Utilization of Point-of-Care Ultrasound as an Imaging Modality in the Emergency Department: A Systematic Review and Meta-Analysis

Point-of-care ultrasound (POCUS) is an imaging modality that has become a fundamental part of clinical care provided in the emergency department (ED). The applications of this tool in the ED have ranged from resuscitation, diagnosis, and therapeutic to procedure guidance. This review aims to summarize the evidence on the use of POCUS for diagnosis and procedure guidance. To achieve this, CrossRef, PubMed, Cochrane Library, Web of Science, and Google Scholar databases were extensively searched for studies published between January 2000 and November 2023. Additionally, the risk of bias assessment was performed using the Quality Assessment of Diagnostic Accuracy Studies 2 (for studies on the diagnostic role of POCUS) and Cochrane Risk of Bias tool (for studies on the use of POCUS for procedure guidance). Furthermore, diagnostic accuracy outcomes were pooled using STATA 16 software (StatCorp., College Station, TX, USA), while outcomes related to procedure guidance were pooled using the Review Manager software. The study included 81 articles (74 evaluating the diagnostic application of POCUS and seven evaluating the use of POCUS in guiding clinical procedures). In our findings sensitivities and specificities for various conditions were as follows: appendicitis, 65% and 89%; hydronephrosis, 82% and 74%; small bowel obstruction, 93% and 82%; cholecystitis, 75% and 96%; retinal detachment, 94% and 91%; abscess, 95% and 85%; foreign bodies, 67% and 97%; clavicle fractures, 93% and 94%; distal forearm fractures, 97% and 94%; metacarpal fractures, 94% and 92%; skull fractures, 91% and 97%; and pleural effusion, 91% and 97%. A subgroup analysis of data from 11 studies also showed that the two-point POCUS has a sensitivity and specificity of 89% and 96%, while the three-point POCUS is 87% sensitive and 92% specific in the diagnosis of deep vein thrombosis. In addition, the analyses showed that ultrasound guidance significantly increases the overall success rate of peripheral venous access (p = 0.02) and significantly reduces the number of skin punctures (p = 0.01) compared to conventional methods. In conclusion, POCUS can be used in the ED to diagnose a wide range of clinical conditions accurately. Furthermore, it can be used to guide peripheral venous access and central venous catheter insertion.


Introduction And Background
Ultrasound is a technology employed in various medical fields, including obstetrics, cardiology, critical care, emergency medicine, pediatrics, and primary care.In recent years, ultrasound technology has evolved from large immobile machines to portable devices on wheeled carts and currently to handheld devices capable of fitting in the clinician's pocket [1].Point-of-care ultrasound (POCUS) is primarily used to complement physical examination.It is gaining attention because it can enable disease screening, accelerate definitive diagnosis, guide clinical decision-making, and decrease overall healthcare expenses [2][3][4][5].Currently, there are many POCUS devices in the healthcare field, with research suggesting that these devices are highly accurate when employed by trained personnel and often rival or surpass other imaging modalities [6][7][8].
According to the American College of Emergency Physicians, the use of POCUS in emergency medicine is categorized into five clinical categories, i.e., resuscitative, diagnostic, symptom or sign-based, procedure guidance, and therapeutic [9].In resuscitation, POCUS has been reported to serve as a prognostic tool in cardiac arrest, where physical examination is not always accurate [10,11].In addition, POCUS can aid in the rapid determination of the underlying causes of undifferentiated shock, allowing for targeted and effective resuscitation efforts.As a diagnostic tool, POCUS is versatile as it can help healthcare providers evaluate various organ systems at the patients' bedside.Furthermore, it has proven effective in enhancing safe and accurate invasive procedures within the emergency department (ED).These procedures vary from central venous placement and draining abscess to assisting regional nerve blocks [12,13].
Although POCUS has a wide range of applications in the ED, we decided to focus on the following applications: the use of POCUS in diagnosing various clinical conditions and guiding clinical procedures.

Information Sources and Searches
The CrossRef, PubMed, Cochrane Library, Web of Science, and Google Scholar databases were extensively searched for primary studies published between January 2000 and November 2023.In addition, the bibliographies of potential studies were reviewed for additional studies.The strategy employed to identify studies from the databases mentioned above was as follows: (Point-of-care ultrasound OR POCUS OR handheld ultrasound OR pocket-size ultrasound OR bedside ultrasound OR Emergency ultrasound) AND (Emergency department OR ED OR Emergency medicine OR emergency room OR emergency ward).Furthermore, all gray literature was avoided as it includes unpublished data likely to undermine the scientific purpose and statistical power of this study.

Eligibility Criteria
Two impartial reviewers analyzed the studies from the aforementioned databases, included articles if they were published in English, and evaluated the use of POCUS in the ED.On the other hand, articles that did not meet these criteria or were designed as conference abstracts, reviews, case reports, and letters to the editors were excluded.Furthermore, studies reporting the use of POCUS by prehospital emergency medical services were excluded.Any discrepancy during this process was amicably resolved via constructive debates between the two reviewers.

Data Extraction
Two independent reviewers analyzed the eligible studies and abstracted the data required for review and analysis into separate Excel files.In case of disparities in the abstracted data, the reviewers engaged in constructive discussions, and if they could not reach a compromise, a third reviewer was consulted.The data retrieved by these reviewers included author ID (surname of the primary author and year of publication), study design, pertinent characteristics of enrolled patients (sample size and sex distribution), the use of POCUS, test condition, reference/criterion standard, operators, and the outcomes.
The outcomes in our study were divided into procedural and diagnostic.The diagnostic outcomes included sensitivity and specificity, while the procedural outcomes were success rates, procedure-related complications, time to successful catheter insertion, and the average number of skin punctures.

Quality Appraisal
The methodological quality of studies in the present review was assessed using two different tools.The Quality Assessment of Diagnostic Accuracy 2 (QUADAS-2) tool embedded within the Review Manager software was used to evaluate the risk of bias in each study assessing the diagnostic role of POCUS.Using this tool, the included studies were assessed according to four bias assessment domains (patient selection, index test, reference standard, and flow and timing) and three applicability domains (patient selection, index test, and reference standard).
On the other hand, bias assessment of studies on the use of POCUS to guide procedures in the ED was done using the Cochrane Risk of Bias tool (RoB).With this tool, the risk of bias in each study was assessed according to the selection, attrition, performance, reporting, and other biases.A low risk of bias meant the criteria in each domain were sufficiently addressed, while a high risk of bias meant that the criteria were not addressed.On the other hand, an unclear risk of bias referred to the inability of reviewers to provide conclusive judgment due to insufficient information.

Data Synthesis
STATA software (StataCorp Stata MP 16.0, College Station, TX, USA) was used to pool the outcomes on the diagnostic accuracy of POCUS.On the other hand, the Review Manager software (RevMan 5.4.1) was used to pool outcomes related to the use of POCUS in guiding procedures.The DerSimonian Laird effects model was employed in all statistical analyses to calculate conservative effect sizes and counter the anticipated heterogeneity.Furthermore, the heterogeneity was calculated using the I 2 statistics, wherein values above 50% were regarded as substantial [14].For dichotomous outcomes, the effect size was calculated using the simple odds ratio (OR), and the mean difference (MD) calculations were used to pool the continuous outcomes.In cases where median, range, and interquartile ranges were presented, the formula described by Hozo and colleagues was used to calculate the means and standard deviations [15].

Study Selection
Our preliminary database search identified 4,673 viable records.The in-depth duplicate screening criteria led to the exclusion of 2,213 records regarded as exact or nearly identical duplicates.Additionally, the title and abstract screening led to the exclusion of 1,929 records.Of the remaining 531 articles, 388 were not retrieved as they were either non-full-text records, ongoing trials, conference abstracts, case reports, experimental studies, letters to the editor, or systematic reviews and meta-analyses.Finally, only 81 articles were eligible for inclusion, while the other 62 were excluded as follows: 17 were published in different languages, and 45 evaluated the prehospital use of POCUS. Figure 1

Summary of Study Characteristics
Of the 81 included studies, 74 evaluated the use of POCUS as a diagnostic tool and seven assessed the use of POCUS for procedure guidance.Furthermore, 29 reported the diagnostic utility of abdominal POCUS, five ocular POCUS, six soft tissue POCUS, 19 musculoskeletal POCUS, 11 vascular POCUS, and four lung POCUS (Table 1).

Risk of Bias Assessment
The full risk of bias assessment according to the QUADAS-2 tool is summarized in Figure 2, while the assessment according to the RoB is outlined in Figure 3.For the QUADAS scores, a high risk of bias under the patient selection was outlined when a convenience sample was used.Furthermore, studies that had more than one reference standard were regarded to have a high risk of flow and timing bias.

POCUS as a Diagnostic Tool in the ED
In this study, the diagnostic use of POCUS in the ED was categorized according to the body region.The pooled analysis showed that abdominal POCUS had a sensitivity and specificity of 65.61% and 88.86% for appendicitis, 81.74% and 74.09% for hydronephrosis, 93.15% and 81.80% for small bowel obstruction (SBO), and 74.73% and 95.56% for cholecystitis, respectively.The pooled analysis also showed that ocular POCUS was 93.66% sensitive and 90.90% specific when diagnosing retinal detachment in the ED.
In addition, our analysis suggested that soft-tissue POCUS aids in the diagnosis of abscess with a sensitivity of 94.75% and a specificity of 85.15%, and in identifying foreign bodies with a sensitivity of 66.7% and a specificity of 96.6%.Furthermore, musculoskeletal POCUS demonstrated a sensitivity and specificity of 93.11% and 94.94% for clavicle fractures, 96.76% and 94.94% for distal forearm fractures, 94.20% and 92.36% for metacarpal fractures, and 90.78% and 97.06% for skull fractures.
On the other hand, subgroup analyses on the diagnostic value of vascular POCUS showed that two-point compression POCUS diagnoses deep vein thrombosis (DVT) with a sensitivity of 88.85% and a specificity of 96.29%, while three-point compression POCUS is 86.93% sensitive and 92.41% specific.Moreover, lung POCUS aids the diagnosis of pleural effusion with a sensitivity and specificity of 90.56% and 96.81%, respectively.These pooled analyses are outlined in Table 3.

POCUS for the Guidance of Procedures in the ED
In this study, we analyzed the use of POCUS in guiding central venous insertion and peripheral venous cannulation.The pooled outcomes showed that the success rate for peripheral venous access was considerably higher when guided by POCUS compared to the traditional method (p = 0.02).However, the interstudy heterogeneity was high (80%).Similarly, the pooled analysis suggested that the number of skin punctures required for peripheral venous access was significantly less when using POCUS for guidance compared to the traditional techniques (p = 0.01).However, the heterogeneity was substantial (98%).On the other hand, our meta-analyses showed that ultrasound-guided and traditional methods of peripheral venous access are equally effective and safe, as demonstrated by the time taken to achieve successful cannulation and complication rates.
Regarding the use of POCUS to guide central venous catheter (CVC) insertion, we found no significant difference in the rate of procedure-related complications between the ultrasound-guided and traditional methods.However, one of the studies, including pediatric patients only, reported that the rate of successful CVC insertion was higher when using POCUS guidance (OR = 13.1;95% CI = 2.9-59).Similarly, Miller and colleagues reported that among patients undergoing CVC insertion, POCUS guidance significantly reduced the time to successful insertion and the number of skin punctures required compared to the landmark technique (p < 0.0001).The outcomes of POCUS as a tool guiding procedures in the ED are summarized in

Discussion
This systematic review and meta-analysis has summarized the procedural and diagnostic use of POCUS in the ED.The pooled analysis showed that in most conditions, POCUS has a high sensitivity, meaning it can help emergency physicians (EPs) rule out a condition, and for other conditions, it has high specificity, meaning it can rule in a diagnosis [97].Furthermore, our statistical analyses suggest that POCUS can improve the success rate of peripheral and central venous access and reduce the number of skin punctures compared to conventional methods.
Abdominal ultrasound is an imaging test that helps healthcare providers diagnose or rule out health conditions in the abdominal areas.In this review, we analyzed the use of abdominal POCUS in diagnosing appendicitis, hydronephrosis, SBO, and cholecystitis.Our pooled analyses showed that POCUS has a moderate sensitivity and a high specificity in diagnosing appendicitis.These findings align with what was already recorded in previous studies.Nicole and colleagues found that among pediatric patients only, POCUS had a limited sensitivity (53%) but a relatively high specificity (82%) for appendicitis [18].Similarly, Lee and Yun found that EP-performed POCUS had a higher specificity for appendicitis diagnosis than sensitivity (91% vs. 84%) [98].Considering these findings, it seems that there is inconclusive evidence on the use of POCUS to rule out appendicitis in the ED; however, POCUS has the potential to be used in ruling in this condition.
The usefulness of POCUS in diagnosing hydronephrosis was also evaluated in the present study.The pooled analyses showed that POCUS has a high sensitivity and moderate specificity for diagnosing hydronephrosis.However, the diagnostic accuracy varied from study to study.In their research, Pathan and colleagues reported that when using a CT scan as the reference standard, POCUS was highly specific (94.6%) in diagnosing moderate-to-severe hydronephrosis but had an inferior sensitivity (34.2%) [28].This finding is also witnessed in other studies where CT scans were used as the reference standard [33].On the other hand, Javaudin and colleagues found that EP without any previous POCUS skills can rule out hydronephrosis in the ED with satisfactory sensitivity (100%) [31].This contradictory information suggests that there is still a gap in the use of POCUS to diagnose hydronephrosis in the ED, and more randomized trials are required.However, the contradiction observed can be related to the fact that Jauvadin and colleagues used radiologist-performed ultrasound as the reference standard rather than a CT scan which is considered the gold standard imaging modality for hydronephrosis [34].
SBO symptoms are frequently observed in ED patients.Typically, the gold standard diagnosis for this condition before hospital admission is a CT scan.However, currently, the use of ultrasound at the patient's bedside has emerged as an intriguing concept.In our study, we found that POCUS had a high sensitivity and specificity for SBO, suggesting that POCUS can play a vital role in ruling out and diagnosing SBO in the ED.However, some studies have reported contradictory information.Becker and colleagues reported that although POCUS was highly sensitive (88%) for SBO, it was less specific (54%) [37].The difference cited in this study can be attributed to the fact that most of their sonographers were highly inexperienced when it came to using POCUS.Additionally, our meta-analysis showed that POCUS has moderate sensitivity but is highly specific in diagnosing cholecystitis in the ED.Therefore, our findings suggest that POCUS might be a reliable tool for ruling in cholecystitis in the ED.In the ED, patients can present with various ocular emergencies, ranging from simple conjunctivitis to sightthreatening diseases.Due to limited access to ophthalmology in some settings, these emergencies may burden the EP to make swift decisions [99].One of the common eye complications presenting to the ED is retinal detachment; therefore, it is worth noting whether POCUS may aid the EP in diagnosing this condition.Our statistical analyses found that POCUS is highly sensitive and specific when diagnosing retinal detachment in the ED.This is further reinforced by a 2019 meta-analysis that found that ocular POCUS performed by EP had a sensitivity and specificity of 94% and 91% for retinal detachment [100].Therefore, it is evident that POCUS can accurately diagnose retinal detachment in the ED.Furthermore, one of the studies reported a high sensitivity and specificity for vitreous hemorrhage (81.9% and 82.3%, respectively) and a very high specificity for vitreous detachment (96.6%) [48].

The Diagnostic Utility of
The Diagnostic Utility of Soft Tissue POCUS Skin and soft tissue infections (SSTIs) are among the most common ED complications.In our research, we found that among patients with signs of SSTI, POCUS was 95% sensitive and 85% specific in diagnosing abscesses.This finding aligns with a previous systematic review, which recorded a pooled sensitivity and specificity of 96% and 83%, respectively, for diagnosis of abscess [101].Furthermore, a 2016 meta-analysis demonstrated similar test characteristics [102].These findings suggest that among patients presenting to the ED with SSTIs, POCUS is sufficient to diagnose abscesses.In addition, data from one study indicated that POCUS can be used to rule in foreign bodies in the ED due to its high specificity [55].

The Diagnostic Utility of Musculoskeletal POCUS
Complaints about musculoskeletal pain are very common in the ED.In our study, we investigated the diagnostic accuracy of POCUS in diagnosing clavicle, distal forearm, metacarpal, and skull fractures.The analyses have shown that POCUS is highly sensitive and specific when diagnosing these musculoskeletal fractures in the ED.These findings concur with the previous studies on the use of POCUS to diagnose musculoskeletal fractures [103].Therefore, it is evident that POCUS can accurately diagnose clavicle, distal forearm, metacarpal, and skull fractures among adult and pediatric patients in the ED.Furthermore, evidence suggests that POCUS can aid in diagnosing tendon injuries such as Achilles, patellar tendons, and quadriceps in the ED [104][105][106].However, the high diagnostic accuracy of POCUS for musculoskeletal fractures does not mean that it can replace the need for subsequent X-rays but can be used as a complementary imaging tool or as an alternative in cases where X-rays are not immediately available.

The Diagnostic Utility of Vascular POCUS
DVT is a life-threatening vascular condition affecting patients of all ages.Therefore, rapid and accurate diagnosis of this condition is crucial because research has shown that one-third of DVTs that are left untreated progress to significant pulmonary embolism [107].The gold standard test for DVT is contrast venography; however, vascular POCUS is increasingly being employed in the ED to assess this condition [8,108].Currently, there are two kinds of POCUS techniques used to evaluate DVT in the lower extremities.The first technique is the two-point compression which involves testing the compressibility of the common femoral vein (CFV) and the popliteal vein (PV), and the other technique is the three-point compression which involves the compression of CFV, PV, and the superficial femoral vein (SFV).In this meta-analysis, we found that two-point and three-point POCUS techniques had similar test characteristics when evaluating DVT in the ED.These findings are corroborated by a previous meta-analysis of 2,372 patients which found that the two-point POCUS had a similar pooled sensitivity and specificity as the three-point POCUS [109].
Given that the test characteristics were high, POCUS can be used to accurately diagnose lower extremity DVT in the ED.

The Diagnostic Utility of Lung POCUS
Shortness of breath (medically known as dyspnea) and chest pain are common complaints in the ED.The initial management of these complaints can be challenging because of the differential diagnoses, which are often life-threatening conditions in need of urgent identification and management [110].Generally, a chest radiograph (CXR) is the initial diagnostic tool for patients with dyspnea and chest pain.However, previous research has shown that CXR has limited sensitivity and specificity, raising questions about its diagnostic utility [87,111].As a result, the use of POCUS in different clinical settings to assess the causes of dyspnea and chest pain is rapidly growing.In our study, we found that among dyspneic patients presenting to the ED, POCUS had a sensitivity and specificity of 91% and 97%, respectively, for the diagnosis of pleural effusion.Therefore, POCUS seems to be a feasible diagnostic tool that can narrow down the diagnosis of pleural effusion.Given the benefits of POCUS in reducing healthcare costs, enhancing fast care delivery, and radiation-free testing, our findings suggest that POCUS can be incorporated in the ED to diagnose pleural effusion in patients presenting with dyspnea and chest pain.

POCUS for Procedure Guidance in the ED
In the ED, POCUS can be used to guide several procedures; however, in this review, we investigated the use of POCUS in guiding peripheral venous and central venous access.Patients with difficult peripheral venous access usually require multiple attempts and perhaps central venous access, resulting in increased time and resource use in the ED.Therefore, it is worth studying whether ultrasound guidance may help improve peripheral venous access.In our study, we found that ultrasound guidance significantly improved the success rate and reduced the number of skin punctures during peripheral venous access compared to the traditional methods.However, the heterogeneity between studies was substantial, suggesting outcome variation.Furthermore, we found that ultrasound guidance does not reduce the time taken for successful cannulation compared to the traditional techniques.Therefore, further high-quality randomized trials are required to support the potential benefit of POCUS in guiding peripheral venous access.Similarly, evidence suggests that POCUS may be beneficial in performing CVC insertion more rapidly and in fewer attempts; however, this finding requires further investigation.

Limitations
The current study has several limitations that should be accounted for when interpreting the findings.First, we observed substantial heterogeneity in several meta-analyses.However, we used the random-effect model to counter this heterogeneity and provide conservative results.Second, we only included studies published in English from the year 2000 onward; hence, it is possible that selection bias was introduced in our research.Finally, most studies in this review were non-randomized, which might have introduced the confounding bias witnessed in such studies.

Conclusions
This systematic review and meta-analysis shows that POCUS has increasingly been utilized in the ED over the past two decades.It also indicates that POCUS in the ED can accurately diagnose clinical conditions such as SBO, retinal detachment, abscess, clavicle fractures, distal forearm fractures, metacarpal fractures, skull fractures, pleural effusion, and DVT.In addition, we have demonstrated that POCUS can aid in ruling in appendicitis, foreign bodies, and cholecystitis due to its high specificity.Furthermore, POCUS can potentially increase the success rate of peripheral vein and central venous access and decrease the number of skin punctures; however, these findings require further investigations in high-quality randomized trials.
illustrates the Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram of study selection for the systematic review.

FIGURE 1 :
FIGURE 1: Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram for study selection.

FIGURE 5 :
FIGURE 5: Point-of-care ultrasound sensitivity and specificity for hydronephrosis diagnosis.

FIGURE 14 :FIGURE 15 :
FIGURE 14: Point-of-care ultrasound sensitivity and specificity for deep vein thrombosis diagnosis.

TABLE 1 : Summary of study characteristics on the use of POCUS as a diagnostic tool in the emergency department.
On the other hand, five of the seven studies reporting the use of POCUS for procedure guidance were about peripheral venous access and the other two were about central venous access (Table2).