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Evidence is mounting towards focused ultrasound becoming
the first and optimal diagnostic tool in acute care medicine
Titus JA Schönberger MD
Jeroen Bosch Hospital in
‘s Hertogenbosch, The Netherlands
Chairman of Ultrasound Section of Dutch Association of Emergency Physicians
Long before the birth of medical ultrasound, the use of sound was appreciated in medical practice. Avicenna, a Persian polymath, published ‘The book of Healing’ in 1027 and described the interpretation of echoes after percussing the abdomen. In the early 19th century, the art of auscultation was considered the best diagnostic tool in evaluating chest and abdominal ailments. Ultrasound has to be regarded as the ultrasonic equivalent of percussion and auscultation combined, for it too relies on translation of characteristics of sound and their interference with human tissue into possible entities.
Point-of-care ultrasound started its revolution in the 1990s when machines became compact and affordable enough to be used in acute care environments. New technologies in probe electronics and sophisticated techniques for enhancing images slowly made the disbeliever believe and with the advent of more machines dedicated to focused imaging only, came the development of protocols like the FAST (focused assessment with sonography for trauma) protocol in 1999, through which a surgeon could reliably diagnose free abdominal fluid at the bedside.1 Since then more comprehensive protocols have been developed, such as the ACES, RUSH, FEEL, BLUE and WINFOCUS protocols. The coming of age of point-of-care ultrasound has led to the implementation in residency programmes and into the founding of dedicated training institutes and governmental installations to mitigate proper and safe use of ultrasound by physicians.
Confirmed in recent literature, incorporation of ultrasound performed by a clinician is considered best medical practice in acute care.2–4 As this is commonly appreciated in leading countries like the US, Canada, the UK and Australia, in other countries with top ranking healthcare systems, like The Netherlands, the majority of hospitals do not incorporate clinician-performed ultrasound imaging in acute care and possibly withhold their patients from best evidence healthcare.
This article will provide an overview of recent developments in point-of-care ultrasound, along with its indications, benefits and limitations. It will focus on acute cardiac and pulmonary pathologies.
Definition of point-of-care ultrasound
Focused ultrasound, bedside ultrasound, clinician-performed ultrasound, point-of-care ultrasound all denominate the same concept: the treating physician uses ultrasound imaging at the bedside to answer predefined, clinically relevant and mostly dichotomous questions. This information, together with clinical signs and symptoms, is then directly processed into diagnostic or therapeutic work-up. The learning curve of this ultrasound technique is steep and training can easily be integrated into daily practice.3 The general high accuracy of point-of-care ultrasound will shorten diagnostic processes5 and safeguard complex procedures to improve overall quality of acute care.3 Point-of-care ultrasound can easily be repeated for reassessing a patient over time or after an intervention, making it the ideal instrument for follow-up.
The main limitations of this type of ultrasound are its focused principle and its user dependency.3,4 By focusing on predefined abnormalities, comprehensive structural assessments are omitted and relevant findings could be missed. Furthermore, the user dependency of ultrasound may yield a different outcome per clinician. This variance in operator expertise must be reduced through competency certification by official institutions and by determining proper indications to reduce false positive findings, which lead to unnecessary testing, interventions and higher expenses without benefit.3,4
Aggressive diagnostics and rapid initial treatment in circulatory failure not only leads to higher quality of care, it increases survival.6 Determination of volume status is a first priority in shock, for differentiation between hypovolaemic types of shock, like septic or haemorrhagic shock, and other types of shock like cardiogenic shock with a relative plethora of blood volume, will direct appropriate treatment protocols.
In assessing circulatory failure, ultrasound provides information by interpreting physiologic characteristics of the inferior vena cava (IVC) in combination with ventricular function assessment. The determinants of the IVC are diameter and collapsibility. A wide IVC without collapsibility is indicative for obstructive or cardiogenic shock and an empty or near complete collapsing caval vein flags hypovolaemic shock and prompts immediate administration of fluids, provided overall ventricular function is adequate.
Determination of left ventricular function (LVF) can indicate the severity of left sided heart failure, if present, and can lower the threshold for administrating fluids in subclinical intravascular hypovolaemic patients. A hypotensive patient displaying normal LVF can safely cope with more intravenous fluids, while a depressed LVF calls for vasoactive or inotropic agents instead. The finding of a normal LVF with a normal IVC in hypotensive patients should direct clinical attention to other types of shock.
To provide the sonographer with some tools, many ultrasound protocols have been developed, of which the RUSH, ACES and EGLS protocols are best known. These protocols try to answer key questions, with information obtained by scanning thoracic and abdominal structures with or without scanning the lower extremities for deep venous thrombosis.
The ACES exam (abdominal and cardiac evaluation with sonography in shock) was published by Atkinson in 2009.7 This exam starts with identifying hypovolaemia by scanning the IVC and assessing LVF and then aims to identify other possible causes like abdominal aneurysm, cardiac tamponade or pulmonary embolism. Both pleural sinuses are evaluated for fluid; the lung itself is not in their equation.
The RUSH exam (rapid ultrasound for shock) was conceptualised by Weingart in 2009, published in 2010 by Perera and updated by Seif in 2012.8 It uses a plumbing concept to evaluate ‘the pump’ (pericardial effusion, right ventricular size and LVF), ‘the tank’ (estimation of IVC and complete FAST exam, along with pleural sinus and lung imaging) and ‘the pipes’ (estimation of abdominal aortic diameter and assessing deep vein thrombosis). The EGLS protocol (echo guided life support), published in 2011, combines thoracic and abdominal views and is structured around identification of one type of shock at a time, thereby possibly reducing unnecessary and time consuming additional scanning.9
Once merely regarded as the airbags of the heart and as a hindrance for proper cardiac ultrasound, lung ultrasound has surpassed the chest X-ray as the standard tool in identifying acute pathologies like pneumothorax, haematothorax and acute congestive heart failure. Bilateral comparison of ultrasound artefact patterns produced by pulmonary or extra pulmonary air pockets interacting with interstitial fluid and/or pleural fluid collections represent the most likely causes of acute dyspnoea.
In 2008, the Lichtenstein group developed the BLUE protocol (bedside lung ultrasound in emergencies), in which only sonographic findings, like the presence or absence of the lung sliding sign and unilateral or bilateral A-lines or B-lines are used to provide the most likely diagnosis of respiratory failure.5
Over the years, various authors proposed different techniques, approaches and utilities for lung ultrasound in both trauma and non-trauma settings and all used their own nomenclature. In 2012, these differences stimulated a panel of international ultrasound experts to publish a unified approach and language in lung ultrasound, shouldered by a high level of evidence.10
They stated that lung ultrasound is better than supine chest X-ray in both ruling in and ruling out pneumothorax in trauma and non-trauma settings. Other statements included the use of B-line distribution patterns in ruling in or out various pulmonary and non-pulmonary causes of dyspnoea.
For instance, unilateral presence of multiple B-lines is more indicative for pulmonary diseases like pneumonia, lung contusion, lung infarction or pleural diseases, whereas bilateral presence of B-lines with homogenous dispersal is more indicative for congestive heart failure instead. They also stated that ultrasound is more accurate than conventional radiography in detecting pleural effusion and that in case opacities are seen on chest X-ray imaging, lung ultrasound can accurately distinguish between effusion and consolidation.
Use of ultrasound in suspected pulmonary embolism (PE) in haemodynamically stable patients is limited. Ultrasound findings like signs of right heart strain and a wide IVC are inconclusive for diagnosing PE and may be caused by other conditions. In institutions without direct access to CT scanning (or if CT scanning is contraindicated) the clinician can still legitimately diagnose PE by combining cardiac and lung ultrasound with clinical gestalt, mainly by excluding other pathologies. Equally important to note is that the absence of abnormal findings on cardiac and pulmonary ultrasound cannot safely exclude pulmonary embolism.2
Despite improvements in emergency care, the chance of surviving an out of hospital cardiac arrest (OHCA) is minimal. Identifying treatable causes as early as possible remains a cornerstone in any OHCA algorithm. Without the use of ultrasound, only a few reversible causes can be identified and interventions are often withheld until clinical suspicion has become clinical certainty.
Focused ultrasound during resuscitation can identify more elusive pathologies, like cardiac tamponade or severe hypovolaemia and can drive swift intervention. A pulmonary embolism itself can only sporadically be identified by ultrasound, when visualised in the pulmonary artery or right sided in the heart, but a confirmed DVT or an severely enlarged right ventricle should instigate thrombolytic therapy.
Ultrasound can particularly be of assistance in pulseless electrical activity (PEA) protocols, for it is the only bedside tool to differentiate between pseudo PEA and genuine PEA. In both PEA subsets, a carotid artery pulse cannot be felt, either due to absent cardiac output or a physician’s failure to feel a pulse. True PEA is the absence of myocardial activity despite electrical activity by the cardiac conduction system.
In pseudo PEA however, there are organised ventricular contractions with subsequent valvular motion, but with insufficient cardiac output to achieve a palpable return of spontaneous circulation (ROSC). This situation is possibly better targeted with vasopressor and inotropic support and not with continuing chest compressions and epinephrine administration. Even so, ultrasound can distinguish between true asystole and fine line ventricular fibrillation.
Another issue in cardiac arrest is whether to continue or withhold resuscitation efforts. Normally resuscitation is halted when interventions aren’t fruitful and the efficacy of continuation is outweighed by the likelihood of poor neurologic recovery. Unfortunately, there are no algorithms for best evidence published on how and when to make this termination call.
Blaivas in 2001 and Salen in 2005 showed that ultrasound evaluation of ventricular walls and valves can adequately predict outcome of resuscitation.11,12 The presence of myocardial activity with valvular motions improves the likelihood for ROSC. Conversely, the absence of any cardiac activity correlates near perfectly with unsuccessful resuscitation and may herald the end of life.
Their results were validated by other studies, advocating ultrasound as an objective referee for determining the chance of ROSC and justifying the termination of resuscitation efforts. Exemplary protocols are the CAUSE (cardiac arrest ultrasound exam) approach by Hernandez and the FEER (focused echocardiographic evaluation in resuscitation) by Breitkreuz; both were published in 2007.13,14
There is no doubt that medical ultrasound will develop and mature to become as normal tomorrow as the electrocardiogram is today. Medical and technical pioneers will develop the next breakthrough in point-of-care ultrasound. Through univocal communication on a global level and by organising dedicated conferences on point-of-care ultrasound, any advancement will rapidly take effect to optimise the quality of care.
The real challenge for future point-of-care ultrasound users is to define optimal timing and technique of imaging, to determine proper training and credentialing and to encourage effective use by structuring hospital policy and financial reimbursements.
Since this year the International Space Station has its own ultrasound machine for use in medical emergencies, making point-of-care ultrasound the first medical imaging modality in outer space. If humans ever settle on the moon or a remote planet, the attending physician will have an ultrasound machine as their personal assistant.
Percussion and auscultation have been the tools with which physicians exercised acute care for over centuries. It was not until 20 years ago that the ultrasonic equivalent was finally deemed ready and point-of-care ultrasound was born. To provide better diagnostic tools, numerous protocols on point-of-care ultrasound have been developed and published. Through implementation of these protocols, emergency ultrasound examinations performed by the treating physician at the bedside is becoming the new gold standard in acute patient care. First the erlenmeyer flask, next the stethoscope, and now a handheld ultrasound machine is what truly depicts an acute care physician.