Abstract
Heart and lung sharing the same anatomical space are influenced by each other. Spontaneous breathing induces dynamic changes in intrathoracic pressure, impacting cardiac function, particularly the right ventricle. In intensive care units (ICU), mechanical ventilation (MV) and therefore positive end-expiratory pressure (PEEP) are often applied, and this inevitably influences cardiac function. In ventilated patients, the use of positive pressures leads to an increase in intrathoracic pressure and, consequently, to a reduction in the right ventricular preload and thus cardiac output. The clinician working in the intensive care unit must be able to assess the effects MV has on the heart in order to set it up appropriately and to manage any complications. The echocardiographic evaluation of the ventilated patient has the main purpose of studying the right ventricle; in fact, they are the ones most affected by PEEP. It is therefore necessary to assess the size, thickness, and systolic function of the right ventricle. In the mechanically ventilated patient, it may be difficult to assess the volemic status and fluid responsiveness, in fact, the study of the inferior vena cava (IVC) is not always reliable in these patients. In patients with MV, it is preferable to assess fluid responsiveness with dynamic methods such as the end-expiration occlusion (EEO) test, passive leg raise (PLR), and fluid challenge (FC). The study of the diaphragm is also essential to identify possible complications, manage weaning, and provide important prognostic information. This review describes the basis for echocardiographic evaluation of the mechanically ventilated patient with the aim of supporting the clinician in managing the consequences of MV for heart–lung interaction.
Key Points
- Heart-Lung Interactions: Mechanical ventilation affects cardiac output by altering intrathoracic pressure, reducing venous return, and impacting RV preload and afterload.
- Right Ventricular Dynamics: The RV is particularly affected by MV, with assessments focusing on size, wall thickness, and functional parameters like tricuspid annular plane systolic excursion (TAPSE) and fractional area change (FAC).
- Role of PEEP: Positive end-expiratory pressure (PEEP) has contrasting effects, reducing hypoxic vasoconstriction but increasing RV afterload at high lung volumes.
- Echocardiographic Techniques: Includes assessment of inferior vena cava (IVC) dynamics, RV strain, and systolic pulmonary arterial pressure (sPAP) to evaluate hemodynamic status.
- Diaphragm Evaluation: Ultrasound can detect diaphragmatic dysfunction caused by prolonged MV, aiding in the management of weaning challenges.
- Fluid Responsiveness: Dynamic tests like the passive leg raise (PLR) and end-expiration occlusion (EEO) test help predict fluid responsiveness in ventilated patients.
- Hemodynamic Monitoring: Echocardiography is crucial for non-invasive monitoring, enabling real-time adjustments to MV settings and fluid therapy.
- Challenges in ICU: Factors like poor acoustic windows and patient conditions limit echocardiographic accuracy, necessitating skilled operators.
- Prognostic Implications: Echocardiographic findings, such as RV strain and atrial volume changes, correlate with ICU outcomes, including mortality rates.
- Future Directions: Emphasizes research on advanced echocardiographic techniques and integration of findings into personalized ventilation strategies.
