Past and Present of Point-of-Care Ultrasound (PoCUS): A Narrative Review

This article aims to conduct a literature review to gain insight into point-of-care ultrasound (PoCUS). PoCUS is a rapid, accurate, non-invasive, and radiation-free imaging modality that can be used in stable and unstable patients. PoCUS can be performed parallel to physical examination, resuscitation, and stabilization; repeated exams in critical patients are essential for improving sensitivity. The review highlights how PoCUS, which was initially used to detect free intraperitoneal fluid in trauma patients, has developed into a life-saving diagnostic tool that could be utilized by treating physicians during various stages of diagnosis, resuscitation, operation, and postoperative critical care when managing sick patients. The review also notes the barriers to the widespread uptake of PoCUS in general internal medicine and the recent commercial availability of "pocket" or handheld probes that have made PoCUS more readily available. This review concludes that adopting a focused binary decision-making approach can maximize PoCUS's value in many clinical settings, including emergency departments, intensive care units, and operation theatres. Overall, the review emphasizes the importance of awareness of common indications, limitations, and strengths of this evolving and promising technology to determine its future trajectory: Providing comprehensive PoCUS training within internal medicine curriculums and supporting trainers to do so.


Introduction And Background
Over the last decade, ultrasound imaging and information systems have become sophisticated and digital, improving accessibility and affordability for ultrasound examinations.The ultrasound equipment for emergency care has become more versatile, portable, reduced in size, and predominant for better patient outcomes.This evolution allows us to do instant reporting via wireless connectivity over the electronic medical records (EMR) and picture archiving and communication system.These new devices are currently being evaluated in various clinical settings and more diverse situations that were not previously possible [1].
Point-of-care ultrasound (PoCUS) is a rapid, repeatable, accurate, inexpensive, non-invasive, and radiationfree imaging technique used in stable and unstable patients.It may also be performed parallel to physical examination, resuscitation, and stabilization.Performing repeated ultrasound exams in critical patients is essential and improves its overall sensitivity [2].The use of PoCUS by non-radiologists has developed over time.Initially, it was used to detect free intraperitoneal fluid in multiple trauma patients and was termed focused assessment sonography of trauma [3].In non-radiologists's hands, PoCUS developed into a lifesaving diagnostic tool physicians use at all levels of patient care, including diagnosis, resuscitation, operation, and postoperative critical care.Today, there is enough evidence to show that PoCUS is an effective diagnosis tool, even for non-radiologists [3].The consensus-based recommendations by the Canadian Internal Medicine Ultrasound group provided a framework for training programs at a national level with four and seven PoCUS applications and three and four ultrasound-guided procedures for PGY 1-3 and PGY 4-5, respectively [4].
PoCUS is a study that allows for the evaluation of shock status and is also an on-the-spot clinical decision tool that facilitates critical decision-making in emergencies in a short amount of time.PoCUS is unique with expanding indications to study different organs in a systematic approach at the same time and thus can be an extension of the clinical examination.For example, a simple, dichotomous protocol that uses a single microconvex probe without the need for advanced techniques helps diagnose acute respiratory failure [5].PoCUS is safe and repeatable, and when used by trained acute care professionals, it functions like a stethoscope.As mentioned above, these characteristics of PoCUS make it completely different from routine radiological studies [3].These advantages make PoCUS valuable in many clinical settings, including emergency departments, intensive care units (ICU), and operation theatres.With increased interest, training, and experience, PoCUS will be more prominent in diagnosing medical conditions [3].Significant barriers to the widespread uptake of PoCUS within general internal medicine remain for several reasons.Part of this is likely a lack of understanding of the evidence bases for this imaging modality.It is also likely that clinicians place undue confidence in the traditional clinical examination, which evidence suggests is often less robust than thought [6].
"Pocket, or handheld probes," currently commercially available, have made PoCUS less expensive and more accessible.Their web-based operation and internet connectivity could facilitate the introduction of on-thejob competency assessment and remote learning programs.Remote teaching and image review capabilities also promote quality assurance and reassurance without direct supervision when bridging the gap between initial PoCUS training and the development and monitoring of proficiency.These pocket probes offer low initial costs, low maintenance, and remote viewing of acquired images via a cloud-based platform.The availability of machines, portability, cost, remote viewing, and telemedicine are no longer barriers to PoCUS adoption.Through artificial intelligence (AI) and augmented reality, both novices and experts can acquire and interpret images, leading to faster diagnosis, focused clinical care, and better clinical decision-making.A recent study mentioned the importance of utilizing PoCUS in the primary healthcare system and PoCUS's positive impact on cost-effectiveness [7].These handheld ultrasound devices will be essential to implementing PoCUS in daily practice, which is no longer a possibility but a certainty.Handheld ultrasound probes are valuable because of their portability, cloud-sharing, and telemedicine capabilities.These features could improve patient care in the peri-operative period and faculty and resident PoCUS education.Physicians benefit from a pocket-sized probe that can switch from curved to linear image acquisition and low-to high-frequency imaging [8].PoCUS may yield helpful information during damage control resuscitation on the operating table after the damage control laparotomy and before transferring the patient to the ICU [9].
Experience over the last 25 years has shown that PoCUS is a handy tool when used by non-radiologists.Understanding PoCUS's limitations and adopting a focused binary decision-making approach can maximize its value to answer specific questions without going into detailed radiological studies.PoCUS has become an extension of the clinical examination [2].Evidence supports that adding PoCUS to examining selected patients leads to improved and earlier diagnosis in a hospital setting [10].While many studies have shown a positive impact of PoCUS on promoting medical care and reducing morbidity, mortality, and overall healthcare costs, its uniform implementation appears to be limited across the US healthcare system.Limitations can be attributed to various barriers, such as lack of training, resource scarcity, and low reimbursement.
Training primary care physicians and emergency care providers in general is the key to improving PoCUS use [11].With the aid of portable ultrasound devices, PoCUS has widened its scope to many subspecialties beyond critical care and emergency medicine.We reviewed the literature to understand its use in appropriate settings, subspecialties, and the COVID-19 pandemic.Awareness of the evolving and promising technology's common indications, limitations, and strengths is essential to determine the future trajectory.

Review Traditional use of ultrasound
Ultrasound is a non-invasive tool used in many ways for decades in the medical field.Diagnostic ultrasound can non-invasively produce images of internal organs inside the body, although it is ineffective in visualizing bones or tissues containing air like the lungs.However, in certain situations, it can produce images of bones (such as in fetuses or small babies) or the lungs and their lining when filled with fluid.One of its most common applications is monitoring fetal growth and development during pregnancy.Additionally, ultrasound imaging is utilized to visualize other areas such as the heart, blood vessels, eyes, thyroid, brain, breast, abdominal organs, skin, and muscles.The resulting ultrasound images can be displayed in 2D, 3D, or 4D (3D in motion) [7].A tissue's echogenicity refers to its ability to reflect or transmit US waves when surrounded by surrounding tissues.In terms of echogenicity, a structure can be classified into hyperechoic, hypoechoic, or anechoic (black on the screen) (Figure 1).A visible contrast difference will be apparent when structures with different echogenicities are in contact [12].Karl Dussik ), an Austrian neurologist, was the first physician to use ultrasound for medical imaging who attempted to depict changes in brain ventricle size secondary to tumor growth.In an early application of ultrasound technology, transducers were placed on both sides of a patient's partly submerged head [13].Ultrasound technology has many applications that benefit patients, such as fetal monitoring, joint injections, arterial line placements, and diagnosing bone joint pathology.These uses are popular due to their low cost, portability, and the fact that they do not involve radiation exposure.Moreover, advances in technology and engineering have ended the use of ultrasound beyond imaging and diagnostics, making it a viable therapeutic modality [14].

Types of devices and functionality
Traditional ultrasound devices are available in various types, including portable, compact, and consolebased models.Lightweight, maneuverable, portable, and compact devices are designed for point-of-care use.At the same time, console-based models offer advanced imaging capabilities and diagnostic accuracy and are used in various clinical settings.Table 1 mentions different types of devices and their functionality.Table 2 gives an insight into ultrasound utilization in the medical field.

Advantages Disadvantages
Portable ultrasound

Utilization spectrum of PoCUS
PoCUS has recently emerged as a technology with a wide array of uses.Being widely used in emergency rooms and diagnosing multiple medical conditions, its scope of utilization has broadened [31].A prospective clinical trial shows that PoCUS guides fluid resuscitation in critically ill patients [32].Zanobetti et al. regarded it as a reliable source of diagnosis for dyspnea in patients with cardiac and pulmonary conditions [33].A retrospective observational study proved that it helped prompt diagnosis and management changes for various conditions, aiding with the targeted medications and intervention use [34].Daily use of PoCUS in the morning rounds reduced the length of hospital stay, ICU stay, and length of mechanical ventilation in the various patients [35].The PoCUS role expanded in obstetrics and gynecology by aiding in lung pattern recognition in pregnant patients to cephalic presentations, fetal positions, and free fluid accumulations in busy medical settings [36,37].Studies by Akyol et al. and Becker et al. prove the high sensitivity of PoCUS in shoulder dislocations and mild sensitivity even in small bowel obstructions, respectively [38,39].Studies also emphasize its role in detecting ankle fractures, skin and soft tissue infections, and peritonsillar abscesses [40][41][42].Aiding in decreasing the role of CT in diagnosing acute appendicitis and effective diagnosis of neck masses in children, PoCUS's scope is widening in the field of internal medicine and various other specialties [43,44].[59].The bedside lung ultrasound in emergency (BLUE)-protocol adopted from lung ultrasound is helpful for immediate diagnosis of acute respiratory failure and for reducing the radiation doses from ICUs to the point of care.BLUE protocol also has profiles designed with 90% accuracy for diagnosing primary diseases such as pneumonia, congestive heart failure, chronic obstructive pulmonary disease, asthma, pulmonary embolism, and pneumothorax [60].In patients with COVID-19 pneumonia, lung ultrasound is a reliable alternative to thoracic CT scans [61].
According to a cohort study, the early detection of COVID-related pulmonary changes also helped to detect false positive reverse transcription polymerase chain reaction (RT-PCR) [62].PoCUS aided in assessing and managing circulatory and hypoxic pulmonary failure in the ICU [63].With an expanding scope during COVID-19, lung PoCUS emerged as an alternative and cost-effective diagnostic tool in step-ups where RT-PCR or CT chest is unavailable and can be an effective tool for DVT screening in COVID-19 patients, as explained by Brenner et al. and Galien et al. [64,65].Bedside PoCUS, apart from aiding in cardiopulmonary and thromboembolic diagnosis, and detection of false positive RT-PCR, being a rapid and cost-effective alternative in resource scare settings, also played a role in triaging patients during the evolving times of the pandemic [59,[62][63][64].Not only is PoCUS recommended to monitor the fluid removal efficacy of diuresis or renal replacement therapy, but it even aids in predicting restrictive renal index and severity of acute kidney injury in severely ill COVID-19 patients [66,67].The venous excess ultrasound (VExUS) evaluates IVC congestion and the severity of congestion in the liver, gut, and kidneys [5].VExUS grading system predicts acute kidney injury by assessing the severity of venous congestion [68].Therefore, a multi-organ PoCUS approach with other clinical and laboratory variables is also recommended in preference to X-ray and other imaging modalities in managing COVID-19 [66].PoCUS can be used for heart failure outpatient clinic volume status assessment [88].PoCUS has 73% sensitivity and 75% specificity in diagnosing left ventricular hypertrophy (LVH), thus helping to screen LVH patients or modifying antihypertensive therapeutics [89].The REASON trial on patients with pulseless electrical activity showed that PoCUS was associated with higher survival rates to admission and discharge [90].In patients with chest pain after initial EKG, PoCUS is used as a helpful adjunct to diagnose pericardial effusion, regional wall motion abnormalities, and type A aortic dissection [91].However, PoCUS has limitations in diagnosing pulmonary embolism [92].Compared to a 2D echocardiogram, PoCUS has 98% specificity but only 26% sensitivity in diagnosing right ventricular strain [93].Additionally, with the availability of new technology, images can now be shared with colleagues/specialists without timeconsuming uploads to EMR [94].

Benefits and limitations of PoCUS
PoCUS is an innovative, portable, and cost-effective solution to imaging that plays a vital role in reducing the number of clinicians and the constant need for patient transfer in in-patient settings.Thereby creating a streamlined environment [95].An improved doctor-patient relationship reported by 45% of patients increased patient trust in the physician's assessment and consultation.It helped patients become more aware of their health condition, as 85% of patients reported in a cross-sectional study that patients felt more secure, and 95% reported improved service and quality of care [96].Having played a major role in clinical practice, PoCUS demonstrates improved diagnosis and sensitivity compared to ultrasound and computed tomography for various cardiopulmonary, gastrointestinal, obstetrics, gynecological, and musculoskeletal conditions, with great specificity in COVID-19 patients.It helped integrate sonography with clinical examination and history at the bedside [62,97].
Due to the ease of use and high sensitivity, PoCUS is formally being introduced in the medical education curriculum at various programs.Helping in developing the skills of students in clerkships [97].Despite having numerous benefits, the need for standardized training availability for PoCUS and lack of enrollment, the desire to achieve competency impacts the proficiency and efficiency of healthcare workers, the knowledge gap in image interpretation, and the need for more supervision limits this technology's benefits.With only a fraction of doctors needing more confidence about their skills, according to a survey, and increasing usage of PoCUS in areas not usually recommended, such as aortic valve disease, the limitations of PoCUS are evident [98].Table 6 describes the benefits and limits of PoCUS.

Benefits Limitations
General

Future directions
The skills required for PoCUS usage and interpretation, resulting in limitations, will call for a novel standardized curriculum, supervision, and skill improvement that facilitates continuous hands-on training [99].On the other hand, the advancement of medicine and the ever-expanding use of PoCUS in various specialties will require further advancement in usage and technology to meet the demands of changing times.With the integration of AI, cloud-based databases, 5G-based tele-remote usage, and robotics, the specialized PoCUS will facilitate the field of medicine with its advanced application [100].
Tele-remote ultrasound -using modern computer and network communication to digitalize the ultrasound images to achieve image transmission and storage remotely.It allows remote interventional procedures and diagnosis through audio, video, and text synchronization.This remote system enables doctors to use their skills to control the robot remotely to perform ultrasound scans and medical diagnoses based on the scanning [101].5G technology has met the long-distance, high-bandwidth, and high-resolution requirements for remote ultrasound consultation and operation, even proving great value during the COVID-19 pandemic for evaluating lung lesions and guiding procedures.Therefore, it is a promising direction for PoCUS [101].
The expanding field of AI technology is gradually being implemented in medicine.It alleviates human burden and allows fast imaging processing, handling massive data, efficient diagnostic imaging, and standard maintenance, which are efficient ways of optimizing PoCUS US image processing, analysis, and diagnosis [102].With the convolutional neural network used by Buda et al. to develop an intelligent recommendation algorithm for the biopsy requirement of thyroid lesions, AI can play a vast role in ultrasound and PoCUS imaging [103].The cloud-based data sharing of the US system, where the collected image data through 5G technology is transmitted between the two locations and utilized for consultation and diagnosis, is an option that we can explore further together with specialty-specific PoCUS for clinicians to have a better understanding of different organ system and their hemodynamic [104,105].

Conclusions
PoCUS has emerged as a great tool, a cost-effective, portable, and efficient alternative to traditional ultrasound and CT scans.Its expanding usage beyond the emergency room into various specialties and settings played a significant role in the COVID-

- 19 -
Patients with age > 18 years; high suspicion of COVID-19 -LUS signs under evaluation were bilateral B lines, bilateral diffuse irregularities of pleural line, absence of significant pleural effusion, presence of multiple subpleural consolidations of various sizes -Echocardiography findings included E/A, deceleration time (DT), E/e left ventricular filling pressure, inferior vena cava collapsibility -PoCUS plays an essential role in the assessment and management of acute hypoxic pulmonary failure and circulatory failure in COVID-174 patients from two urban tertiary healthcare centers -Criteria under consideration included pleural irregularity, multiple discrete B lines, confluent B-lines, subpleural consolidations, and pleural effusions -Lung PoCUS is a rapid and costeffective tool and can be used as an alternative diagnostic tool in resourcelimited setups where RT-PCR or CT across the general ward and ICU -Depending upon risk factors for DVT, a lower extremity ultrasound was performed to screen for the occurrence of DVT -PoCUS helps detect DVT in COVID-19 patients; however, it cannot rule out the presence of pulmonary embolism Chen et -Two ultrasound fellowship-trained ED physicians performed IVC, focused cardiac -96 patients at ED of two academic hospitals -PoCUS discovered irregular pleural lines in 63.2% of the study population, bilateral confluence in 17.5%, and isolated B-lines in 53.1%, which were associated with a positive RT--PoCUS exam was effective and impactful in the diagnosis, admitted to COVID-19 unit -Daily LUS findings were correlated with initial chest Xray and clinical deterioration -LUS can be a valuable tool in continuously monitoring COVID-19 patients -Although an initial LUS at admission might not be able to predict ICU admission, ARDS, or death, a rapid increase in Mongodi LUS scores may be suggestive of lung parenchymalin an urban, academic, Level I ED with predefined signs and symptoms suggestive of COVID-19 for LUS -LUS was found to be more radiologically sensitive than chest xray to diagnose viral/atypical pneumonia -Although LUS and chest X-ray both have low specificity, PoCUS can become a practical first--19 patients in ICU -Echocardiography was performed on the day of admission, then on day three and day seven -Patients admitted for acute myocardial infarction or pulmonary embolism with a positive COVID-19 PCR swab test were excluded from study -Ejection fraction for left ventricle (LVEF) and Left ventricular GLS are equivocally effective in assessing left ventricular systolic function -Right ventricular GLS weakly correlated with fractional area change (FAC), tricuspid annular plane systolic excursion (TAPSE) and not correlated in any way with tissue Doppler velocity of the basal free lateral wall (S') for the right -19 inpatients; a baseline LUZ score was established with primary endpoints being inhospital death and/ or admission to ICU -Secondary outcomes like the length of hospital stay, escalation of medical treatment, and oxygen requirements were predicted using the baseline score -Baseline LUZ score was predictive of severity of infection during hospital stay and, in turn, helps in early intervention and COVID-19 inpatients of > 18 years old; non-pregnant patients with specific COVID-19 symptoms -LUS was performed within 48 hours of admission and compared with a prospective RT-PCR test -LUS scoring ranged from 0-3 in 12 lung regions bilaterally based on ultrasound findings -Patients with a score of 0 or 1 in all areas were classified as "LUS-COVIDnegative."-Patients with a score of 2 or 3 in 1 out of 12 areas were classified as "LUS-COVIDpositive."-PPV and NPV of LUS were assessed to be 34.1% and 97.1% -Significantly higher NPV of LUS can depict its importance in ruling out COVID-19 infection -107 ICU COVID-19-positive patients confirmed 2023 Chelikam et al.Cureus 15(12): e50155.DOI 10.7759/cureus.PCR -The "2-region technique" was implemented for the diagnosis of DVT in the lower extremity, which involved compression of 1-2 cm area proximally and distally to (i) junction of great saphenous vein and common femoral vein extending to the confluence of superficial and deep femoral vein, (ii) posterior aspect of knee extending from proximal popliteal vein to confluence of calf vein -PoCUS diagnosed 15.9% lower extremity DVT on Day 1, 6% on Day

Table 3
gives an insight into PoCUS utilization in the medical field.

name, year Study type PoCUS use Study details/outcome Conclusion
ED physicians completed the study -All correctly identified the absence of tablets in bags containing only water -Diagnosed the presence of ECA tablets in bags containing water and PEG -For Part 2 of the study, most participants -67.5% (25/37) using water, (62.1%) 23/37 using PEG, and all 100% (37) using activated charcoal -underestimated the number of ECA pills in solution by at least 50% -Potential role of PoCUS in evaluating suspected acute, massive overdose in patients.

ultrasound PoCUS use during COVID-19 pandemic Multi
-organ PoCUS, with other imaging and diagnostic modalities, played a significant role in triage, diagnosis, and management of COVID-19 patients.The prospective study by Alharthy et al. explains that PoCUS helped detect various pulmonary changes, such as B lines and pleural lines, in ICU-bound patients with deep venous thrombosis (DVT)

Table 4
explains the emerging role of PoCUS in the COVID-19 pandemic.

TABLE 6 : List of benefits and limitations of PoCUS
PoCUS: Point-of-care ultrasound 19 pandemic.By assisting in remote and onsite COVID-19 diagnosis, PoCUS has gained considerable space in medical school and training program curriculums.Despite having a few limitations due to a lack of standardized training, the emerging technological advancements in AI, 5G communication, and cloud-based sharing are promising futuristic directions for PoCUS imaging and medical diagnosis.