Evaluation of end-tidal carbon dioxide as a marker of fluid responsiveness in mechanically ventilated patients with shock: a prospective study in a tertiary care center in India

Shock management in intensive care unit (ICU) patients requires accurate assessment of fluid responsiveness to optimize outcomes. Dynamic indices, such as passive leg raising (PLR), are often underutilized due to invasive or complex techniques. Our aim was to evaluate change in end-tidal carbon dioxide (EtCO₂) during PLR as a non-invasive dynamic index of fluid responsiveness in mechanically ventilated ICU patients with shock. This was a prospective, observational cohort study conducted in a respiratory ICU at a tertiary care center in New Delhi, India. The study recruited adult patients on mechanical ventilation with shock between November 2022 and April 2024. After screening 340 ICU admissions during the recruitment period for inclusions and exclusions, a total of 90 adult patients on mechanical ventilation with shock were enrolled in the study. Measurements of EtCO₂ via mainstream capnography and cardiac output (CO) with transthoracic echocardiography (TTE) were done pre- and post-PLR. Fluid responsiveness was defined as a ≥10% increase in CO measured via TTE following PLR. Simultaneously, EtCO₂ was measured, with a ≥5% increase considered predictive of fluid responsiveness. Sensitivity, specificity, and the area under the receiver operating characteristic curve (AUROC) were calculated for EtCO₂. The study found a sensitivity of 86.8% and specificity of 88.5% for a ≥5% increase in EtCO₂, with an AUROC of 0.951, indicating high diagnostic accuracy. A significant correlation was observed between EtCO₂ changes and fluid responsiveness, validating EtCO₂ as a reliable predictor comparable to TTE. To conclude, EtCO₂ monitoring during PLR is a practical, non-invasive tool for assessing fluid responsiveness in ICU patients with shock. This method is suitable for bedside application, particularly in resource-limited settings, and supports informed fluid management decisions. Further multicenter studies are recommended to confirm its broader applicability.