Correlation of Cardiac Output Determined by Echocardiography and Indirect Calorimetry in Critically Ill Patients in Cardiogenic Shock on Extracorporeal Circulatory Life Support

Patients in perioperative cardiogenic shock often require hemodynamic support. If supportive therapy is not sufficient, the implementation of mechanical extracorporeal life support (ECLS) represents a rescue therapy. This procedure enables a "bridge-to-recovery" strategy, i.e. bridging the cardiogenic shock until the patient recovers. The ECLS uses a pump to support the circulation by drawing in blood through a venous cannula, oxygenating it extracorporeally and reinfusing it into the body under pressure through an arterial cannula. In addition to this share of cardiac output (CO) provided by the ECLS, the beating heart can also contribute part of the CO in cardiogenic shock. Following, blood flow generated by the ECLS system will be referred to as ECLS CO and blood flow generated by the heart as cardiac CO. In patients without ECLS, the total CO can be estimated and determined non-invasively using transthoracic echocardiography. In patients with ECLS, the cardiac CO is also determined by echocardiography in everyday clinical practice, even if the validity of this procedure in patients receiving ECLS therapy has not been conclusively established. Indirect calorimetry, which is routinely used to determine energy expenditure in critically ill patients, could be another method of estimating cardiac CO. However, the extent to which the results of indirect calorimetry and ultrasound-based cardiac CO correlate is unclear and has not yet been investigated. However, a correlation of sonographic and calorimetric findings would be helpful in everyday clinical practice, as in some patients it is not possible to determine the cardiac CO by sonography for technical reasons.

The daily measurement of resting energy expenditure (REE), oxygen consumption (VO2) and CO2 production (VCO2) is carried out using indirect calorimetry in patients with veno-arterial ECLS support to bridge cardiogenic shock after cardiac surgery. In these patients, the cardiac CO is regularly determined daily using transthoracic echocardiography. The measurements are taken daily until the second day after cessation of ECLS therapy. The parameters obtained on the day of admission to the intensive care unit and directly before ECLS explantation will then be correlated with each other and examined for a possible correlation. Further data obtained will be examined as part of exploratory evaluations.