Assessing the Utility of End-Tidal Carbon Dioxide as a Marker for Fluid Responsiveness in Cardiogenic Shock

Background Preventing end-organ failure in patients with shock requires rapid and easily accessible measurements of fluid responsiveness. Unlike septic shock, not all patients in cardiogenic shock are preload responsive. We conducted this study to determine the discriminant power of changes in end-tidal carbon dioxide (ETCO(2)), systolic blood pressure (SBP), inferior vena cava (IVC) collapsibility index (IVC-CI), and venous to arterial carbon dioxide (Pv-aCO(2)) gap after a fluid challenge and compared it to increases in cardiac output. Methodology In a prospective, quasi-experimental design, mechanically ventilated patients in cardiogenic shock were assessed for fluid responsiveness by comparing improvement in cardiac output (velocity time integral) with changes in ETCO(2), heart rate, SBP, Pv-aCO(2) gap, IVC-CI after a fluid challenge (a crystalloid bolus or passive leg raise). Results Out of 60 patients, with mean age 61.3 ± 14.8 years, mean acute physiology and chronic health evaluation (APACHE) score ­14.82 ± 7.49, and median ejection fraction (EF) 25% (25-35), 36.7% (22) had non ST-segment elevation myocardial infarction (NSTEMI) and 60% (36) were ST-segment elevation myocardial infarction (STEMI). ETCO(2) was the best predictor of fluid responsiveness; area under the curve (AUC) 0.705 (95% confidence interval (CI) 0.57-0.83), p=0.007, followed by reduction in Pv-aCO(2) gap; AUC 0.598 (95% CI; 0.45-0.74), p= 0.202. Changes in SBP, mean arterial pressure (MAP), IVC-CI weren’t significant; 0.431 (p=0.367), 0.437 (p=0.410), 0.569 (p=0.367) respectively. The discriminant value identified for ETCO(2) was more than equal to 2 mmHg, with sensitivity 58.6%, specificity 80.7%, positive predictive value 73.9% [95% CI; 56.5% to 86.1%], negative predictive value 69.7% [95% CI; 56.7% to 76.9%]. Conclusions Change in ETCO(2) is a useful bedside test to predict fluid responsiveness in cardiogenic shock.