Correlation of end-tidal carbon dioxide with transthoracic echocardiography derived cardiac output for the assessment of fluid responsiveness: A prospective observational study.

Abstract

Background and aims: Judicious use of intravenous fluid therapy can be lifesaving in the intraoperative period. An assessment of fluid responsiveness is important for it. So, our study aimed to study the correlation between end-tidal carbon dioxide (EtCO₂) and transthoracic echocardiography-derived cardiac output for assessing fluid responsiveness in patients undergoing elective surgery under general anesthesia.

Material and methods: Patients who underwent elective lower abdominal or lower limb surgeries in a supine position under general anesthesia with positive pressure ventilation were included in this study. Cardiac output was calculated using transthoracic echo, and by measuring the diameter of the left ventricular outflow tract (LVOT), velocity time integral of LVOT (LVOT-VTI), and heart rate. Cardiac output (CO), EtCO₂, and hemodynamic and ventilatory parameters were analyzed by the operator before and 1 min after the infusion of 250 mL of normal saline.

Results: EtCO₂ variations showed a weak correlation with the changes in CO induced by a fluid challenge (Spearman's correlation r = 0.3, P = 0.005). When fluid responsiveness (FR) is defined as an increase in CO by > 15%, the AUROC of ∆ EtCO₂ was 0.638 (95% confidence interval [CI], 0.507-0.77). At a cut-off of ≥ 1 mmHg, it predicted FR status (responder vs. non-responder) with a sensitivity of 66% and a specificity of 64%. When percentage variation in EtCO₂ (percent ∆ EtCO₂) was considered, the AUROC was almost similar (0.618) (95% CI, 0.481-0.756), and it was not statistically significant (P = 0.093).

Conclusions: Our study demonstrated a weak positive correlation between volume-induced changes in EtCO₂ and changes in CO in mechanically ventilated patients in the operating room. Variations in EtCO₂ can be used as an adjunct to guide hemodynamic optimization when no COcardiac output monitors are available.