Cardiac Tamponade Under Positive-Pressure Ventilation: Pathophysiological Insights and Implications for Diagnosis.

In mechanically ventilated patients, the clinical and echocardiographic presentation of pericardial tamponade differs from the classic spontaneous-breathing paradigm. Positive-pressure ventilation (PPV) increases pleural and pericardial pressures, narrows the transmural filling gradient, augments ventricular interdependence, and can precipitate tamponade physiology at smaller effusion volumes. Consequently, the classic Doppler cues, such as large respiratory variation in mitral/tricuspid inflow, are commonly blunted, reversed, or absent, and right-sided chamber collapse can be intermittent or phase-shifted across the ventilatory cycle. Therefore, diagnosis depends on integrating clinical suspicion, hemodynamics, and multiple echocardiographic features, including effusion morphology (often loculated/posterior in the postoperative setting), right-atrial systolic and right-ventricular diastolic collapse (timed to the cardiac cycle), venous congestion surrogates (inferior vena cava plethora and superior vena cava/hepatic venous Doppler findings), and direct evidence of reduced stroke volume. Transthoracic echocardiography (TTE) is fast and, when the window is good, can provide a safe guide to life-saving pericardiocentesis. Thus, TTE is established as a first-line approach in both intra-hospital emergencies and in prehospital settings. However, in the context of PPV, tamponade may be underrecognized because suboptimal acoustic windows, postoperative dressings, emphysema, thoracic trauma, or prone positioning can limit TTE. Across 40 physiological, diagnostic accuracy, and impact studies, early TTE after cardiac surgery showed only modest performance in surgically confirmed tamponade (area under the curve of approximately 0.64 and a positive predictive value of approximately 58%). Meanwhile, about half of the postoperative effusions were predominantly posterior or loculated. In mechanically ventilated intensive care unit cohorts, transesophageal echocardiography (TEE) resolved almost all prespecified clinical questions and changed therapy more often than TTE (97% vs. 38% and 36% vs. 16%, respectively). These findings support a physiology-anchored approach in which TTE remains first-line; meanwhile, TEE should be considered early when clinical suspicion is moderate-to-high, and TTE is nondiagnostic or when posterior/loculated or regional tamponade is suspected during PPV.