Cardiac output (CO) monitoring is a valuable tool for the diagnosis and management of critically ill patients. In the critical care setting, few studies have evaluated the level of agreement between CO estimated by transthoracic echocardiography (CO-TTE) and that measured by the reference method, pulmonary artery catheter (CO-PAC). The objective of the present study was to evaluate the precision and accuracy of CO-TTE relative to CO-PAC and the ability of transthoracic echocardiography to track variations in CO, in critically ill mechanically ventilated patients. Thirty-eight mechanically ventilated patients fitted with a PAC were included in a prospective observational study performed in a 16-bed university hospital ICU. CO-PAC was measured via intermittent thermodilution. Simultaneously, a second investigator used standard-view TTE to estimate CO-TTE as the product of stroke volume and the heart rate obtained during the measurement of the subaortic velocity time integral. Sixty-four pairs of CO-PAC and CO-TTE measurements were compared. The two measurements were significantly correlated (r = 0.95; p < 0.0001). The median bias was 0.2 L/min, the limits of agreement (LOAs) were –1.3 and 1.8 L/min, and the percentage error was 25%. The precision was 8% for CO-PAC and 9% for CO-TTE. Twenty-six pairs of ΔCO measurements were compared. There was a significant correlation between ΔCO-PAC and ΔCO-TTE (r = 0.92; p < 0.0001). The median bias was –0.1 L/min and the LOAs were –1.3 and +1.2 L/min. With a 15% exclusion zone, the four-quadrant plot had a concordance rate of 94%. With a 0.5 L/min exclusion zone, the polar plot had a mean polar angle of 1.0° and a percentage error LOAs of –26.8 to 28.8°. The concordance rate was 100% between 30 and –30°. When using CO-TTE to detect an increase in ΔCO-PAC of more than 10%, the area under the receiving operating characteristic curve (95% CI) was 0.82 (0.62–0.94) (p < 0.001). A ΔCO-TTE of more than 8% yielded a sensitivity of 88% and specificity of 66% for detecting a ΔCO-PAC of more than 10%. In critically ill mechanically ventilated patients, CO-TTE is an accurate and precise method for estimating CO. Furthermore, CO-TTE can accurately track variations in CO.

In critically ill patients, changes in the velocity-time integral (VTI) of the left ventricular outflow tract, measured by transthoracic echocardiography (TTE), are often used to non-invasively assess the response to fluid administration or for performing tests assessing fluid responsiveness. However, the precision of TTE measurements has not yet been investigated in such patients. First, we aimed at assessing how many measurements should be averaged within one TTE examination to reach a sufficient precision for various variables. Second, we aimed at identifying the least significant change (LSC) of these variables between successive TTE examinations. We prospectively included 100 haemodynamically stable patients in whom TTE examination was planned. Three TTE examinations were performed, the first and the third by one operator and the second by another one. We calculated the precision and LSC (1) within one examination depending on the number of averaged measurements and (2) between measurements performed in two successive examinations. In patients in sinus rhythm, averaging three measurements within an examination was enough for obtaining an acceptable precision (interquartile range highest value < 10%) for VTI. In patients with atrial fibrillation, averaging five measurements was necessary. The precision of some other common TTE variables depending on the number of measurements is provided. Between two successive examinations performed by the same operator, the LSC was 11 [5–18]% for VTI. If two operators performed the examinations, the LSC for VTI significantly increased to 14 [8–26]%. The LSC between two examinations for other TTE variables is also provided. Averaging three measurements within one TTE examination is enough for obtaining precise measurements for VTI in patients in sinus rhythm but not in patients with atrial fibrillation. Between two TTE examinations performed by the same operator, the LSC of VTI is compatible with the assessment of the effects of a 500-mL fluid infusion but is not precise enough for assessing the effects of some tests predicting preload responsiveness.

Acute hypoxemic respiratory failure (AHRF), particularly acute respiratory distress syndrome (ARDS), is characterized by marked heterogeneity in lung morphology and mechanics, requiring individualized mechanical ventilation strategies that balance adequate gas exchange with the prevention of ventilator-induced lung injury (VILI). Lung ultrasound (LUS) has become a cornerstone of critical care imaging, allowing differential diagnosis, quantitative assessment of lung aeration, phenotyping of ARDS morphology, and monitoring of disease evolution and complications. However, imaging alone does not provide direct guidance for optimizing ventilator settings. Some modern ventilators enable the rapid bedside acquisition of tidal pressure–volume (PV) loops, allowing tidal hysteresis to be measured and thereby providing complementary physiological information by identifying cyclic opening and closing of lung units and signs of overdistension. Emerging evidence supports the use of tidal hysteresis thresholds to identify insufficient positive end-expiratory pressure (PEEP) associated with tidal recruitment/derecruitment and to guide individualized PEEP titration during decremental PEEP trials. This review discusses the rationale and practical implementation of an integrated approach combining critical care ultrasound and PV loops throughout the management of mechanically ventilated patients with AHRF. We describe how ultrasound can support diagnosis, phenotyping, monitoring of lung aeration, and detection of ventilation-related complications, while PV loops provide a practical physiological framework for optimizing ventilator settings. This approach may provide a comprehensive, non-invasive, and repeatable bedside assessment of lung morphology, aeration, and respiratory mechanics, potentially facilitating personalized mechanical ventilation strategies aimed at reducing the risk of VILI and optimizing patient management.