (Youden index: 0.588, P < 0.001). It outperformed pre-bolus PPV and SVV, which had AUROC values of 0.563 (95% CI: 0.344-0.782; threshold 16.5%; Youden index: 0.242; P = 0.554) and 0.427 (95% CI: 0.209-0.644; threshold 12.5%; Youden index: 0.050; P = 0.508), respectively. CONCLUSION: ΔETCO2 may be a useful marker of fluid responsiveness after a fluid challenge.