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Earlier point-of-care ultrasound, shorter length of stay in patients with acute flank pain

Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine volume 30, Article number: 29 (2022) Cite this article

Abstract

Background

The effects of early integration of point-of-care ultrasound (PoCUS) into patient care are uncertain. This study aims to investigate the effects of early PoCUS on patients with acute flank pain.

Methods

Adult non-traumatic patients with acute flank pain receiving PoCUS were enrolled. Expert physicians reviewed the medical records and made the “final diagnosis” for the cause of acute flank pain. The primary outcome was the relationship between the door to ultrasound (US) time and length of stay (LOS). The secondary outcomes included the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the sonographic diagnosis, compared with the final diagnosis.

Results

Eight hundred and eighty-eight patients were included in the analysis. Patients receiving early PoCUS (≤120 min) had a shorter LOS (128 vs. 217 min, p < 0.0001). Patients in the late POCUS group (> 120 min) had a trend to receive more CT scans. The disease distribution, sensitivity, specificity, PPV, and NPV were similar in patients receiving early or late PoCUS for target diagnoses. After adjusting for the confounders, early PoCUS (OR, 2.77, 95% CIs, 1.93–3.98) had a positive impact on shorter LOS. In addition, the effect of early PoCUS became more prominent (OR, 4.91, 95% CIs, 3.39–7.13) on LOS in less than 3 h.

Conclusions

Early integration of PoCUS is significantly related to shorter LOS in patients with acute flank pain without increasing morbidity and mortality. Our results suggested “PoCUS early” in these patients to possibly alleviate emergency department crowding.

Trial registration NCT04149041 at the ClinicalTrial.gov.

Background

Acute flank pain is a common symptom in the emergency department (ED). Acute ureteral obstruction from an impacted stone is the most frequent cause. However, a variety of diseases may manifest as acute flank pain, mimicking renal colic. Among them, pyelonephritis and myofascial pain are frequently encountered.

Besides a detailed medical history and physical examination, kidney-ureter-bladder (KUB) radiography and urinalysis are frequently used for the evaluation of acute flank pain although they exhibit a limited diagnostic value for urolithiasis [1, 2]. Currently, non-contrast computed tomography (CT) has become the gold standard for diagnosing acute flank pain, not only for urolithiasis but also for alternative diagnoses without the presence of the stone [3]. However, ionizing radiation and the costly expense of CT should be considered in emergency settings. A multicenter randomized trial demonstrated that initial point-of-care ultrasound (PoCUS) was associated with lower cumulative radiation exposure than initial CT. Notably, no significant differences in high-risk diagnoses, serious adverse events, and ED revisits between ultrasound (US) and CT [4]. However, the median length of stay (LOS) of patients remained more than 5 h in the PoCUS group, longer than the time targets (4 h) in emergency care [5].

With the advance of PoCUS, it can be used as an extension of the doctor’s hand to look inside and find out the possible etiology. The effects of early integration of PoCUS into actual patient care are uncertain. This study aims to investigate the effects of early PoCUS in the evaluation of ED patients with acute flank pain.

Methods

Study design and setting

The retrospective study was conducted at the ED of the National Taiwan University Hospital (NTUH), a tertiary medical center in Taiwan, between July 2015 and July 2017. The study protocol was approved by the Institutional Review Board of the Ethics Committee of the NTUH (201907173RIND) with a waiver of informed consent and registered at ClinicalTrials.gov (NCT04149041).

PoCUS was included in emergency residency US training since 2012, and all of the residents passed the hand-on assessment. The instructors were certified by the Taiwan Society of Ultrasound in Medicine and had more than 10 years of experience in sonographic examinations. All ultrasonographic examinations were written in a standard report form including indication, sonographic findings, sonographic diagnosis, and management.

Two US machines (SSA-550A, SSA-660, Canon, Japan) equipped with 2–5 MHz curvilinear transducers were set up and placed on standby for use.

Patient enrollment

Adult non-traumatic patients (more than 20-year-old) presenting with acute flank pain referred for PoCUS were eligible. Patients aged less than 20 years, with pregnancy or trauma were excluded.

Data collection

Clinical data were retrospectively obtained from the electronic medical records, including age, sex, body mass index (BMI), comorbidities, vital signs on arrival, time of visits, door to physician time, door to US time, door to KUB time, door to CT time, door to urinalysis time, ED LOS, and patient disposition, as well as the sonographic reports. The time of visits was categorized into weekday visits or weekend/holiday visits, as well as dayshift visits (8 a.m. to 8 p.m.) or nightshift visits (8 p.m. to 8 a.m.).

After patient discharge, expert ED physicians not involving PoCUS training reviewed the medical records and made the “final diagnosis” for the cause of acute flank pain (urolithiasis, pyelonephritis, myofascial pain, or others). The diagnostic criteria for urolithiasis included the presence of stones in the urinary tract in KUB, PoCUS, CT, or other imaging studies besides history and physical examination.

Outcome measurement

The primary outcome was the relationship between the door to US time and LOS. The secondary outcomes included the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the sonographic diagnosis, compared with the final diagnosis.

Statistical analysis

All data were analyzed by SAS software (SAS 9.4, Cary, North Carolina, USA). Categorical data were expressed in counts and proportions and compared using a Chi-square test, while continuous data were expressed in medians and interquartile ranges (IQRs), and examined using Wilcoxon’s rank-sum test.

The linear regression model was applied to investigate the relationship between the door to US time and LOS. Covariates in the model included age, sex, BMI, comorbidities, time of visits, and door to physician time. Further, the patients were divided into two groups by the door to US time ≤120 min (early) or > 120 min (late). Between-group differences for the parameters were investigated.

The logistic regression model was applied to investigate the early use of PoCUS (≤120 min) associated with shortened LOS (≤240 min) [5]. Covariates in the model were age, sex, BMI, comorbidities, time to visits, door to physician time, and door to US time categorized by 120 min. Odds ratios (ORs) were computed with 95% confidence intervals (CIs) for significant parameters. Also, the model was re-built using LOS of 180 min as the cut-point. A p-value of less than 0.05 was considered statistically significant.

Results

During the study period, 899 patients with acute flank pain received PoCUS. After excluding 11 patients without available documentation, 888 patients were included in the analysis (Table 1, Fig. 1). The median age was 51 years (IQR, 39–62 years), and 495 (56%) were men. The median door to physician time, door to US time, door to urinalysis time and ED LOS were 19 (IQR, 16–23), 35 (IQR, 20–82), 59 (IQR, 42–90), and 146 (IQR, 100–255) minutes, respectively. Eight hundred and five patients (91%) were discharged from the ED. No mortality was observed.

Table 1 The characteristics of the included patients
Full size table
Fig. 1
figure 1

The study flowchart

Full size image

We investigated the relationship between the door to US time and LOS using a linear regression model. The results showed that the shorter the door to US time, the shorter the LOS (coefficient, 1.30 ± 0.14, p < 0.0001) after adjusting for age, sex, BMI, comorbidities, time of visits, and door to physician time.

Moreover, we categorized the patients into 2 groups based on the door to US time in less than 120 min (early) or more than 120 min (late) (Table 1). Among the patients, 720 patients received early PoCUS and the median door to US time was 30 (IQR, 18–52) minutes. The remaining 168 patients received late PoCUS, and the median door to US time was 168 (IQR, 144–237) minutes. Patients receiving early PoCUS had a shorter LOS (128 vs. 217 min, p < 0.0001). There were no significant differences in age, sex, body max index, comorbidities, vital signs on arrival, time of visits, door to physician time, door to x-ray time, door to urinalysis time, CT rate, and ED discharge rate between the two groups (Table 1). Patients in the late POCUS group had a trend to receive more CT scans.

Moreover, the final diagnoses for the cause of acute flank pain included urolithiasis (57%), acute pyelonephritis (15%), myofascial pain (14%), and miscellaneous diagnoses. There was no significant association between the door to US time and final diagnoses (Table 2). The patterns of disease distribution were similar among the groups receiving early or late PoCUS.

Table 2 The distribution of the target conditions
Full size table

Furthermore, the logistic regression model was applied to investigate the factors associated with LOS less than 4 h. After adjusting for the confounders, early PoCUS (OR, 2.77, 95% CIs, 1.93–3.98) had a positive impact on shorter LOS. By contrast, patients with malignancy (OR, 0.54, 95% CIs, 0.30–0.98) had longer LOS. In addition, the effect of early PoCUS became more prominent (OR, 4.91, 95% CIs, 3.39–7.13) on LOS in less than 3 h.

The sensitivity, specificity, PPV, and NPV were similar in patients receiving early or late PoCUS for target diagnoses (Table 3). The presence of unilateral hydronephrosis on PoCUS was associated with high sensitivity, specificity, PPV, and NPV for the diagnosis of urolithiasis, whether in early or late PoCUS groups. However, normal kidneys (i.e. without the presence of hydronephrosis or other specific findings) in the sonographic finding had varying sensitivity and specificity for the diagnosis of pyelonephritis and myofascial pain.

Table 3 The sensitivity, specificity, positive predictive value, and negative predictive value of the sonographic findings for target diagnoses
Full size table

Discussion

Acute flank pain is a frequently encountered complaint at the ED. Compared with non-contrast CT, US has the advantage of bedside accessibility and a lack of ionic radiation. Our study investigated the effect of PoCUS on patient-centered outcomes. The results showed that the earlier use of PoCUS was associated with shorter ED LOS in patients with acute flank pain. An earlier PoCUS did not harm the diagnostic accuracy including sensitivity, specificity, PPV, and NPV.

Urolithiasis is the most frequent cause among patients with acute flank pain. Previous studies have suggested that US is the ideal initial imaging test in the ED setting for patients with suspected urolithiasis without changing patient outcomes and morbidity [4, 6]. Modern ED provided not only urgent care for life-threatening emergencies but also further diagnostic assessment and workups [7]. Thus, ED LOS was substantially increasing, which resulted in ED crowding and subsequent complications, and increased mortality [8, 9]. Moreover, a decrease in ED boarding and crowding would prevent in-hospital transmission and infection during the global COVID-19 pandemic. Our results well demonstrated that early integration of PoCUS in clinical practice was significantly associated with lessening ED LOS, possibly alleviating ED crowding. Also, the effect of early PoCUS remained significant after adjusting the door to physician time and other confounders, implying it was not associated with early or late access to the physician.

There have been still some concerns regarding the use of PoCUS for the diagnosis of urolithiasis. PoCUS has limited ability to visualize stones less than 3 mm [10], or in the mid-ureter due to the interference of overlying bowel gas. Also, a high BMI would result in unclear US images and restricted fields of view. On the other aspect, a small subset of patients with tiny ureteral stones does not develop hydronephrosis indeed. However, even in patients with severe hydronephrosis, permanent damage to the kidneys may only occur after 2 weeks; therefore, emergency interventions may not be required [11]. In this study, we adopted hydronephrosis as an indirect sign of urolithiasis, and the results presented with acceptable sensitivity and specificity. Also, the discharge rate was more than 90%, in agreement with a previous review [12]. Moreover, no adverse outcomes were observed.

In recent years, PoCUS has become a required milestone competency in residency practice [13,14,15,16]. PoCUS can be considered a “21st-century stethoscope” to evaluate a broad spectrum of illnesses and change the management of a wide variety of patients in emergent settings [17, 18]. A well-established training program with an easily accessible US machine is essential for effective incorporation into clinical care. However, previous studies mainly focused on the diagnostic accuracy of PoCUS compared with CT or US performed by radiologists [4, 10], rarely on how to integrate PoCUS during clinical practice. Our study provided evidence that PoCUS could be a part of the timely evaluation of acute flank pain.

Moreover, diseases of the abdominal aorta represent a category of life-threatening conditions, which present with flank pain [19]. In our study, 4 cases were diagnosed to have abdominal aortic aneurysms. Of them, 3 (75%) were diagnosed with early PoCUS, although there was no significant difference in diagnosing aortic aneurysms between early and late PoCUS. However, timely recognition and proper management would be beneficial to these patients to reduce morbidity and mortality [20].

There were limitations in this study. First, because our study was a retrospective design, some US images and records were missing. However, the missing data was only 1% and the results were representative of the large-scale study. Second, there were no absolute guidelines for how early to use US in patients with acute flank pain. It depended on physicians’ clinical discretions, which may result in selection bias. However, the distribution of etiologies was similar in patients receiving US in 120 min or later. Also, the diagnostic accuracy of PoCUS was similar between these two groups. Third, the factors influencing the LOS were multifactorial, occurring in the input, throughput, and output [21], although we had adjusted the selected covariates in the regression model. However, other factors which existed at the same time of patient visits such as already crowding, busy ED, or different doctors were hard to be explored due to a retrospective design. Fourth, we adopted a “normal” sonographic finding for the diagnosis of pyelonephritis or myofascial pain. Notably, a normal finding does not exclude the presence of other diseases, and the physician should correlate the sonographic finding into clinical context/supplemental tests. Last, our hospital was a teaching hospital where the comorbidity and disease patterns would be more severe and complicated. As the results shown in this study, a substantial percentage of patients presented with flank pain due to existing malignancies and exhibited a longer LOS. Also, someone would wonder if the longer LOS was a result of diagnostic uncertainty due to a less "typical" presentation. However, the disease patterns and the percentage of discharge were similar between the early and late PoCUS groups.

Conclusions

Early integration of PoCUS for ED patient care is significantly related to shorter LOS in patients with acute flank pain without increasing morbidity and mortality. Our results suggested “PoCUS early” in these patients to possibly alleviate ED crowding. However, many factors are involved in ED patient flow that further investigations should be explored.

Availability of data and materials

All data analyzed during this study are included in this published article.

Abbreviations

ED:

Emergency department

KUB:

Kidney-ureter-bladder

CT:

Computed tomography

PoCUS:

Point-of-care ultrasound

US:

Ultrasound

LOS:

Length of stay

NTUH:

National Taiwan University Hospital

BMI:

Body mass index

PPV:

Positive predictive value

NPV:

Negative predictive value

IQR:

Interquartile range

OR:

Odds ratio

CI:

Confidence interval

References

  1. Luchs JS, Katz D, Lane M, Mellinger BC, Lumerman JH, Stillman CA, et al. Utility of hematuria testing in patients with suspected renal colic: correlation with unenhanced helical CT results. Urology. 2002;59(6):839–42.

    Article  Google Scholar 

  2. Heidenreich A, Desgrandschamps F, Terrier F. Modern approach of diagnosis and management of acute flank pain: review of all imaging modalities. Eur Urol. 2002;41(4):351–62.

    Article  Google Scholar 

  3. Türk C, Petřík A, Sarica K, Seitz C, Skolarikos A, Straub M, et al. EAU guidelines on diagnosis and conservative management of urolithiasis. Eur Urol. 2016;69(3):468–74.

    Article  Google Scholar 

  4. Smith-Bindman R, Aubin C, Bailitz J, Bengiamin RN, Camargo CA Jr, Corbo J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med. 2014;371(12):1100–10.

    Article  CAS  Google Scholar 

  5. Reforming Emergency Care. In: Health, editor. UK; 2001.

  6. Wang RC, Rodriguez RM, Moghadassi M, Noble V, Bailitz J, Mallin M, et al. External validation of the STONE score, a clinical prediction rule for ureteral stone: an observational multi-institutional study. Ann Emerg Med. 2016;67(4):423-32.e2.

    Article  Google Scholar 

  7. Care E. Then, now and next. Health Affairs. 2013;32(12):2069–74.

    Article  Google Scholar 

  8. Chou CH, Chiu TF, Yen AM, Ng CJ, Chen HH. Analyzing FACTORS AFFECTIng Emergency Department Length of Stay-Using a Competing Risk-accelerated Failure Time Model. Medicine. 2016;95(14):e3263.

  9. Mowery NT, Dougherty SD, Hildreth AN, Holmes JHt, Chang MC, Martin RS, et al. Emergency department length of stay is an independent predictor of hospital mortality in trauma activation patients. J Trauma. 2011;70(6):1317–25.

  10. Fowler KAB, Locken JA, Duchesne JH, Williamson MR. US for detecting renal calculi with nonenhanced CT as a reference standard. Radiology. 2002;222(1):109–13.

    Article  Google Scholar 

  11. Manthey DE, Teichman J. Nephrolithiasis. Emerg Med Clin North Am. 2001;19(3):633–54.

    Article  CAS  Google Scholar 

  12. Dalziel PJ, Noble VE. Bedside ultrasound and the assessment of renal colic: a review. Emerg Med J. 2013;30(1):3–8.

    Article  Google Scholar 

  13. Hayward M, Chan T, Healey A. Dedicated time for deliberate practice: one emergency medicine program’s approach to point-of-care ultrasound (PoCUS) training. CJEM. 2015;17(5):558–61.

    Article  Google Scholar 

  14. Fischer LM, Woo MY, Lee AC, Wiss R, Socransky S, Frank JR. Emergency medicine point-of-care ultrasonography: a national needs assessment of competencies for general and expert practice. CJEM. 2015;17(1):74–88.

    Article  Google Scholar 

  15. PoSaw LL, Wubben BM, Bertucci N, Bell GA, Healy H, Lee S. Teaching emergency ultrasound to emergency medicine residents: a scoping review of structured training methods. J Am Coll Emerg Phys Open. 2021;2(3):e12439.

  16. Beal EW, Sigmond BR, Sage-Silski L, Lahey S, Nguyen V, Bahner DP. Point-of-care ultrasound in general surgery residency training: a proposal for milestones in graduate medical education ultrasound. J Ultrasound Med. 2017;36(12):2577–84.

    Article  Google Scholar 

  17. Feilchenfeld Z, Kuper A, Whitehead C. Stethoscope of the 21st century: dominant discourses of ultrasound in medical education. Med Educ. 2018;52(12):1271–87.

    Article  Google Scholar 

  18. Weile J, Frederiksen CA, Laursen CB, Graumann O, Sloth E, Kirkegaard H. Point-of-care ultrasound induced changes in management of unselected patients in the emergency department: a prospective single-blinded observational trial. Scand J Trauma Resuscitation Emerg Med. 2020;28(1):47.

    Article  Google Scholar 

  19. Lech C, Swaminathan A. Abdominal aortic emergencies. Emerg Med Clin North Am. 2017;35(4):847–67.

    Article  Google Scholar 

  20. Takagi H, Ando T, Umemoto T. Abdominal aortic aneurysm screening reduces all-cause mortality: make screening great again. Angiology. 2018;69(3):205–11.

    Article  Google Scholar 

  21. Asplin BR, Magid DJ, Rhodes KV, Solberg LI, Lurie N, Camargo CAJ. A conceptual model of emergency department crowding. Ann Emerg Med. 2003;42(2):173–80.

    Article  Google Scholar 

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Acknowledgements

We thank Wallace Editing for grammar editing.

Funding

Financial or grant support: the Ministry of Science and Technology, Taiwan (MOST 110-2511-H-002-009-MY2).

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Authors and Affiliations

  1. Department of Emergency Medicine, National Taiwan University Hospital, No. 7, Chung-Shan S. Road, Taipei, 100, Taiwan

    Pei-Hsiu Wang, Jia-Yu Chen, Dean-An Ling, An-Fu Lee, Ying-Chih Ko, Wan-Ching Lien & Chien-Hua Huang

  2. Department of Emergency Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan

    Wan-Ching Lien & Chien-Hua Huang

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  1. Pei-Hsiu Wang
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Contributions

PH and WC conceived the study and designed the trial. PH, JY, DA, AF, YC, and WC acquisition of the data. PH and WC analysis and interpretation of the data. PH and WC drafted the manuscript, and all authors contributed substantially to its revision. CH supervised the study. WC critically revised of the manuscript for important intellectual content and takes responsibility for the paper as a whole. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Wan-Ching Lien.

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Ethics approval and consent to participate

This study was approved by the Institutional Review Board of the Research Ethics Committee of the National Taiwan University Hospital (201907173RIND) with a waiver of informed consent.

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Not applicable.

Competing interests

The authors declare that they have no competing interests.

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Wang, PH., Chen, JY., Ling, DA. et al. Earlier point-of-care ultrasound, shorter length of stay in patients with acute flank pain. Scand J Trauma Resusc Emerg Med 30, 29 (2022). https://0-doi-org.brum.beds.ac.uk/10.1186/s13049-022-01017-1

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  • DOI: https://0-doi-org.brum.beds.ac.uk/10.1186/s13049-022-01017-1

Keywords

Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine

ISSN: 1757-7241