9: ECHOCARDIOGRAPHIC ASSESSMENT OF LEFT VENTRICULAR SYSTOLIC AND DIASTOLIC FUNCTION

Introduction

Left ventricular (LV) dysfunctions (systolic and diastolic) are common in the critically ill patient. They may be due to preexistent disease (e.g., coronary artery disease [CAD]) or acquired as a part of a clinical syndrome responsible for the intensive care unit (ICU) admission (e.g., septic cardiomyopathy). Clinical examination alone or in combination with chest radiography may be insufficient for assessing LV function in the ICU. Echocardiography will provide crucial information; thus, echocardiographic assessment of LV function is necessary in nearly all ICU patients. Other technologies, such as bioreatance (NICOM) and thermo or marker dilution (LiCO, PICO), may provide additional information that can also be useful. Indwelling Doppler devices assessing aortic blood flow have been utilized with variable degree of success. Finally, carotid artery blood flow measured ultrasonographically has been recently suggested as an alternative to more technically challenging analysis of the transaortic stroke volume (SV) (cardiac output [CO]). All of these methods assist in assessing the LV.

Transthoracic Echocardiography Versus Transesophageal Echocardiography—Hand-Held Devices

Transthoracic echocardiography (TTE) is the modality most frequently utilized in the ICU. In spite of being operator dependent TTE will usually provide clinically useful information that alters the plan of care in nearly 50% of critically ill patients. It is noninvasive, has virtually no contraindications, can be repeated as often as necessary to reevaluate cardiac function after therapeutic interventions (volume resuscitation, inotropic support, vasoconstrictors), and usually requires no more then 5 min to acquire clinically relevant information about cardiac function by the experienced operator.¹ Moreover, it is easy to train intensivists in TTE. Newer generations of the handheld, pocket sized, battery-powered devices are now available and are simple and convenient to operate. They can provide a focused qualitative assessment of the LV systolic function. Handheld devices can be also valuable in ultrasound-guided thoracentesis, paracentesis, and abdominal examination. The role and utility of these devices in the assessment of the hemodynamically unstable ICU patient is still evolving.

Transesophageal echocardiography (TEE) is often considered superior to TTE in the ICU. TTE frequently provides poorer image quality in postoperative patients due to mechanical ventilation (positive end-expiratory pressure [PEEP] >15 cm of H₂O), inability to position the patient, lack of patient cooperation, chest wall edema and obstructed views due to wound dressings, chest tubes, drains, and an open chest or abdomen. In the critical care setting, TTE leads to a successful examination in 50% of attempts,^2,3 in contrast to 90% with TEE.^4,5 There are, however, challenges to the routine performance of TEE in the ICU. The TEE examination requires additional time and expertise when compared with the TTE examination. There is a small, but definite list of absolute and relative contraindications (Chapter 8). Insertion of the probe into the esophagus carries with it a risk of loss of the airway. Additionally, TTE carries with it a small but real risk, ...