Transesophageal Echocardiography for Monitoring Cardiopulmonary Interactions

Cardiopulmonary interactions were initially described in animals and in humans by using the pulmonary artery catheter, but a limitation was the inability to accurately evaluate the distending pressure of the cardiac and vascular cavities, especially in patients submitted to a significant increase in intrathoracic pressure. Echocardiography is a useful device for the assessment of cardiopulmonary interactions by its ability to (i) measure in 2-D mode heart cavity size, which is related to transmural pressures, and (ii) record pulsed wave Doppler flow, which is related to the intravascular pressure difference between two cavities. Moreover, this evaluation is possible on a beat-by-beat basis throughout the respiratory cycle by visualizing the airway pressure tracing on the screen of the echocardiogram monitor. The transesophageal approach is more suitable than the transthoracic approach for critically ill patients because transesophageal echocardiography is less operator-dependent and more reproducible, can visualize structures such as the superior vena cava, and yields better image quality than can be routinely obtained with transthoracic echocardiography. The primary limitation of transesophageal echocardiography is the contraindications for inserting an esophageal probe and that it only can be performed in patients who are sedated under invasive mechanical ventilation. In such conditions, it may help optimize the management of patients with circulatory or respiratory compromise.