Critical care echocardiography: training, imaging, and indications

Learning objectives.

By reading this article, you should be able to:

• •Explain the competencies of basic critical care echocardiography.
• •Review the approaches to train and maintain competency in critical care echocardiography.
• •Identify cardinal views in transthoracic echocardiography.
• •Evaluate the application of critical care echocardiography to manage shock.

Key points.

• •Basic competence in critical care echocardiography is standard of care for all intensivists.
• •Training competency in critical care echocardiography requires didactic training coupled with completion of a portfolio, assessment of competency, and ongoing quality assurance.
• •Use of echocardiography in the ICU requires technical skills and cognitive experience to integrate findings into clinical management.
• •Transthoracic echocardiography is the default technique in the ICU for goal-directed imaging, but transoesophageal echocardiography can be used when transthoracic imaging yields inadequate images.

The use of critical care ultrasound has evolved over the past two decades accompanied by major developments in ultrasound technology. Although ultrasound was originally used by intensivists for guidance during procedures (e.g. during central venous catheter insertion), modern day use now includes both general ultrasound and critical care echocardiography (CCE).

The term CCE refers to a goal-directed echocardiographic examination performed by the treating clinician with immediate application of the findings to patients' care. Critical care echocardiography may involve transthoracic echocardiography (TTE), transoesophageal echocardiography (TOE), or both. When performed by appropriately trained intensivists, CCE provides time-sensitive information that can be used to optimise the patient's haemodynamic state.¹

Although it is difficult to quantify the benefits of CCE in terms of mortality, there is strong evidence that CCE is safe and can lead to appreciable changes in clinical management.2, 3, 4 However, the efficacy and safety of CCE relies on the competency of the practitioners, and incorrect or missed diagnoses have the potential to cause significant harm.

As CCE continues to proliferate, ongoing education is essential in improving the quality and safety of its use. In this article, we discuss the current definitions of basic CCE competencies, outline a framework for training and provide an overview of clinical applications in the ICU.

Competencies and training framework for critical care echocardiography

In 2009, the American College of Chest Physicians and La Société de Réanimation de Langue Française published a consensus statement that offered the first comprehensive multinational statement of critical care ultrasound competencies that included CCE.⁵ The consensus statement defined a framework consisting of general ultrasound (thoracic, abdominal and vascular) and CCE. Critical care echocardiography was separated into basic and advanced competencies, based on the cognitive skills required for image interpretation and recognition of clinical syndromes (Table 1). The authors did not separate TTE and TOE into basic or advanced competencies, as the framework regarded TOE as useful in both basic and advanced imaging, particularly when TTE was limited by poor acoustic windows.

Table 1.

Summary of guidelines on basic competencies in critical care echocardiography (CCE). CCE, critical care echocardiography; IVC, inferior vena cava; LV, left ventricular; RV, right ventricular; TAPSE, tricuspid annular plane systolic excursion; TOE, transoesophageal echocardiography.

American College of Chest Physicians and La Société de Réanimation de Langue Française (SRLF) (2009)5
Required cognitive skills in image interpretation	Required cognitive skills in recognition of clinical syndromes
Global LV size and systolic function	Severe hypovolaemia
Homogeneous/heterogeneous LV contraction pattern	LV failure
Global RV size and systolic function	RV failure
Assessment for pericardial collection/tamponade	Tamponade
IVC size and respiratory variation	Acute massive left-sided valvular regurgitation
Basic colour Doppler assessment for severe valvular regurgitation	Circulatory arrest during resuscitation
Society of Critical Care Medicine: Guidelines for Appropriate use of Cardiac Ultrasonography (2016)6
Summary of strong recommendations for basic CCE (Grade 1)	Summary of conditional recommendations for basic CCE (Grade 2)
Preload responsiveness, ventilated	LV dysfunction, sepsis
LV systolic function	RV infarction
Acute cor pulmonale or RV infarction	Asystole
Symptomatic pulmonary embolism	Pulseless electrical activity
Resuscitation in sepsis	TOE in cardiac arrest
Ventricular tachycardia/fibrillation
Pericardial effusion
Native valvular dysfunction, mechanical valvular dysfunction
Prosthetic valve endocarditis
Blunt chest trauma for pericardium, penetrating chest trauma
ESICM recommendations for core critical care ultrasound competencies (2020)7
Competencies in basic CCE	Clinical syndromes in basic CCE
a. LV: size (qualitative), Function (qualitative)	Severe hypovolaemia
b. Contraction pattern (qualitative), valve disease (qualitative, colour)	LV failure, RV failure
RV size (qualitative), systolic function (quantitative)	Tamponade
c. TAPSE, RV/LV area ratio, valve disease (qualitative, colour)	Acute cor pulmonale

Updates on basic competencies in critical care echocardiography

Since 2009, there have been further efforts to refine the definition of core CCE competencies (Table 1). In an effort to develop evidence-based consensus, in 2016 Levitov and colleagues published guidelines for the appropriate use of cardiac ultrasonography in critically ill patients.⁶ Forty-five statements were considered by a group of international experts using a modified Delphi technique to formulate recommendations.

More recently, Wong and colleagues published updated recommendations for critical care ultrasound competencies based on a three-round Delphi process amongst 32 ultrasound experts nominated by the European Society of Intensive Care Medicine.⁷ These recommendations were designed to create a clear standard for training and competency in ultrasound and included technical aspects such as qualitative and quantitative assessments.

Framework of training

Critical care echocardiography competency requires training to both perform and interpret images, while integrating findings to the clinical context and the patient's haemodynamic state. As evident by the variability in definitions of CCE competency, there is a lack of universal consistency on what constitutes a CCE competent intensivist. The common framework adopted by most national working groups and intensive care societies include four key stages: (i) introductory didactic training, (ii) portfolio completion, (iii) competency assessment and (iv) ongoing maintenance of competence.⁸ The modality of training and methods of evaluation vary across regions.

Didactic training

Didactic training involves introductory training in the form of face-to-face teaching or online courses. Courses should provide a foundation in the principles of ultrasound, image acquisition, probe manipulation, and include the cognitive skills required for interpreting images.

Portfolio completion

All programmes for critical care ultrasound require trainees to keep a portfolio or logbook, supervised by an appropriate expert who can provide feedback on image quality and correct interpretation of pathology.

Competency assessment

Assessment of CCE skills is not well defined with little high-quality evidence on the best methods of competency assessment.⁹ Competency is typically assessed through formal examinations administered by regulatory bodies.

Quality assurance and maintenance of competence

All intensivists are expected to engage in continual maintenance of competence and consider a period of retraining after absence from routine use.

Accreditation in critical care echocardiography

To help provide consistent standards, several regulatory bodies have established accreditation programmes for CCE. Popular pathways for general CCE accreditation include the European Diploma in Advanced Critical Care Echocardiography, Focused Intensive Care Echocardiography, National Board of Echocardiography Special Competency in Critical Care Echocardiography and the Diploma of Diagnostic Ultrasound Critical Care (Table 2).

Table 2.

Summary of popular critical care echocardiography accreditation pathways and requirements.¹⁰ CCE, critical care echocardiography; DDUS, diploma of diagnostic ultrasound; EDEC, European diploma in advanced critical care echocardiography; FICE, focused intensive care echocardiography; NBE, National Board of Echocardiography; OSCE, observed standardised clinical examination; TOE, transoesophageal echocardiography; TTE, transthoracic echocardiography.

Accreditation	Country	Duration (yrs)	Modality	Assessment	Logbook
EDEC	Europe	1–2	TTE and TOE	•Formal examination •OSCE	•100 TTE •30 TOE
FICE	UK	1	TTE	•E-learning •Supervisor	•50 TTE
NBE CCE	USA	2	TTE and TOE (optional)	•Formal examination	•150 TTE for TTE certification; optional 50 TOE can be completed for additional TOE certification
DDUS	Australasia	2 years	TTE and TOE	•Formal examination •Case studies	•300 TTE •50 TOE •50 Lung •50 Vascular

Essentials of critical care echocardiography

Equipment and minimum requirements

Minimum standards for ultrasound equipment in ICUs should cater to both basic and advanced competencies and support the progression of CCE by practitioners (Table 3).¹² These goals can be achieved with dedicated ultrasound platforms that are suitable for both general ultrasound and CCE. The platform should support TOE imaging and come with cardiac quantification packages (Fig. 1).

Table 3.

Minimum standards for ultrasound equipment used in critical care echocardiography.¹¹ 2D, two dimensional; M-mode, motion mode.

1. Dedicated phased array cardiac probe with harmonic capabilities. 2. Multiplane transoesophageal probe 3. 2D and M-Mode capabilities with cardiac software package 4. Spectral Doppler (pulse wave and continuous wave) 5. Colour Doppler 6. Tissue velocity imaging and quantification 7. Cardiac quantification package (basic and advanced with automation)

Fig 1.

Examples of currently available multipurpose ultrasound machines available with quantitative cardiac software, multi-purpose probe support and capabilities for transoesophageal echocardiography. (A) Fujifilm Sonosite LX, (B) Mindray M9 Premium and (C) Philips 5500 Series.

Transthoracic echocardiography

Transthoracic echocardiography is the most readily available imaging modality for CCE and has several distinct advantages over TOE. Transthoracic echocardiography can be readily used in awake patients, is non-invasive, and has no significant contraindications. However, TTE examination in the ICU can be challenging in the presence of dressings and chest drains. Image quality may be reduced by factors such as obesity, positive pressure ventilation, the presence of subcutaneous emphysema, or an inability to position the patient optimally.

The number of cardiac imaging views required during a CCE study depends on the indication and user's experience. The basic CCE user should be able to address the majority of clinical questions using five imaging windows (Fig. 2)¹¹:

• (i)
  Parasternal long axis view

  • a.
    Probe position: the probe should be placed with the transducer orientation marker pointing to the patient's right shoulder, usually along the 3rd or 4th left intercostal space just to the left of the sternum. The tail of the probe should be tilted towards the patient's left hip.
  • b.
    Key structures and use: the following structures can be visualised: right ventricular outflow tract (RVOT), aortic valve (AV), left ventricular outflow tract (LVOT), mitral valve (MV), left atrium (LA), pericardium, left ventricle (LV, anteroseptal and inferolateral walls), and the descending thoracic aorta. The parasternal long axis view allows for evaluation of left ventricular size and function, LVOT diameter, aortic (AV) and mitral (MV) morphology, and LA size. Although the AV and MV are not parallel to the ultrasound beam in this view, colour Doppler imaging can still be used to assess for flow proximal and distal to the valves, which might suggest valvular stenosis or insufficiency. Pericardial fluid collections can also be evaluated in a limited fashion from this view.
• (ii)
  Parasternal short axis view

  • a.
    Probe position: the probe should be placed with the transducer orientation marker pointing to the patient's left shoulder, usually along the 3rd or 4th left intercostal space just to the left of the sternum. This view can be obtained by rotating the probe 90° clockwise from the parasternal long axis view. Although different imaging planes can be assessed from this view, the short axis view or the LV at the level of the papillary muscles is most often used in basic CCE.
  • b.
    Key structures and use: the following structures can be seen: both papillary muscles (which should appear symmetric when the image is correctly obtained), right ventricle (RV), LV, pericardium and ventricular septum. The parasternal short axis view allows for evaluation of left ventricular systolic function, left ventricular wall motion, the shape and motion of the ventricular septum (for assessment of RV pressure or volume overload) and evaluation of pericardial fluid collections. Users should ensure that the left ventricular cavity appears circular, as an oval-shape indicates off-axis imaging, which may lead to errors when assessing left ventricular function.
• (iii)
  Apical four-chamber view

  • a.
    Probe position: the probe should be placed with the transducer orientation marker pointing to the patient's left shoulder at the 4th or 5th left intercostal space along the midaxillary line. The tail of the probe should be tilted towards the patient's head. The ventricular septum should be aligned in a vertical position in the middle of the screen with both tricuspid valve (TV) and MV visible. A non-standard apical five-chamber view can be obtained by tilting the tail of your probe towards the patient's feet.
  • b.
    Key structures and use: the following structures can be visualised: right atrium (RA), RV, MV, TV, LA, LV (anteroseptal and inferoseptal walls), and the pericardium. The apical four-chamber view allows for evaluation of left and right ventricular size and function and, importantly, a comparison of the relative sizes of the left and right ventricles. The mitral and tricuspid valves can also be assessed, and colour Doppler used for qualitative assessment of regurgitant lesions. A modified five-chamber view allows users to visualise the LVOT and AV and assess for high pressure gradients (LVOT obstruction, AV stenosis) and measurement of stroke volume using spectral Doppler.
• (iv)
  Subcostal four-chamber view

  • a.
    Probe position: the probe should be placed on the upper abdomen, inferior to the xiphoid process in the midline with the transducer orientation marker pointing to the left shoulder of the patient. The tail of the probe should be tilted towards the patient's feet.
  • b.
    Key structures and use: the following structures can be visualised: RV, LV, RA, LA and pericardium. The subcostal four-chamber view allows for rapid qualitative assessment of left and right ventricular systolic function and size and for the assessment for pericardial fluid collections and cardiac tamponade.
• (v)
  Subcostal inferior vena cava view

  • a.
    Probe position: the probe should be placed inferior to the xiphoid process in the midline with the transducer orientation marker pointing cephalad. Alternatively, rotate the probe 90° degrees anticlockwise from the subcostal four-chamber view.
  • b.
    Key structures and use: the following structures can be visualised: inferior vena cava (IVC), RA-IVC junction and hepatic veins. The subcostal IVC view allows for evaluation of IVC diameter, respiratory variation, and hepatic vein Doppler (advanced users).

Fig 2.

Minimum transthoracic echocardiography views for critical care echocardiography (CCE) to facilitate basic assessment and example of phased-array probe suitable for transthoracic echocardiography. A4C, apical-four chamber; AV, aortic valve; DTA, descending thoracic aneurysm; HPV, hepatic vein; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; MV, mitral valve; PLAX, parasternal long axis; PSAX, parasternal short axis; RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract; S4C, subcostal four chamber, ; SLAX, subcostal long axis.

Transoesophageal echocardiography

If TTE is not feasible or associated with poor image quality, TOE is a safe and useful alternative.¹³ When incorporated into core speciality training, TOE performed by intensivists or emergency physicians is accurate and has a high diagnostic yield.^3,14 Observational data indicate that TOE performed by intensivists has comparable diagnostic accuracy to TOE performed by cardiologists.¹⁵ Perhaps the biggest obstacle to intensivists becoming proficient in TOE is the limited availability of appropriate supervision in image acquisition and evaluation of competency.

Common indications for TOE in the ICU include assessment of shock when TTE views are not possible, assessment of valvular abnormalities, management of cardiac arrest and assessment of great vessels for pathologies such as aortic dissection.

A comprehensive TOE examination, as performed by cardiac anaesthetists and cardiologists, includes 28 standard views supplemented with Doppler and three-dimensional imaging. By contrast, intensivists who have basic CCE competency can perform a goal-directed TOE examination for evaluation of haemodynamic instability using just four views (Fig. 3).¹⁶ Studies have shown that competency in performing a goal-directed TOE examination can be achieved after 10–30 supervised studies.¹⁷ Detailed review of TOE views and clinical applications is beyond the scope of this article.

Fig 3.

Resuscitative transoesophageal views with multiplane degrees for reference and structures that can be visualised in each view. (A) (mid-oesophageal four-chamber view) is ideal for global assessment of left and right ventricular function and for assessment of mitral and tricuspid valve disease. Pericardial fluid collections can also be visualised. (B) (mid-oesophageal long axis view) can be used during cardiac arrest to assess chest compression position and for assessment of dynamic left ventricular outflow tract obstruction, aortic and mitral valve disease, and global left ventricular function. (C) (mid-oesophageal bicaval view) is useful for assessing the superior vena cava for fluid responsiveness but also for use during cannulation for extracorporeal membrane oxygenation. (D) (transgastric mid-papillary short axis view) can be used for global left ventricular function and identification of segmental wall motion abnormalities. AV, aortic valve; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; LVOT, left ventricular outflow tract; MV, mitral valve; RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract; SVC, superior vena cava; TV, tricuspid valve.

Contraindications to TOE

Transoesophageal echocardiography is a semi-invasive procedure with a low risk of complications. In an observational dataset of >10,000 TOE examinations, the rate of major complications ranged from 0.2% to 0.5%, and the mortality risk was <0.01%.¹⁸ Major complications included oropharyngeal injuries, gastrointestinal (GI) perforation and bleeding.

Absolute contraindications to TOE include perforation of the upper GI tract, structural oesophageal pathology (stricture, tumour, diverticulum), recent upper GI surgery and active upper GI bleeding. In the absence of contraindications, TOE can be used safely by intensivists using goal-directed protocols.¹⁹

Clinical applications of critical care echocardiography

In patients with critical illness, CCE can be used to rapidly evaluate the aetiology of shock, respiratory failure, or cardiac arrest, expediating diagnosis and guiding treatment.

Assessment of shock and hypotension

Focussed CCE allows shock to be rapidly evaluated at the bedside. Identifying the mechanism(s) of shock allows clinicians to initiate further investigations where appropriate (e.g. CT aortogram, coronary angiogram), while simultaneously escalating care to address specific haemodynamic states (e.g. cardiac tamponade, hypovolaemia, pulmonary embolism). Findings on CCE can lead to interventions, such as the infusion of i.v. fluids, commencing inotropes and vasopressors and even initiating extracorporeal life support.

The mechanisms, causes and typical echocardiographic findings in patients with hypotension and shock are summarised in Table 4.

Table 4.

Echocardiographic assessment of hypotension and shock. AMI, acute myocardial ischaemia; HOCM, hypertrophic obstructive cardiomyopathy; IVC, inferior vena cava; LV, left ventricular; LVEDA, left ventricular end diastolic area; LVESA, left ventricular end systolic area; LVH, left ventricular hypertrophy; LVOT, left ventricular outflow tract; MR, mitral regurgitation; PAH, pulmonary arterial hypertension; RA, right atrium; RV, right ventricular; SWMA, segmental wall motion abnormalities; TAPSE, tricuspid annular plane excursion; TV, tricuspid valve.

Mechanism	Cause	Typical echocardiographic findings
Hypovolaemia	Bleeding, inadequate fluid resuscitation, extrarenal fluid losses, dehydration, etc.	•Left ventricle hyperdynamic with end-systolic effacement •Small left ventricle with reduced LV end-diastolic area and end-systolic area •Right ventricle normal or small size •IVC collapsed
Low LV afterload (distributive shock)	Vasoplegia, septic shock, toxidromes (e.g. antihypertensives), spinal shock, post-cardiopulmonary bypass, anaphylaxis	•Left ventricle hyperdynamic or normal function •Normal LVEDA reduced LVESA •Right ventricle normal size or small size with normal wall thickness •IVC collapsed
RV failure	Massive pulmonary embolism	•Right ventricle severely dilated with normal wall thickness •Severe RV systolic dysfunction (TAPSE/qualitative) •Small underfilled LV cavity •Displacement of interventricular septum •Plethoric IVC
	Decompensated chronic RV failure (e.g. PAH)	•Right ventricle severely dilated with increased wall thickness •Severe RV systolic dysfunction •Small underfilled LV cavity •Plethoric IVC •Displacement of interventricular septum
Acute myocardial depression	Stress-induced cardiomyopathy	•Severely impaired LV function •SWMAs beyond distribution of coronary artery with akinesia of the apical and mid-ventricular segments; preserved basal segments •Dilated left ventricle—classically with apical ballooning •Normal RV size and function
	Septic cardiomyopathy—particularly bacterial septic shock such as acquired gram-positive infections (e.g. pneumococcus, meningococcal, Staphylococcus aureus)	•Severely impaired LV dysfunction, RV dysfunction, or both •Normal LV and RV size and wall thickness •Global LV and RV dysfunction •Minimal SWMAs •Normal valvular function
	Fulminant myocarditis	•Normal LV and RV size and wall thickness •Global LV and RV dysfunction •Extensive SWMAs (multiple territories) •Normal valvular function
Acute myocardial ischaemia	Type 1 myocardial infarction or Type 2 myocardial infarction	•Impaired LV function, RV function, or both with SWMAs associated with coronary artery distribution. •Normal LV/RV size and wall thickness •Plethoric IVC if in cardiogenic shock •AMI complications: acute MR from papillary muscle rupture
Decompensated chronic left ventricular failure	Chronic heart failure with decompensation either as a result of acute myocardial infarction as per row above, progression of underlying cause, or inadequate medical management	•Severely impaired LV function with dilated LV size •Globally depressed LV function without SWMA •RV may be normal or depressed secondary to LV failure •Plethoric IVC
Cardiac tamponade	Trauma, neoplasm, bleeding, post-cardiac surgery, inflammatory or infectious	•Significant pericardial effusion •Diastolic collapse of RA and RV •Plethoric IVC with loss of respiratory variation •Normal LV size and function •Doppler pulsus paradoxus of MV or TV inflow velocities
Dynamic LVOT obstruction	Sepsis, vasoplegia, post-cardiac surgery, LV hypertrophy, dehydration, post-myocardial infarction, HOCM, stress-induced cardiomyopathy	•Hyperdynamic LV •Mitral regurgitation, systolic anterior motion of the MV •Aliasing of colour doppler at the LVOT •High-velocity late peaking continuous wave Doppler signal •Additional findings: thickened LV wall in HOCM or LVH
Type A aortic dissection	Connective tissue disease, trauma, hypertension, inflammatory aortopathy, cocaine intoxication, other	•Normal LV and RV size and function •SWMAs if coronary ostia involved. •Intimal flap present at aortic root with or without haematoma •Dilated aortic root with aortic regurgitation •Pericardial effusion

Acute left ventricular failure

Left ventricular function can be rapidly assessed in multiple views using both TTE and TOE. While the gold standard for quantifying left ventricular ejection fraction requires techniques such as Simpson's biplane method of disks, quantitative assessment is unnecessary during resuscitation. Instead, visual estimation of ejection fraction as normal (Fig. 1 online video), moderately depressed, or severely depressed (Fig. 2 online video) using standard resuscitative views, has been shown to closely correlate with calculated ejection fraction by both expert and non-expert readers.^20,21

Assessment for the presence or absence of segmental regional wall motion abnormalities in the parasternal short axis view can be done by practitioners with basic CCE competency. When combined with qualitative assessment of left ventricular size and global function, the presence of segmental wall motion abnormalities may indicate the need for supportive therapies (e.g. inotropic drugs, extracorporeal life support), further investigation (coronary angiography), or definitive treatment (e.g. percutaneous coronary revascularisation).

Acute right ventricular failure

Assessment for haemodynamically significant right ventricular failure involves evaluating RV size, right ventricular function and the motion of the ventricular septum. While a dilated RV does not always indicate acute right ventricular failure, the absence of right ventricular dilation is helpful in excluding the RV as a source of shock.

Right ventricle size should be evaluated in the apical four-chamber view (Fig. 3 online video), with both the mitral and tricuspid valves visualised in the same plane. Right ventricular dilation is present when the RV is greater than two-thirds the size of the LV. Severe right ventricular dilation is present when the RV is equal or larger in size than the LV.

Right ventricular function is best assessed in an apical or subcostal four-chamber view by evaluating the motion of the tricuspid annulus during systole (Fig. 4). A tricuspid annular plane systolic excursion (TAPSE) <16 mm indicates impaired right ventricular systolic function.

Fig 4.

Example of severe right ventricular dysfunction on transthoracic echocardiography. (A) Parasternal short axis demonstrating large right ventricle with flattening of the interventricular septum in systole and diastole (see accompanying Fig. 4 online video). (B) apical four-chamber demonstrating an enlarged right ventricle (greater in size than left ventricle) with impaired longitudinal motion of the tricuspid valve annulus. (C) M-mode imaging across the tricuspid valve showing reduced tricuspid annular plane systolic excursion <16 mm.

Motion of the ventricular septum is best assessed in the parasternal short axis view (Fig. 4 online video). Flattening of the ventricular septum in systole suggests RV pressure overload (e.g. caused by pulmonary embolism) and flattening in diastole suggests volume overload (e.g. from excessive volumes of i.v. fluids).

The finding of acute right ventricular dysfunction during CCE can suggest a specific diagnosis and indicate the need for further interventions. For example, right ventricular dilation in association with impaired systolic function raises the possibility of pulmonary embolism, indicating the need for a CT pulmonary angiogram and—if the diagnosis is confirmed—interventions, such as anticoagulation and thrombolysis. Several common ICU interventions risk worsening right ventricular function, such as aggressive resuscitation with i.v. fluids or positive pressure ventilation with high PEEP. Thus, a finding of acute right ventricular dysfunction may lead clinicians to avoid interventions that worsen right ventricular function.

Cardiac tamponade

Cardiac tamponade is an important cause of shock that is essential to exclude. In general, cardiac tamponade is easily diagnosed with TTE, with the subcostal four-chamber view being particularly helpful. However, in some situations—notably cardiac surgery—TOE may be required to fully delineate the problem. After cardiac surgery, localised collections of clotted blood overlying the LA or RA can easily be missed with TTE.

Although there is no size cut-off for diagnosing clinically significant pericardial collections, in general a maximum diameter <1 cm may be categorised as small and unlikely to cause severe haemodynamic instability.²² Care must be taken when excluding pericardial tamponade after cardiac surgery, as small collections that have formed rapidly can cause marked haemodynamic instability—especially in the presence of impaired ventricular function.

Additional findings on CCE examination in patients with pericardial tamponade include the presence of a distended IVC, collapse or invagination of the RV during diastole and collapse of the RA during systole. Advanced CCE competency includes assessing for evidence of respiratory variability in the inflow velocity to the TV. In spontaneously breathing patients, >60% decrease in the TV peak E-wave velocity during inspiration (or >30% decrease in mitral peak E-wave velocity) is consistent with pericardial tamponade.

The presence of a pericardial collection coupled with clinical features of shock should prompt consideration of drainage.

Hypovolaemia

Intravenous fluids are is the mainstay of initial resuscitation for shock. Although inadequate volumes of i.v. fluid can be harmful, giving excessive volumes is associated with increased mortality.²³

In the absence of clear clinical markers of hypovolaemia (e.g. documented blood loss), clinicians can use echocardiographic measurements of ‘fluid responsiveness’ to predict benefit and ‘congestion’ for indication of harm from further i.v. fluids. The techniques associated with these assessments require competency in advanced CCE imaging modalities, such as spectral Doppler, and require a high level of skill and experience to interpret correctly.²⁴ Echocardiographic indices of fluid responsiveness are summarised in Table 5.

Table 5.

Echocardiographic assessment of fluid responsiveness and venous congestion. A5C, apical five chamber; IVC, inferior vena cava; LVOT, left ventricular outflow tract; SVC, superior vena cava; TOE, transoesophageal echocardiography; VExUS, venous excess congestion study; VTI, velocity time integral. ∗IVC distensibility index=([maximum diameter on inspiration–minimum diameter on expiration]/minimum diameter on expiration).

Technique	Potential clinical applications	Potential pitfalls
Inferior vena cava	• Potentially useful in extremes • Small IVC <1.5 cm with high respiratory variability >50% may suggest fluid responsiveness • Large IVC >2.5 cm with low respiratory variability <50% may suggest potential congestion • Distensibility index >18% in mechanically ventilated patients may suggest fluid responsiveness∗	•Many technical challenges and confounding factors depending on the presence of mechanical ventilation and spontaneous breathing which may not be entirely accounted for •Poor predictive value for fluid responsiveness and can often be misinterpreted
Superior vena cava	•High variability of SVC with respiration >36% may suggest fluid responsiveness	•Limited evidence suggesting superior performance compared with IVC. Requires use of TOE
Velocity time integral (VTI) at LVOT	•Well-established and validated technique that correlates with stroke volume •Significant VTI variability or significant change in VTI with leg raise or fluid bolus (500 ml) is suggestive of fluid responsiveness (typically >10% or 15%)	•Requires A5C view and appropriate alignment of LVOT with pulse wave Doppler •May be time consuming during acute resuscitation
Assessment of left ventricle	•Hyperdynamic left ventricle may suggest that additional preload may improve cardiac output •Presence of diastolic dysfunction may indicate potential for harm with excessive volumes of i.v. fluids	•Subjective and many confounding factors •Hyperdynamic LV function may be a finding of vasoplegia and not necessarily hypovolaemia
Assessment of right ventricle	•Presence of right ventricular failure may suggest increased harm with fluids	•Complex and can be subjective •Difficult to determine advanced versus chronic findings
Venous excess congestion study (VExUS)25	•Requires calculation of a VExUS score by assessing IVC distension, hepatic vein flow and pulse wave Doppler flow and intrarenal vein assessment •Based on solid physiological rationale with evidence suggesting a high congestion score predictive of acute kidney injury after cardiac surgery	•Technically difficult with poor evidence base despite physiological rationale •Further studies required in ICU patients
Lung ultrasound	•The presence of B-lines, especially with worsening when giving fluids in a pattern typical for cardiogenic pulmonary oedema may suggest harm from further fluids	•B-lines are non-specific and may be present with inflammatory and infectious aetiology

The combination of a small IVC diameter and a distensibility index (Table 5) >18% (in conjunction with a hyperdynamic LV) may be used to indicate fluid responsiveness. Unfortunately, the use of IVC diameter as a measure of fluid responsiveness has been shown to have poor predictive value in both ventilated and spontaneously breathing patients and does not reliably predict fluid responsiveness.²⁴ Advanced practitioners may find more benefit in assessing venous congestion using tools such as the venous excess ultrasound score (VExUS), to identify patients who will not benefit from additional i.v. fluids.²⁵

Severe valvular abnormalities

Severe left-sided valve lesions can be the primary cause of shock or pulmonary oedema, especially if the lesion has developed rapidly. By contrast, valvular lesions of moderate severity are unlikely to be the primary cause of shock or pulmonary oedema.

The quantification of severe valvular lesions requires advanced CCE, but qualitative identification of severe valvular abnormalities can be done quickly using basic CCE imaging. Screening for severe left-sided valvular heart disease should include visual assessment of valve morphology and interrogation of valve function with colour Doppler. Useful views include the parasternal long axis view, the apical four- and five-chamber views, and the subcostal four-chamber view. The presence of severe morphological abnormalities of the aortic or mitral valves (e.g. vegetations, flail leaflets, severe thickening or calcification, leaflet restriction) should prompt advanced echocardiographic assessment, including detailed valvular evaluation with both colour and spectral Doppler imaging.

Regurgitant lesions are more common causes of acute undiagnosed shock than stenotic lesions, and can be more readily assessed without the need for spectral Doppler. Mitral regurgitation, visualised in the apical four-chamber view, showing a central jet occupying >50% of the LA or an eccentric, wall hugging jet suggest severe regurgitation. Causes of acute, severe mitral regurgitation include endocarditis or rupture of chordae or a papillary muscle. Severe aortic regurgitation can be assessed in a parasternal long axis view or an apical five-chamber view. A jet width-to-LVOT width ratio ≥65% indicates severe aortic regurgitation. Causes of acute, severe aortic regurgitation include endocarditis (with or without aortic root abscess), aortic dissection, or acute leaflet perforation.

Echocardiography during cardiac arrest

Critical care echocardiography can rapidly rule out common causes of pulseless electrical activity and confirm the presence of cardiac arrest. While a subcostal four-chamber view can yield significant information with minimal interruption of chest compressions, TOE has several distinct advantages in this scenario and can identify the cause of cardiac arrest in 25–35% of cases.¹⁹ The TOE probe can remain in position throughout cardiopulmonary resuscitation and allow confirmation of correct position and quality of chest compressions (Figs 5 and 6 online videos). Transoesophageal echocardiography also has the advantage of facilitating initiation of extracorporeal life support, should this be appropriate. Causes of cardiac arrest that can be diagnosed with echocardiography include cardiac tamponade and clot-in-transit (Fig. 7 online video).

Conclusions

Critical care echocardiography is a core competency in modern critical care medicine. Critical care echocardiography allows for rapid, safe and accurate diagnosis of patients who present with shock or who develop cardiac arrest. Findings identified on CCE have a major impact on patient management, although evidence for improved outcomes is lacking. Rapid developments in ultrasound technology mean there are numerous portable machines suitable for CCE that are TOE capable and have cardiac quantification software.

Although CCE training continues to have significant variability across different jurisdictions, the community of CCE experts is likely to continue to grow, as opportunities for advanced accreditation and training develop.

Declaration of interests

The authors declare that they have no conflicts of interest.

MCQs

The associated MCQs (to support CME/CPD activity) will be accessible at www.bjaed.org/cme/home by subscribers to BJA Education.

Biographies

Jason Cheng MD FRCPC is a senior fellow at Auckland City Hospital and an intensive care medicine specialist originally from Canada. He has a special interest in cardiothoracic intensive care, quality improvement in extracorporeal life support and the application of critical care echocardiography in resuscitation and critical care medicine.

Robert Arntfield MD FRCPC is a consultant intensivist and traumatologist at Western University where he also serves as the medical director of the Critical Care Trauma Centre. He is coauthor of the textbook: Point-of-Care Ultrasound and is director of the critical care ultrasound program and fellowship at Western University. His major interests are resuscitative ultrasound, the use of A.I. in ultrasound and applications of transoesophageal echocardiography in critical illness and cardiac arrest.

Matrix codes: 1A03, 2A04, 3C00

Appendix A. Supplementary data

The following are the Supplementary data to this article:

Video S1

Transthoracic parasternal long axis view demonstrating normal left ventricular function.

Video S2

Transthoracic parasternal long axis view demonstrating severely impaired left ventricular function.

Video S3

Transthoracic apical four-chamber view demonstrating a dilated RV with severely impaired function.

Video S4

Transthoracic parasternal short axis view demonstrating a dilated RV with severely impaired function.

Video S5

Transoesophageal mid-oesophageal long axis demonstrating suboptimal chest compressions positioned over the left ventricular outflow tract.

Video S6

Transoesophageal mid-oesophageal long axis demonstrating correctly positioned chest compressions over the left and right ventricles.

Video S7

Transthoracic apical four-chamber view after resuscitation demonstrating clot-in-transit.