Echocardiography for intensivists
Overview
Since its early use in intensive care unit (ICU) settings by pioneers,1 echocardiography has been increasingly performed in critically ill patients because it provides unparalleled information on central hemodynamics.2 Initially, real-time morphologic and hemodynamic information, ease of use, portability, and safety constituted definite advantages of echocardiography over more invasive techniques, such as right heart catheterization. Subsequently, ultrasound systems have become smaller, higher quality, and less expensive. This facilitated the diffusion of echocardiography in the ICU environment.3
Rapidly, the use of echocardiography by intensivists appeared to be distinct from that of the cardiology community because of specific indications and requirements. Critical care echocardiography (CCE) refers to an examination performed and interpreted by an intensivist to establish diagnoses and guide therapeutic management of patients with cardiopulmonary compromise.4 The required training of intensivists to reach competence in CCE has been diversely implemented among countries, in Europe and worldwide.5 Scientific societies of critical care medicine have recently published international recommendations on the competence4 and the training6 required to perform CCE (see Chapter 61).
This chapter illustrates the current clinical use of echocardiography in the ICU settings and provides insights into future modalities of ultrasound-based clinical assessment of unstable patients with cardiopulmonary compromise.
Critical care echocardiography
Specific requirements of critical care echocardiography
Hemodynamic assessment of ventilated patients with circulatory or respiratory failure is the main indication for performing CCE.2,7,8 As opposed to conventional, state-of-the-art echocardiography performed in the cardiology laboratory, CCE has distinct requirements (Table 27-1). CCE must be available around-the-clock at the time of the clinical deterioration. Transesophageal echocardiography (TEE) is frequently required when the imaging quality of transthoracic echocardiography (TTE) is inadequate. Heart-lung interactions should be taken into account in the interpretation of CCE studies because critically ill patients are commonly mechanically ventilated. CCE may be focused on the hemodynamic assessment by using a qualitative rather than a quantitative approach.9 CCE may be repeated to assess the efficacy and tolerance of induced therapeutic changes as a monitoring tool, or if the patient’s condition changes over time.10 Additional indications of echocardiography in the ICU settings are closely related to the specific recruitment of institutions (Box 27-1) and require extensive training to reach competence.3
TABLE 27-1
Distinct Requirements of Critical Care and Conventional Echocardiography
| Critical Care Echocardiography | Conventional Echocardiography |
| Main indications: cardiopulmonary compromise | Main indications: cardiopathies |
| Performed at the bedside by the ICU physician | Performed in the cardiology laboratory by the sonographer |
| Online interpretation by the ICU physician | Off-line interpretation by the cardiologist |
| Interpretation in light of the critical care medicine background of the physician | Interpretation in light of the cardiology background of the physician |
| Guides diagnostic workup and invasive procedures | Expertise allows identification and interpretation of complex findings |
| Around-the-clock availability | Daytime schedule |
| Ventilated patients (heart-lung interactions) | Spontaneously breathing (out)patients |
| TEE frequently required and easy to perform | TTE is most commonly performed |
| Frequently goal-oriented examination | State-of-the-art exhaustive examination |
| Qualitative or quantitative evaluation using simple yet robust parameters | Quantitative assessment using all existing imaging tools |
| Immediate diagnostic/therapeutic impact | Delayed diagnostic/therapeutic impact |
| Monitoring tool/short-term follow-up | Diagnostic tool/long-term follow-up |
Transthoracic versus transesophageal echocardiography
TTE is the first-line approach because of its versatility, tolerance, and availability.7,11 It typically allows an optimal Doppler beam alignment with intracardiac flows and a broader field of examination of relatively superficial anatomic structures (Table 27-2).
TABLE 27-2
Respective Advantages of Transthoracic and Transesophageal Echocardiography in the ICU Settings
| Favors Transthoracic Echocardiography | Favors Transesophageal Echocardiography |
| Versatility, strictly noninvasive, availability, no contraindication (even in spontaneously breathing patients) Assessment of superficial anatomic structures (apical thrombus, pericardial space, inferior vena cava) Optimal alignment of Doppler beam with transvalvular blood flows (mitral, aortic, and tricuspid valves), and abnormal jets (valvulopathy, left ventricular outflow tract obstruction) Evaluation of pulmonary artery pressure (tricuspid and pulmonary regurgitant jets) |
Consistent high imaging quality, reproducibility, and stability of imaging planes (especially in ventilated patients) Assessment of deep anatomic structures (great vessels, base of heart, mediastinum, prosthetic valves, atria, and appendages) Precise identification of the mechanism of certain native or prosthetic valve dysfunctions (eccentric mitral regurgitation, prosthetic valve dysfunction) Identification of intracardiac shunts Identification of great vessel diseases (proximal pulmonary embolism, spontaneous or traumatic acute aortic conditions) |
TEE is usually used as an adjunct or subsequent test to TTE when surface examination is nondiagnostic. This may be related to poor imaging quality or to the inaccessibility of deep anatomic structures. Because of reduced interference with image acquisition, TEE has a greater diagnostic capability than TTE in ventilated ICU patients.12 TEE is first performed when examination of deep anatomic structures is required, especially after cardiac surgery.7,11 Finally, TEE provides more reproducible imaging planes than TTE when a hemodynamic monitoring is needed in unstable patients (see Table 27-2). Nevertheless, TEE is cumbersome to perform repeatedly and is contraindicated in the presence of any risk of esophageal injury (see Chapter 30). In ventilated ICU patients, TEE is safe, and unsuccessful probe insertion is rare when using laryngoscopic guidance under adequate sedation.8 In spontaneously breathing patients, the major risk of TEE is related to the development of acute respiratory failure precipitated by the esophageal intubation.13 Accordingly, TEE should be discouraged in unstable patients who are not on ventilatory support, especially when a tamponade or a massive pulmonary embolism is suspected.10
Impact of critical care echocardiography on patient management
CCE has a direct impact on management in a large proportion of ICU patients.8,10 Although TEE has been shown to prompt reoperation without further workup in patients with complicated open-heart surgery and has a greater therapeutic impact than TTE,12 surface echocardiography is also diagnostic in patients with shock.14 CCE frequently corrects initial diagnoses derived from invasive hemodynamic monitoring.10 When performed at the time of the acute insult, CCE best depicts the origin of the cardiopulmonary compromise before the effects of therapy, which may rapidly alter the hemodynamic profile. The anticipated therapeutic impact of CCE is maximal in the most unstable ICU patients at the time of examination.
Clinical use of critical care echocardiography
Circulatory failure
Septic shock
Hemodynamic disturbances associated with septic shock are complex and may variously associate with hypovolemia, vasoplegia, and right ventricular (RV), or left ventricular (LV) dysfunction.15 When performed during the initial phase of septic shock in fluid-resuscitated patients, who are usually under vasopressor support, CCE helps the intensivist in guiding acute therapy.16
CCE provides information on cardiac preload, reflected by end-diastolic ventricular volume or area (see Chapter 39), and allows prediction of fluid responsiveness in both mechanically ventilated and spontaneously breathing septic patients (see Chapter 40). CCE findings consistent with profound hypovolemia typically are associated with small cardiac cavities end-systolic obliteration of LV cavity in the presence of a hyperkinetic ventricle, small inferior vena cava size with full inspiratory collapse in spontaneously breathing patients, and large oscillations of interatrial septum that reflect low pressures of both atria (Figure 27-1). Nevertheless, most of these findings individually have a poor diagnostic capacity17,18 because “static” indices of preload fail to accurately predict the cardiac response to fluid loading.19 Of note, in fluid-resuscitated septic patients, overt hypovolemia is uncommon, and CCE is then useful in predicting fluid-responsiveness. Preload-dependent ventilated patients typically exhibit marked respiratory variations of aortic Doppler velocities and of the size of both the superior and inferior vena cavae.20 In these patients, fluid loading significantly increases the stroke distance of LV outflow (i.e., stroke volume) (Figure 27-2). In patients with spontaneous breathing activity or nonsinus rhythms, the effect of passive leg raising on LV outflow stroke distance helps in predicting responders to a fluid challenge from nonresponders.20
Figure 27-1 Profound hypovolemia detected by transesophageal echocardiography in a hypotensive ventilated patient after cardiac surgery. M-mode tracings obtained from the transgastric short-axis view of the left ventricle depict the presence of a virtual ventricular cavity with end-systolic obliteration (left panel), and the progressive increase of the ventricular size secondary to two consecutive fluid challenges which reflects increased preload (middle and right panels). Please note the improved thickening of left ventricular walls, which reflects the increase of stroke volume secondary to blood volume expansion in this fluid responder. LV, Left ventricle.
Figure 27-2 Assessment of fluid responsiveness by using transesophageal echocardiography in the early course of a ventilated patient with septic shock and sinus rhythm. At baseline, the stroke distance of left ventricular outflow was reduced (14.2 cm), reflecting decreased stroke volume (upper left), and associated with marked respiratory variations of maximal Doppler velocities (middle left) and superior vena cava diameter (lower left), which both suggested preload dependency. After 500-mL fluid loading, left ventricular outflow Doppler disclosed a 39% increase of stroke distance (19.7 cm), which confirmed fluid responsiveness (upper right), and both the respiratory variations of maximal Doppler velocities (middle right) and superior vena cava diameter (lower right) were attenuated. I, Insufflation; E, expiration.
In approximately one third of patients examined at the early phase of septic shock, CCE clearly depicts a LV systolic dysfunction (Video 27-1
). The myocardial depression related to septic shock positively responds to inotropic agents (Video 27-2), and fully recovers in survivors, with the treatment of sepsis, regardless of its severity.16,21,22 In contrast with congestive heart failure, LV filling pressures are typically not elevated.
