Today, I review, link to, and excerpt from A practical approach to goal-directed echocardiography in the critical care setting. [PubMed Abstract] [Full-Text HTML] [Download Full-Text PDF]. Crit Care. 2014 Dec 1;18(6):681. doi: 10.1186/s13054-014-0681-z.
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Abstract
Urgent cardiac ultrasound examination in the critical care setting is clinically useful. Application of goal-directed echocardiography in this setting is quite distinct from typical exploratory diagnostic comprehensive echocardiography, because the urgent critical care setting mandates a goal-directed approach. Goal-directed echocardiography most frequently aims to rapidly identify and differentiate the cause(s) of hemodynamic instability and/or the cause(s) of acute respiratory failure. Accordingly, this paper highlights 1) indications, 2) an easily memorized differential diagnostic framework for goal-directed echocardiography, 3) clinical questions that must be asked and answered, 4) practical issues to allow optimal image capture, 5) primary echocardiographic views, 6) key issues addressed in each view, and 7) interpretation of findings within the differential diagnostic framework. The most frequent indications for goal-directed echocardiography include 1) the spectrum of hemodynamic instability, shock, and pulseless electrical activity arrest and 2) acute respiratory failure. The differential diagnostic categories for hemodynamic instability can be remembered using the mnemonic ‘SHOCK’ (for Septic, Hypovolemic, Obstructive, Cardiogenic, and (K) combinations/other kinds of shock). RESP-F (for exacerbation of chronic Respiratory disease, pulmonary Embolism, ST changes associated with cardiac or pericardial disease, Pneumonia, and heart Failure) can be used for acute respiratory failure. The goals of goal-directed echocardiography in the unstable patient are: assessing global ventricular systolic function, identifying marked right ventricular and left ventricular enlargement, assessing intravascular volume, and the presence of a pericardial effusion. In an urgent or emergent setting, it is recommended to go directly to the best view, which is frequently the subcostal or apical view. The five views are the subcostal four-chamber view, subcostal inferior vena cava view, parasternal long axis view, parasternal short axis view, and the apical four chamber view. Always interpret goal-directed echocardiographic findings in the context of clinically available hemodynamic information. When goal-directed echocardiography is insufficient or when additional abnormalities are appreciated, order a comprehensive echocardiogram. Goal-directed echocardiography and comprehensive echocardiography are not to be used in conflict with each other.
Indications
Goal-directed echocardiography has now become a reliable tool and can be performed within minutes [17] and is useful for assessing the spectrum of hemodynamic instability, shock, and PEA arrest [2],[32]–[34].
The differential diagnostic categories for hemodynamic instability can be remembered using the mnemonic ‘SHOCK’ (for Septic, Hypovolemic, Obstructive, Cardiogenic, and (‘K’) combinations or other kinds of shock) . ‘S’ stands for the broad category of septic shock due to infection or similar distributive shock from non-infectious causes. Hypovolemia (H) is identified by changes in inferior vena cava (IVC) diameter and by small, underfilled ventricles. Obstructive shock (O) is most frequently due to pericardial tamponade or pulmonary embolism, which manifest differently (see below). Cardiogenic shock (C) is usually characterized by dilated and/or poorly contractile ventricles or marked valvular dysfunction recognized by using color Doppler imaging [5]. When the clinical picture and goal-directed echocardiography do not fit clearly into one of these major categories, other possibilities must be considered – ‘K’, remembered phonetically, for ‘combinations’ and other ‘kinds’. That is, shock may be due to combinations of the above etiologies and rarely due to other disease processes such as adrenal insufficiency, neurogenic shock, and so on.
Goal-directed echocardiography can be combined with thoracic ultrasound imaging [35] and improves diagnostic accuracy over conventional imaging for patients presenting with acute respiratory failure [36]. The most common causes are captured by the mnemonic RESP-F – exacerbation of chronic Respiratory disease, pulmonary Embolism, ST changes associated with acute cardiac or pericardial disease, Pneumonia, and heart Failure. Lung and thoracic imaging (beyond the scope of this review) are an essential component of this examination to additionally identify pleural effusion, pneumothorax, and consolidated or edematous lung [35],[36].
Specific goals
The goal of goal-directed echocardiography is to identify the cause (mnemonic SHOCK) of hemodynamic instability, shock, or PEA arrest and to expedite directed therapies [1],[32]–[34]. To accomplish this, the specific goals are the systematic assessment of 1) left ventricule (LV) systolic function (cardiogenic) [2],[17],[37], 2) right ventricule (RV) size and function [38] (hypovolemia, obstruction [39],[40], cardiogenic), 3) pericardial effusion, potential signs of hemodynamic compromise (obstruction), and 4) size and distensibilty of the IVC for evaluation of volume status (hypovolemia) [14].
A structured approach to accomplishing the goals of goal-directed echocardiography involves specifically asking and addressing key practical questions, as follows. First, does the LV appear significantly dilated or not? Does the LV function appear ‘significantly’ impaired or not? Second, is the RV dilated or not? Third, is there evidence of hypovolemia (small LV, narrow IVC (<21 mm) and collapsing >50% with spontaneous respiration). In the more severe cases of hypovolemia, and in a non-mechanically ventilated patient, an IVC diameter of ≤1 cm usually indicates preload responsiveness [41]. Fourth, is pericardial effusion present (moderate to large)?
Goal-directed echocardiography should note the presence of additional abnormalities but the diagnostic pursuit of these additional findings is accomplished by a comprehensive echocardiographic examination. Specifically, the presence of significant valvular abnormalities, wall motion abnormalities, LV aneurysm, RV hypertrophy, cardiac masses, thrombus, diastolic dysfunction, or a dilated ascending aorta with potential dissection should be pursued with a comprehensive echocardiographic examination, when recognized [1].
