“The real benefit to the patient [of echocardiography] is not the technical skill, but rather the application of intellectual input… information, communication and teamwork are essential” Jos Roelandt, 1993
Of all the imaging techniques used in intensive care, echocardiography has come to the fore, in particular due to its accessibility, immediate availability and applicability as a point-of-care technique, thereby removing the risks of transportation of the critically ill. Over the preceding 20 years evidence has continued to emerge for its extended use in the acute/emergency setting, to the extent that it is now included in national and international guidelines relating to the universal definition of myocardial infarction, as well as in shock pathways, and as an adjunctive technique in advanced life support. Its potential scope is huge, with applications relating to monitoring, cardiac pathophysiology and coronary perfusion as well as its more evident use to define cardiac anatomy.
The three main uses of ultrasound to interrogate the heart relate to the way in which the technique is used: first, as an extension to the clinical examination using binary questions and 2D imaging only (focused cardiac ultrasound, FoCUS) which forms the basis of ‘basic’ techniques. Second, incorporating the full range of echocardiographic techniques for diagnostic capability (echocardiography), and third, selective application of the full range of techniques in order to answer specific questions raised in the critical care/emergency arena (targeted echocardiography). This includes speckle strain/strain-rate to determine abnormalities of myocardial function suggestive of myocarditis, calculation of myocardial electromechanical efficiency in order to maximise cardiac output, recognition of parameters that suggest restrictive right ventricular physiology, with the requirement for modification of ventilatory techniques and parameters, detection of myocardial ischaemia, estimation of LVEDP and LAP, and its application in the institution, monitoring and weaning of mechanical circulatory support.
Key questions for the clinician undertaking echocardiography in the critical/acute/emergency setting can be summarised in a checklist format, which includes:
- What is the clinical context?
- What does the treating clinician want to know (ie why won’t the patient wean from mechanical ventilation? or is this pulmonary oedema, and if so, why?).
- Can echocardiography answer the required question, and what is the accuracy in this setting?
- What is the underlying diagnosis (cardiac and non-cardiac)?
- How is the patient being sedated/ventilated/supported
Specific echocardiographic data:
- What is limiting the cardiac output/elevating the venous pressure?
- Is the left atrial pressure elevated?
- Is the heart rate/AV delay/VV delay appropriate?
- Is there any other relevant information that the treating clinician needs to know that may inform planned interventions?
To reach its full potential in the critical arena demands therefore not only understanding of the whole range of echocardiographic techniques, but also the confounding factors that will be found in this setting, including filling status, ventilatory parameters, mechanical support and the use of vasoactive agents. Although frequently ‘simplified’ for application in FoCUS, expert echocardiography in this setting can be extremely challenging, and the potential to cause harm to the patient through misinterpretation should not be underestimated.