Should Point-of-Care Ultrasound Examination Be Routine Practice in the Evaluation of the Acutely Breathless Patient? No
COUNTERPOINT: Should Point-of-Care Ultrasound Examination Be Routine Practice in the Evaluation of the Acutely Breathless Patient? No
Patients with acute breathlessness who are admitted on an emergency basis to hospital represent a significant and recurring challenge. These patients are frequently frail and comorbid with overlapping pathologies, each of which may potentially offer an explanation for their symptoms. This can lead to initial investigation and treatment that is directed at all possibilities in the face of diagnostic uncertainty, with the risks of treatment complications and poor outcomes in a population with limited physiologic reserve.1, 2 Point-of-care ultrasound (POCUS) has been heralded as a solution to this clinical conundrum, providing an accessible bedside investigation that can rapidly differentiate between the most common disease processes and guide subsequent treatment.
However, incorporating any investigation or intervention into routine practice requires robust evidence showing how and when it should be used and its positive impact on clinical care, improving hard measurable outcomes that both clinicians and patients are interested in. These outcomes may include a reduction in patient morbidity and mortality; or in the use of health-care resources such as other diagnostic tests and hospital bed days. It is this crucial detail that is largely absent from the evidence base for the use of POCUS in the acutely breathless patient, and which means it cannot be regarded yet as a standard of care in this population.
The international consensus statement on point-of-care lung ultrasound3 provides a thorough overview of the core evidence base that has underpinned this area of clinical practice over the past few years. Many of the cited articles have been conducted as diagnostic accuracy studies and have methodical limitations such as patient selection or choice of reference test. Furthermore, these same studies have largely been carried out in highly selected patient populations and/or specific clinical environments that raise concern as to whether the findings are truly generalizable or reproducible elsewhere. For example, evidence relating to the use of lung ultrasound to diagnose pneumothorax is almost entirely derived from trauma, critical care, and postprocedural patients. This population has a far higher prevalence of pneumothorax than would be seen in an unselected cohort of acutely breathless patients, meaning ease of sonographic detection and diagnostic reliability in the latter group remain uncertain.4, 5
One of the most widely cited studies relating to the use of POCUS in patients with respiratory failure6 was conducted retrospectively and excluded individuals with either uncertain or multiple diagnoses from the final statistical analysis, with the inevitable result being that the outcome data look better than they might otherwise have, had these more challenging cases been included. Indeed, in many similar studies in this area of practice the choice of reference test has been limited to final discharge summary or a retrospective case notes review, which in themselves may not be either consistent or accurate. A systematic review7 addressing the identification of lung consolidation and pneumonia by ultrasound commented on the limitations of the evidence base relating to this common diagnosis, and in particular the shortage of studies where CT imaging had been utilized as a “gold standard” radiologic test for comparison. If there is a diagnostic advantage from using POCUS in the unselected patient population with acute breathlessness, it remains unclear where this is and whether it is relevant in the longer term. A large randomized study8 using POCUS in an unselected ED population saw the greatest gains in the confident diagnosis of heart failure and pleural effusions; there were less significant positive changes in other common diagnoses, and no impact on longer-term outcomes such as length of hospital stay or mortality.
Almost all studies cited by the consensus statement3 have been delivered by small numbers of experts, both in terms of experience with POCUS but also their clinical seniority and, by extension, knowledge. This means the data presented either are, or are close to, the best expected in terms of diagnostic sensitivity and specificity. There are few, if any data demonstrating what diagnostic gain can be achieved with the use of POCUS in nonexpert hands. This is important since POCUS is an extension of the stethoscope and clinical examination, rather than a truly stand-alone diagnostic test. Many of the findings on lung ultrasound may be caused by a range of pathologies, all of which can result in acute breathlessness. As such, apart from being able to perform POCUS the clinician must be able to assess and integrate the sonographic data with any other available clinical information to come to a working diagnosis and treatment plan. This leaves POCUS in the breathless patient vulnerable to the skill of the operator in acquiring and interpreting ultrasound images, as well as to their clinical judgment and ability to use this additional information to actually inform the diagnosis and not simply succumb to confirmation bias. Furthermore, if POCUS is to be routinely used by all physicians when assessing the acutely breathless patient, there must be clear standards with respect to training and assessment of competence, both initial and continued. A recent systematic review9 has highlighted the inconsistencies and heterogeneity in educational practice around lung ultrasound, and thereby the need to address these deficiencies before its use can be widened. A failure to do so will ensure POCUS ultimately faces the training gap that already affects chest radiograph interpretation and its value as a diagnostic tool.10, 11
Most clinicians would consider auscultation or chest radiography as fairly standardized with general consensus or protocols on how to perform the procedures. This is not the case for all forms of POCUS. In the international consensus guidelines for focused cardiac ultrasound12 some recommendations are given regarding choice of equipment, protocols, and used views, which could serve as an approach when using this technique in acutely breathless patients. The same is not true for lung ultrasound, in which there is no clear international consensus regarding choice of equipment or protocol used in a given patient group or setting. Many POCUS studies have used a focused approach in which ultrasound examination is limited to assessing predefined, binary questions. This approach has been advocated since it seems to ensure a steep learning curve and high diagnostic accuracy for even nonexperts. Based on current evidence some conditions seem reasonable to assess using a focused approach (eg, interstitial syndrome, pleural effusion) whereas others may not be so straightforward (eg, pulmonary embolism). It does not make sense to implement a technique as part of routine practice unless there is a general consensus and evidence-based approach on how to actually perform the procedure, and if a focused approach is to be used then which questions to ask? Issues around governance need to be considered at the same time; if POCUS is to become the standard of care then what is the minimum imaging data set that needs to be acquired and recorded for each patient and made available for later review if necessary?
Almost all the studies that have addressed the use of POCUS in the acutely breathless patient have focused on the accuracy of and speed with which a clinical diagnosis is made; and, to a lesser extent, the impact this has on initial treatment. There is a paucity of data to show how the use of POCUS impacts on longer-term outcomes, either clinical or health economic. The routine use of POCUS in acutely breathless patients—and there are many—will require a significant investment in terms of equipment and training at under- and postgraduate levels to ensure a widespread and responsive service in all hospitals. Diagnostic accuracy does not always translate into patient benefit,13 and an intervention or investigation that does not improve either patient morbidity (including length of hospital stay) or mortality has little worth, particularly if it does not have a proven societal or economic benefit either. The short- and long-term benefits of incorporating POCUS into routine care have been well demonstrated in other areas,14 and it is this bar that the evidence base for using POCUS in the acutely breathless patient needs to meet to be considered a clinically credible and financially viable addition to current practice.
In conclusion, there are encouraging data on the use of POCUS in breathless patients, but largely derived from highly selected populations; these data cannot justify its place as a standard of care across the hospital. POCUS undoubtedly has a role in selected locations, notably critical care environments, where the diagnostic value of alternative investigations is likely to be diminished by patient characteristics. However, larger-scale studies looking at the impact of POCUS on hard clinical outcomes such as patient morbidity and mortality in an all-comers population with acute breathlessness are now needed to better inform clinicians as to when and where this form of clinical examination is best used.