Radiology

Multi-center analysis of point-of-care ultrasound for small bowel obstruction: A systematic review and individual patient-level meta-analysis

a b s t r a c t

Objective: The study aimed to assess the diagnostic accuracy of Point-of-care ultrasound in identifying Small bowel obstruction (SBO) and to investigate the impact of clinician Experience level and body mass index (BMI) on POCUS performance for diagnosing SBO in the Emergency Department.

Methods: We systematically searched PubMed and Cochrane databases from January 2011-2022. We performed a meta-analysis using individual patient-level data from prospective diagnostic accuracy studies from which we obtained data from the corresponding authors. Overall test characteristics and subgroup analysis across clinician experience levels and a range of BMI were calculated. The primary outcome was SBO as the final diagnosis during hospitalization.

Results: We included Individual patient data from 433 patients from 5 prospective studies. Overall, 33% of patients had a final diagnosis of SBO. POCUS had 83.0% (95%CI 71.7%-90.4%) sensitivity and 93.0% (95%CI 55.3%-99.3%) specificity; LR+ was 11.9 (95%CI 1.2-114.9) and LR- was 0.2 (95%CI 0.1-0.3). Residents had exhibited a sensitiv- ity of 73.0% (95%CI 56.6%-84.9%) and specificity of 88.2% (95%CI 58.8%-97.5%), whereas attendings had demon- strated a sensitivity of 87.7% (95%CI 71.1%-95.4%) and specificity of 91.4% (95%CI 57.4%-98.8%). Among those patients with BMI<30 kg/m2, POCUS showed a sensitivity of 88.6% (95%CI 79.5%-94.7%) and a specificity of 84.0% (95%CI 75.3%-90.6%), while patients with BMI >= 30 kg/m2 exhibited a sensitivity of 72.0% (95%CI 50.6%- 87.9%) and specificity of 89.5% (95%CI 75.2%-97.1%).

Conclusions: POCUS correctly identified those patients with SBO with high sensitivity and specificity. Diagnostic accuracy was slightly reduced when performed by resident physicians and among patients with a BMI >= 30 kg/m2.

Registration: PROSPERO registration number: CRD42022303598.

(C) 2023

  1. Introduction

? Presentation: An abstract of the study was presented at the American College of Emergency Physicians 2021 Scientific Assembly, October 2021, Boston, MA.

* Corresponding author.

E-mail address: [email protected] (H. Shokoohi).

Small bowel obstruction (SBO) remains a common indication for Surgical consultation and potential surgical intervention in the Emergency Department (ED) [1]. management decisions for patients presenting with SBO mostly rely on radiographic imaging in the ED [2]. Therefore, identifying the optimal use of imagings in patients with

https://doi.org/10.1016/j.ajem.2023.05.039

0735-6757/(C) 2023

suspected SBO is essential. While computed tomography (CT) is widely used for diagnosing SBO due to its high sensitivity and specificity, it comes with drawbacks such as radiation exposure, increased costs, pro- longed diagnostic time, and extended ED length of stay. In searching for an alternative imaging modality with high accuracy and real-time per- formance, Point-of-care ultrasound has emerged as an initial, and potentially cost-saving imaging modality for patients with suspected SBO in ED [3].

As the use of POCUS for SBO increases, it is essential to understand how this modality performs across different subgroups of patients and clinicians. Multiple studies have investigated the diagnostic value of POCUS in patients with SBO [3-6]. In most instances, these studies evaluated imaging performed by radiologists or performed on patients outside of the ED [7-10]. In 2011, the first studies on the use of POCUS in SBO were published by Emergency Physicians (EPs) on ED patients [11,12]. Since then, several other ED-based POCUS studies to evaluate SBO have contributed to our understand- ing of this application [13,14]. However, these studies have reported variable diagnostic performance, and ultrasound’s accuracy in the early detection of SBO remains a subject of debate [4]. For example, the accuracy of ultrasound for diagnosing SBO has varying reported sensitivity ranging from 70% to 100%, and the specificity ranging from 80% to 100% [5-7]. In addition, it is unclear in which patient subgroups POCUS performs best, as many of the prior studies were limited by variations in sonographers and patient characteristics. Therefore, there is a need to better understand POCUS accuracy by analyzing patient-level data within specific groups.

To further delineate the accuracy of POCUS for the diagnosis of SBO, we performed a meta-analysis utilizing individual patient-level partici- pant data obtained from prospective studies examining POCUS for SBO in the ED.

  1. Methods
    1. Study design

This study conformed to the Preferred Reporting Items for System- atic Reviews and Meta-Analyses – Diagnostic test accuracy (PRISMA- DTA) guidelines for systematic reviews. It was performed in accordance with best practice guidelines [15]. This review was registered with PROSPERO (blinded for peer review). In conjunction with a medical librarian, we searched PubMed, the Cochrane Database of Systematic Reviews, and the Cochrane Central Register of Controlled Trials to include citations over eleven years from January 2011-2022. The following text words and corresponding heading terms were used as search terms: “Point-of-care ultrasound,” “POCUS,” “Ultrasonography,” “Ultrasound”, “US”, “bowel obstruction”, “SBO”, “small bowel obstruc- tion”, “intestinal obstruction” and “small intestinal obstruction We also reviewed the bibliographies of all included studies and review arti- cles for potential missed articles. We also consulted with topic experts to help identify further relevant studies. According to our institutional IRB protocols, the study was exempt as it did not involve human sub- jects, and the data were previously de-identified and were publicly available information from the data sets.

    1. Selection of studies

We included all prospective observational or randomized control tri- als performed within the study period that assessed POCUS to identify SBO. We limited our search to the most recent studies to ensure access to the original individual patient-level data and consistent technology, given advances in Ultrasound imaging technology.

Studies were included if: (1) they were prospective studies of adult patients evaluated in the ED for suspected SBO; (2) EPs per- formed POCUS studies; (3) the studies had CT scans or operative data to determine the diagnosis of SBO, (4) they had an adjudicated

endpoint of a confirmed or excluded SBO in ED visits or during their hospitalization, and (5) the authors could provide access to the orig- inal clinical and sonographic data needed for analysis. Studies were limited to those conducted in the English language and involving adult patients. We excluded case reports, retrospective studies, and review articles.

The corresponding authors of each eligible study were contacted, and anonymized original raw data encompassing demographic charac- teristics, clinical findings, detailed sonographic features, and diagnoses, as well as data on the final adjudicated diagnoses, were obtained. All data were prospectively collected, and studies were conducted with ap- proval from their institutional review board. Two investigators inde- pendently assessed studies for eligibility. All titles and abstracts meeting the initial criteria were reviewed as full manuscripts. Studies determined to meet the eligibility criteria on full-text review by both extractors were included in the final data analysis. Any discrepancies were resolved by consensus with the addition of a third reviewer if needed.

    1. Data collection and processing

Two investigators independently extracted data from the included studies. The investigators underwent initial training and extracted data into a pre-designed, piloted data collection form. The following in- formation was abstracted: last name of the first author, Publication year, study country, study population size, type of study (e.g., prospective or randomized controlled trial), study location (e.g., ED, Intensive Care Unit), study inclusion criteria, study exclusion criteria, the mean age of study patients, gender of study patients, sex, body mass index (BMI), presence of SBO (as defined in the original study), level of training (at- tending/fellow physician or resident physician), CT diagnosis, discharge diagnosis, true positives, false positives, true negatives, and false nega- tives for both ultrasound and CT for identifying SBO. The discharge diag- nosis of SBO was collected to capture the comprehensive assessment of SBO during the patient’s hospital stay and incorporate additional infor- mation, such as surgical operation reports. Studies were independently assessed for quality by two separate investigators utilizing the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool [16]. Any discrepancies were resolved by consensus with the addition of a third reviewer if needed.

    1. Analysis

Individual patient-level data were obtained for all studies. Data from included studies with more than one study institution were separated by the site due to innate variables that study protocols may not control. True positives, true negatives, false positives, and false negatives were entered into 2 x 2 tables and analyzed using a bivariate mixed-effects regression model. Exact binomial calcula- tions were used for instances of low study inclusion. Diagnostic accu- racy summary estimates included sensitivities, specificities, positive likelihood ratios (LR+), and negative likelihood ratios (LR-) with 95% confidence intervals (95% CIs). Summary estimates were incor- porated into figures, including forest plots and a summary receiver operating characteristic (SROC) curve.

Exploration of heterogeneity was completed both visually and statistically. Visual inspection included a review of forest plots and the SROC curve. Statistical heterogeneity was assessed as significant when either a Chi-square test yielded a p-value less than 0.1 or an I2 statistic that was greater than 50%. A priori, it was determined to evaluate for differences by the expertise of the individual performing POCUS (resident versus fellow/attending) and BMI (<30 kg/m2 versus >=30 kg/m2).

Bivariate mixed-effects regression was completed with the MIDAS module for StataMP, version 13 (StataCorp LP, College Station, Texas). The exact binomial method was conducted using the DIAGT module.

Forest plots were constructed using RevMan (The Nordic Cochrane Centre, Copenhagen, Denmark), version 5.3.

  1. Results
    1. Study selection and inclusion process

The initial search identified 486 total studies. PubMed identified 415 studies, Scopus identified 62 studies, and the Cochrane Central Register of Controlled Trials (CENTRAL) identified 5 studies. We identified 2 additional studies in a manual bibliography search. After removing duplicates, case reports, and review articles, we identified 22 eligible studies for which we conducted full-text reviews.

A total of 5 studies were included in the final analysis after excluding

17 studies for retrospective design (10), performance by non- emergency providers (6,) or the authors’ inability to access the original individual data (1). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram is contained in Fig. 1. (Fig. 1).

    1. Characteristics of the included studies and patient population

The 5 eligible studies included in the meta-analysis consisted of pub- lished studies, for which we sought individual patient data by contacting authors. In one study by Jang et al. [12], we could only retrieve data for a limited sample of the original study due to a lack of access to the original hardware.

For the individual patient-level meta-analysis, we analyzed data from a total of 433 subjects (Table 1). All 5 studies were conducted in the United States and were performed in the ED setting. The mean age was 55 years, and 54.7% of the patients were female. Detailed informa- tion on patients presenting symptoms, US findings, and the need for surgical interventions are listed in Supplemental Table 1. The preva- lence of SBO was 33.0%. Three studies used a curviLinear probe [13,17], one study used a phased array probe [12], and one study used both a phased array and linear probe [14]. (Table 1).

Studies had a low risk of bias and applicability concerns for most components (Table 2 – QUADAS Table). All included studies were at un- clear risk of bias for patient selection due to a convenience sample. Fur- thermore, all included studies had applicability concerns for the index test evaluated as unclear because of the potential for changes in ultra- sound machine/Image quality over time and the potential use of multi- ple types of ultrasound transducers. No studies were at high risk for bias or applicability.

    1. Overall diagnostic performance of POCUS for SBO

Overall, POCUS had 83.0% (95% CI 71.7% to 90.4%) sensitivity and

93.0% (95% CI 55.3% to 99.3%) specificity for the diagnosis of SBO with

an LR+ of 11.9 (95% CI 1.2 to 114.9) and an LR- of 0.2 (95% CI 0.1 to

0.3) (Fig. 2). The summary receiver operating characteristic (SROC) curve indicated high accuracy with a value of 88.9% (95% CI 85.9% to 91.4%) (Fig. 3). Statistical heterogeneity was significant, with an I2 of 73%, which was confirmed by visual inspection.

    1. Subgroup analysis by clinician experience level

In the assessment of clinician experience level, residents (n = 131) performing POCUS for SBO exhibited a sensitivity of 73.0% (95% CI 56.6% to 84.9%) and a specificity of 88.2% (95% CI 58.8% to 97.5%) with

an LR+ of 6.2 (95% CI 1.4 to 27.6) and an LR- of 0.3 (95% CI 0.2 to 0.5)

(Supplemental Fig. 1). Fellow and attending clinicians (n = 302) had a sensitivity of 87.7% (95% CI 71.1% to 95.4%) and specificity of 91.4%

(95% CI 57.4% to 98.8%) with LR+ of 10.2 (95% CI 1.4 to 71.8) and LR-

of 0.1 (95% CI 0.05 to 0.4) (Supplemental Fig. 2). The area under the SROC curve for residents was 75.4% (95% CI 71.5% to 79.0%), and for fel- lows and attendings, it was 94.0% (95% CI 91.6% to 95.8%) (Figs. 4 and 5).

    1. Subgroup analysis by body mass index (BMI)

Two studies, encompassing 3 study sites, recorded BMI data. Among patients with BMI < 30 kg/m2 (n = 179), POCUS had a sensitivity of

Image of Fig. 1

Fig. 1. Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) individual patient data flow diagram.

Table 1

Demographic data for studies included in meta-analysis?.

First Author

Year

Study Title

Study Dates

Total Study Population Size

Mean Patient Age

Total Number (%) Female Patients

Total SBO (%)

Ultrasound Probe

and Machine

Sonographers

Training Protocol

Ultrasound Criteria for SBO

Jang

2011

Bedside

2006-2007

44

51 years

23 (52.3%)

17

Phased Array

Resident

10-min

1) Presence of

ultra-sonography

for the detection of

(38.6%)

(Ultrasonix

CEP)

physicians

hands-on

lecture and

fluid-filled, dilated bowel (>= 25 mm)

small bowel

performance of

proximal to normal

obstruction in the

5 prior

or collapsed bowel or

emergency

ultrasound SBO

2) decreased or

department

exams

absent bowel

peristalsis

Becker

2019

A Prospective,

2014-2017

214

56 years

113 (52.8%)

88

Curvilinear

Resident,

30-min lecture

Primary Criteria:

Multicenter

(41.1%)

Probe

Fellow, or

and brief

1) Small bowel

Evaluation of

(Mindray TE7,

Attending

hands-on

dilation >=25 mm

Point-of-care

SonoSite

physicians

scanning

2) Abnormal

Ultrasound for

M-Turbo,

practice on

peristalsis

Small-bowel

SonoSite

normal

Supplemental

Obstruction in the

X-porte,

individuals

Criteria:

Emergency

Ultrasonix

without SBO

1) Intraperitoneal

Department

SonixTOUCH,

free fluid

Zonare ZS3)

2) Small-bowel wall

edema

3) Transition point

Boniface

2019

Diagnostic Accuracy

NR

140

54 years

79 (56.4%)

21

Phased Array

Resident,

20-min lecture

1) Small bowel

and Time-Saving

(15%)

and Linear

Fellow, or

and hands-on

diameter >= 25 mm

Effects of

Probe

Attending

scanning

and

Point-of-Care

(SonoSite

physicians

practice on 5

2) Abnormal

Ultra-sonography

Edge, SonoSite

precepted scans

peristalsis

in Patients With

Xporte, Zonare

on patients

Small Bowel

Z1 Ultra)

without SBO

Obstruction: A

Prospective Study

Singer

2022

Can point-of-care

2019-2020

35

59 years

22 (62.9%)

17

Curvilinear

Resident,

15-min lecture

1) Small bowel

ultrasound speed

(48.6%)

Probe

Fellow, or

and hands-on

diameter >= 25 mm

up time to

(Mindray M9,

Attending

scanning

and

diagnosis for small

Mindray TE7,

physicians

practice on 5

2) Abnormal

bowel obstruction?

SonoSite Edge

precepted scans

peristalsis

II)

on patients with

suspected SBO

NR = not reported.

* All studies were conducted in the United States and were performed in the ED setting.

88.6% (95% CI 79.5% to 94.7%) and a specificity of 84.0% (95% CI 75.3% to 90.6%) with an LR+ of 5.5 (95% CI 3.5 to 8.7) and LR- of 0.1 (95% CI 0.1 to

0.3) (Supplemental Fig. 3). In patients with BMI >= 30 kg/m2 (n = 63), POCUS exhibited a sensitivity of 72.0% (95% CI 50.6% to 87.9%) and a specificity of 89.5% (95% CI 75.2% to 97.1%) with an LR+ of 6.8 (95% CI 2.6 to 17.8) and LR- of 0.3 (95% CI 0.2 to 0.6) (Supplemental Fig. 4). The area under the SROC curve for BMI < 30 kg/m2 versus BMI >= 30 kg/m2 were similar, with values of 86.3% (95% CI 81.3% to 91.4%) and 80.7% (95% CI 70.5% to 91.0%), respectively.

  1. Discussion

In the meta-analysis of individual patient-level data from 5 pro- spective studies, we found that POCUS performed by EPs had consid- erable diagnostic accuracy with an overall high sensitivity of 83.0% and a specificity of 93.0% for the diagnosis of SBO. These findings

highlight the potential of POCUS as a valuable tool in the ED for accu- rately identifying SBO cases, thereby aiding in timely management decisions. The test characteristics were consistent across all test sites and individual cohorts, suggesting enhanced generalizability of the findings.

The analysis also revealed variations in diagnostic performance

based on clinician experience level, with higher sensitivity and specific- ity observed among fellow and attending clinicians compared to resi- dents. This contradicts some prior literature showing that residents perform at the same level as attending radiologists in diagnosing ab- dominal pathology by ultrasound [18]. Differentiating between clini- cians with ultrasound Fellowship training and those without was not possible in our study due to the lack of specific data available in the in- cluded studies. Therefore, we were unable to directly analyze and com- pare the test characteristics between these two groups in our current study. However, compared to studies performed by radiologists, our

Table 2

Quality assessment of diagnostic accuracy studies (QUADAS-2) for included studies.

Study

Risk of Bias

Applicability Concerns

Patient Selection

Index Test

Reference Standard

Flow and Timing

Patient Selection

Index Test

Reference Standard

Jang 2011

U

L

L

L

L

U

L

Becker 2019

U

L

L

L

L

U

L

Boniface 2020

U

L

L

L

L

U

L

Singer 2022

U

L

L

L

L

U

L

L, Low risk of bias; U, Unclear risk of bias.

Image of Fig. 2

Fig. 2. Forest diagram of POCUS for SBO accuracy.

study revealed a lower sensitivity (83% vs. 92%) and specificity (93% vs. 97%) [3]. These differences in performance may be attributed to varia- tions in training, ultrasound machines, patient populations, or tech- niques utilized.

Furthermore, the analysis of patient subgroups based on BMI showed slightly lower sensitivity in patients with BMI >= 30 mg/kg2 compared to those with a BMI < 30 mg/kg2. This may be because a larger body habitus makes the test technically more challenging, and caution should be emphasized when using this examination among those with a higher BMI. However, it is worth noting that this finding contrasts with some previous studies in the literature, particularly in pe- diatric populations, which have shown that BMI does not significantly impact POCUS sensitivity for conditions like appendicitis [19]. The re- sults underscore the importance of clinician expertise and patient char- acteristics in influencing POCUS accuracy.

To our knowledge, this is the first patient-level meta-analysis assessing the diagnostic accuracy of POCUS for SBO, incorporating data from all available studies conducted in ED patients with a larger aggre- gate sample size, allowing meaningful analysis of important subgroups. While a prior systematic review and meta-analysis comparing ultra- sound accuracy in SBO existed, it did not exclusively include prospective studies or individual patient-level data [20]. Therefore, our findings have significant implications for optimizing POCUS utilization in differ- ent patient populations and by various clinicians, potentially aiding physicians in identifying suitable candidates for POCUS. Nevertheless, the question of whether POCUS can replace CT scans or enhance Clinical effectiveness in suspected SBO patients warrants further investigation.

In our study, the discharge diagnosis of SBO was considered as the confirmatory test, as it reflects the final diagnosis made during the patient’s hospitalization, incorporating additional diagnostic tests, and surgical findings beyond the initial ED assessment. While we ac- knowledge the importance of CT as a diagnostic tool, we wanted to capture the comprehensive assessment of SBO throughout the patient’s hospital stay. Although there is a possibility of discordance between the discharge diagnosis and other diagnostic tests, in most cases, the CT diagnosis and the discharge diagnosis of SBO would be congruent, as clinicians rely on all available information for the final diagnosis.

The findings of this study should be cautiously interpreted as they

may not be applicable in all settings and could be influenced by re- source limitations in certain settings. These studies were done under the supervision of EM physicians with specialized expertise in ultrasound. Further research is needed to determine the generaliz- ability of these findings to individuals without the same level of ex- pertise. Moreover, the wide confidence intervals for sensitivity and specificity suggest potential variability in accuracy across different sites and providers. Regardless of the setting, continuous quality as- surance and training programs are vital for clinicians to ensure the appropriate and effective use of ultrasound. This underscores the im- portance of POCUS stewardship and upholding the principles of re- sponsible and judicious utilization of ultrasound in clinical practice [21,22,23].

This study has a few limitations to consider. First, one study was ex- cluded due to unavailable individual patient-level data, which could

Image of Fig. 3 Image of Fig. 4

Fig. 3. Summary receiver operating characteristic curve of POCUS for SBO.

Fig. 4. Summary receiver operating characteristic curve of POCUS for SBO – subgroup cli- nician-level residents.

Image of Fig. 5

Fig. 5. Summary receiver operating characteristic curve of POCUS for SBO – subgroup cli- nician-level fellows and attendings.

introduce bias. Second, the included studies were conducted in specific settings, predominantly in the United States, which may limit the gener- alizability of the findings to other healthcare systems or regions with different resource availability. Third, heterogeneity was observed among the included studies, potentially influenced by variations in study design, patient populations, and technical factors. This heteroge- neity may impact the overall estimates of sensitivity and specificity; however, we addressed this by conducting an individual patient-level meta-analysis. Fourth, while we made extensive efforts to identify rele- vant studies, there is still a possibility of missing some. Finally, the find- ings of this study are specific to adult patients and may not be generalizable to the pediatric population.

In conclusion, this meta-analysis provides encouraging evidence supporting the use of POCUS by EPs in evaluating SBO. POCUS demon- strates high sensitivity and specificity in diagnosing SBO, making it a valuable tool in the ED. Future research should focus on optimizing the implementation of POCUS in clinical practice, including its predic- tive ability for surgical intervention, and identifying specific patient sub- groups that benefit most from its use. Continued quality assurance and training programs are essential to ensure the appropriate and effective use of POCUS in the management of SBO.

Supplementary data to this article can be found online at https://doi. org/10.1016/j.ajem.2023.05.039.

Source of support

This research received no specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CRediT authorship contribution statement

Hamid Shokoohi: Data curation, Conceptualization, Methodology, Writing – original draft, Writing – review & editing. Katherine Dickerson Mayes: Writing – review & editing, Writing – original draft, Formal analysis, Data curation. Gary D. Peksa: Writing – review & editing, Formal analysis. Michael A. Loesche: Writing – review & editing, Formal analysis. Brent A. Becker: Writing – review & editing, Resources. Keith S. Boniface: Writing – review & editing, Resources,

Conceptualization. Shadi Lahham: Writing – review & editing, Resources. Timothy B. Jang: Writing – review & editing, Resources. Mi- chael Secko: Writing – review & editing, Resources. Michael Gottlieb: Writing – review & editing, Writing – original draft, Conceptualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influ- ence the work reported in this paper.

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