LET’S TALK ABOUT POCUS
By Cristina D’Alessandro
Portable ultrasound is a burgeoning technol-ogy with unrealized potential at a critical point in its evolution 1. Now reaching its “tipping point” it is being rapidly assimilated into many medical specialties beyond radiology 2. The emergence of ultrasound, especially in its hand-held porta-ble form, carries unexplored theoretical poten-tial to alter clinical decision-making, improve time to perioperative care and enhance triage 1-3. Francis Galton first generated ultrasound
waves in 1876, however it wasn’t until 1940 that ultrasound was first applied to clini-cal medicine 3. Although diagnostic medical ultrasound has been widely incorporated into emergency departments since the early 1980s, machine size and cost limited its use to the hospital arena4. The first emergency ultrasound curriculum was introduced by Mateer et al in 1994, and has since entered the core curriculum required for residency in emergency medicine 2. It is now the responsibility of each discipline to tailor the utility of ultrasound to the unique, constantly evolving demands of our individual work ecosystems.
Also termed hand-carried ultrasound (HCU) or portable trans-thoracic echocar-diography (pTTE), miniaturized ultrasound is noninvasive and cost-conscious, providing high quality visualization of anatomic struc-tures without exposing patients to harmful radiation 1,5. Differing greatly from radiologic ultrasound, POCUS (point-of-care ultrasound) aims to answer a predetermined question with a ‘yes’ or a ‘no’ answer. For example, “Is the cause of my patient’s acute dyspnea the result of pericardial effusion?” 1. Described elsewhere as problem-oriented ultrasound, POCUS is now in the hands of non-cardiologist and non-ra-diologist users such as emergency physicians, internal medicine residents, sonographers, nurses, respiratory therapists and paramedics 4.
Figure 1 illustrates some of the ultrasound devices currently available for commercial retail. Miniaturized ultrasound software is now compatible with Apple devices and they may not cost more than the iPhone in your jacket pocket or purse.
POCUS in EMS, Can We Take A Clue?
The need for quick, qualitative assessments in cardiorespiratory status are of paramount importance in prehospital care, especially since cardiac and pulmonary pathologies are often clinically very interwoven. Could a quick two- dimensional “look under the hood” at the heart and lungs provide a valuable mechanical lens to assess cardiopulmonary states? A much less talked about ultrasound exam I would like to bring to your attention is called CLUE (cardio-pulmonary limited ultrasound examination) 5. The CLUE protocol searches for signs of left ventricular systolic dysfunction, right ventricu-lar enlargement, pulmonary edema, pleural and pericardial effusions and elevation of central venous pressure in approximately two minutes 5,7.
CLUE is one example of an ultrasound augmented physical exam that could one day be tailored and transferred to paramedic practice. CLUE utilizes four views the parasternal long axis, antero-apical and postero-lateral base views of the lung, and the subcostal 4-chamber view of the heart (Figure 2) 5, 7. Using a standard 2-3 MHz ultrasound transducer, sequential imaging is captured starting from the left ventricle (LV) to the left atrium (LA) to the lungs and back to the heart through the right ventri-cle (RV) and finally to the inferior vena cava (IVC) (Figure 2) 7. Working backwards against blood flow, the CLUE exam enables the user to potentially detect a myriad of clinically signif-icant pathologies, such as cardiac tamponade, cardiogenic pulmonary edema and differentiate between septic or hypovolemic shock 7. Novice internal medicine residents have successfully utilized the CLUE protocol after brief training periods ranging between two hours to four days in duration 5. The CLUE exam has yet to be studied with working paramedics or paramedic students, therefore the feasibility of translation of this exam to the paramedic world is still unknown.
CLUE protocol, hand position, normal vs. abnormal findings. The six CLUE signs and seven hand positions and probe sites are shown with resultant views when the sign is absent (normal) or present (abnormal). Longitudinal images are oriented with cranial to the right. LAE indicates LA enlargement and RVE denotes RV enlargement. 7
Prehospital adoption of CLUE would likely be an abbreviated version of what is performed by internal medicine residents with focus on more frequently seen pathologies such as pneumo-nia, pleural effusion, pulmonary embolism and cardiogenic pulmonary edema. Pneumonia in particular, has phenomenal potential for insertion into community paramedic scope of practice, since antibiotics for pneumonia are a new line of treatment paramedics are beginning to offer. A 2014 study on pocket ultrasound’s ability to distinguish causes of dyspnea found that novice sonographers were able to diagnose pneumonia after only two 90-minute training sessions 5,9. In many studies, lung auscultation has outperformed conventional diagnostic testing such as X-ray 5,8. In 2015, a prospective study published in the Ameri-can Journal of Emergency Medicine compared the accuracy of lung ultrasound and chest X-ray utilizing CT (computed tomography) as a golden standard 5,8. Findings revealed lung ultrasound to have significantly better sensitivity of 82 per cent when compared with 64 per cent for chest X-ray, and specificity was 94 per cent for ultrasound when compared to 90 per cent for X-ray 5,8. X-rays are costly, they expose patients to harmful radiation and they involve significant time delays, thus contrib-ute to overcrowding of emergency departments. Portable ultrasound could be a more cost and time efficient solution for the detection of pneumonia, holding the potential to replace more conven-tional radiologic testing in certain clinical scenarios involving broncho-pulmonary pathologies.
Similarly, in the detection of pulmonary edema, the detection of sonographic B Lines (also known as comet tail artifact) with ultrasound outperformed X-rays5. B Lines are produced from the reverberation of sound waves against the pleura due to widening of inter-lobar septa due to the presence of fluid, fibrosis and inflammation 5 (Figure 4). B Lines are the sonographic form of rales. There must be three B lines for a comet tail to be deemed present 5. B Lines differ from A Lines, which are repeating horizontal lines seen in normally aerated lungs (Figure 3) 5. If paramed-ics performed cardiac and lung ultrasound at the scene, the health care system has the potential to be saving costs spent on X-rays. Regardless if heart and lung auscultation could affect management, having the technology at our disposal would allow paramedics to be better clinical detectives, which theoretically could enhance triage and improve patient outcome.
This view shows two ribs with posterior shadows flanking a pleural line with horizon-tal line artifacts repeating towards the bottom of the image. These A lines are observed with normal aerated lung.
This view shows two ribs with posterior shadows flanking a pleural line with comet tail-like artifacts starting at the pleura and extending to the bottom of the image. More than 3 per intercostal space can be seen. These B lines are observed with interstitial thickening, as occurs with pulmonary edema. 5
Looking Forward: Gaze at a POCUS Horizon
POCUS is not yet a standard of care in the prehospital arena. Enhancing diagnostic and monitoring capabilities with a noninva-sive, cost-effective tool could certainly prove advantageous, especially in the department of heart and lung assessments. The portability of POCUS, its diagnostic potency and ease of use are well-suited features for translation to the austere environment of prehospital care. The potential for widespread implementation of POCUS into paramedic toolkits must be spurred by evidence not enthusiasm derived from uncritical acceptance of technology 5. However, sufficient evidence suggesting ultra-sound use by paramedics can improve patient outcome has yet to be generated 2. Optimal length and modality of training and a standard-ized curriculum for training is under review with only anecdotal evidence thus far. It is up to each discipline with in-depth knowledge of workflow and particulars of work ecosystem to devise pilot studies that will inform research and practice. In the interim, let’s ease up on our investment in the “end-game”. The spirit of research is one of inquisition and uncertainty; we cannot know what is on the other side of the tunnel until we start digging. Answering the tough clinical questions that are so shamelessly asked is impossible to answer from where we stand today, shovel in hand, sweat dripping from each eyebrow. To bake the paramedic POCUS cake we must start at taking a sober look at just one crumb, then build each layer slowly and along the way decide if the benefit is greater than the temporal and financial investment. The question now is, which paramedic services and base hospitals will embrace the risk-taking spirit of research and have the boldness and courage to partake in the paramedic POCUS dig?
1 Kimura et al. Hospitalist Use of Hand-Carried Ultrasound: Preparing for Battle. Journal of Hospital Medicine 2010; 5: 163-167.
2 Jain A, Stead L and Decker W. Ultrasound in emergency medicine: a colourful future in black and white. International Journal of Emergency Medicine 2008; 251-252.
3 Liao S-F et al, Top-cited publications on point of care ultrasound:The evolution of research trends, American Journal of Emergency Medicine (2018), https://doi.org/10.1016/j.ajem.2018.01.002.
4 Nelson B and Chason K. Use of ultrasound by emergency medical services: A review. International Journal of Emergency Medicine 2008; 1: 253-259.
5 Bornemann P et al. Point-of-care ultrasound: Coming soon to primary care? Journal of Family Practice 2018; 67:70-80.
6 Rudolph S, Sorensen M, Svane C, Hesselfeldt R and Steinmetz J. Effect of pre-hospital ultrasound on clinical outcomes of non-trauma patients- A systematic review. Resuscitation 2014; 21-30.
- Kimura et al. Cardiac Limited Ultrasound Examination Techniques to Augment the Bedside Cardiac Physical Examination. Journal of Ultrasound Medicine 2015: 34; 1683-1690.
8 Nazerian P, Volpicella G, Vanni G, Vanni S et al. Accuracy of lung ultrasound for the diagnosis of consolidations when compared to chest computed tomograph. American Journal of Emergency Medicine 2015;22:620-625.
9 Filopei J, Siedenburg H, Rattner P et al. Impact of pocket ultrasound use by internal medicine housestaff in the diagnosis of dyspnea. Journal of Hospital Medicine. 2014; 9:594-597.
ABOUT THE AUTHOR
Cristina D’Alessandro is a primary care paramedic with a background in women’s studies and cardiovascular physiology. She is an advocate for optimizing cardiovascular care in EMS with research interests that include handheld cardiac ultrasound and the detection of regional wall motion abnormalities. Cristina believes that every health care provider needs a gentle reminder that women’s health issues are not just women’s problems, but rather a burden everyone shares.