Pulse pressure and end-tidal carbon dioxide for monitoring low native cardiac output during veno-arterial ECLS: a prospective observational study

Abstract

Background: Veno-arterial extracorporeal life support (VA-ECLS) results in cardiopulmonary shunting with reduced native cardiac output (NCO). Low NCO occurrence is common and associated with risk of thromboembolic and pulmonary complications. Practical tools for monitoring NCO during VA-ECLS would therefore be valuable. Pulse pressure (PP) and end-tidal carbon dioxide (EtCO2) are known to be related to cardiac output. We have designed a study to test whether PP and EtCO2 were efficient for the monitoring of NCO during VA-ECLS.

Methods: In this prospective single-center observational study, patients who underwent a VA-ECLS for cardiogenic shock from January 2016 to October 2017 were included, provided low NCO was suspected by a PP < 20 mmHg. NCO was measured with pulmonary artery catheter or echocardiography and compared to PP and EtCO2. The ability of PP and EtCO2 to predict NCO < 1 L/min was evaluated with receiver operating characteristics (ROC) curves.

Results: Among the 106 patients treated with VA-ECLS for cardiogenic shock during the study period, 26 were studied, allowing the collection of 196 study points. PP and EtCO2 relationships with NCO were nonlinear and showed strong correlations for NCO < 2 L/min (r = 0.69 and r = 0.78 respectively). A PP < 15 mmHg and EtCO2 < 14 mmHg had good predictive values for detecting NCO < 1 L/min (area under ROC curve 0.93 [95% CI 0.89-0.96] and 0.97 [95% CI 0.94-0.99] respectively, p = 0.058).

Conclusions: PP and EtCO2 may offer an accurate real-time monitoring of low NCO events during VA-ECLS support. Further studies are needed to show if their utilization may help to implement therapeutic strategies in order to prevent thromboembolic and respiratory complications associated with VA-ECLS, and to improve patients' prognosis.

Trial registration: NCT03323268 , July 12, 2016.

Keywords: Cardiogenic shock; EtCO2; Pulse pressure; VA-ECLS support.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Flowchart. VA-ECLS, veno-arterial extracorporeal life support; PP, pulse pressure; PAC, pulmonary artery catheter; NCO, native cardiac output

Fig. 2

Pulse pressure and EtCO2 relationships with native cardiac output and their determinants. Native cardiac output was assessed with pulmonary artery catheter or echocardiography at the same time as pulse pressure, end-tidal carbon dioxide (EtCO2), arterial carbon dioxide pressure (PaCO2), and heart rate. Figures consist of spline regression representations (cubic spline, P Bruce and Bruce 2017) of the relationships between a pulse pressure and native cardiac output, b pulse pressure and stroke volume, c EtCO2 and native cardiac output, and d PaCO2-EtCO2 gradient and native cardiac output. The variation of model performance according to the X was evaluated through prediction of the error model (p < 0.001, p < 0.001, p = 0.01, and p = 0.3 for figures a, b, c, and d respectively)

Fig. 3

ROC AUCs of pulse pressure and EtCO2 for predicting native cardiac output < 1 L/min. ROC curve for pulse pressure (PP) in red and for end-tidal carbon dioxide (EtCO2) in black. Receiver operating characteristics (ROC) curves quantified by area under the curve (AUC) and 95% CI were obtained from 149 study points because 47 pulse pressure values were missing (patients on concomitant left VAD). p = 0.058 between ROC AUC of PP versus EtCO2 (Delong test)