Figure 1.

Representation of the different components generating cardiac output. In addition to the measurement of left ventricular stroke volume based on the Doppler method most frequently applied at the level of the outflow tract, critical care echocardiography has the major advantage over “blind” continuous monitoring methods such as transpulmonary thermodilution to: (I) measure myocardial fiber shortening (e.g., ejection fraction); (II) assess preload responsiveness (e.g., respiratory variations of maximal aortic Doppler velocity, superior and inferior vena cava) and indirectly evaluate myocardial contractility (i.e., myocardial wall thickening); (III) take into account potential left ventricular remodeling with associated changes in its cavity size (e.g., underlying cardiomyopathy). Left ventricular end-diastolic volume depends on preload, compliance, heart rate, potential remodeling and right-left ventricular interactions (e.g., acute right ventricular dilatation). Left ventricular end-systolic volume depends on contractility, afterload and potential remodeling. All these factors are best depicted by echocardiography. ΔVmaxAo, respiratory variation (white bars depict maximal and minimal measurements in the respiratory cycle) of maximal aortic Doppler velocity; ΔSVC, respiratory variation of superior vena cava (transesophageal echocardiography); ΔIVC, respiratory variations of inferior vena cava; LVOT Æ, left ventricular outflow tract diameter allowing to calculate the cross-sectional area of the orifice (circle); LVOT VTI, velocity-time integral measured at the very same location within the left ventricular outflow tract (white line; arrowhead shows airway pressure tracing with the beginning of mechanical insufflation); DCM, dilated cardiomyopathy; HCM, hypertrophic cardiomyopathy; LVSV, left ventricular stroke volume; EF, ejection fraction; EDD, end-diastolic diameter (double-headed arrows).