Injury
Volume 38, Issue 1 , Pages 71-75, January 2007

The accuracy of focused assessment with sonography in trauma (FAST) in blunt trauma patients: Experience of an Australian major trauma service

  • Jeremy M. Hsu

      Affiliations

    • Department of Surgery, Royal North Shore Hospital, St. Leonards, NSW, Australia
    • ,
  • Anthony P. Joseph

      Affiliations

    • Emergency Department and Trauma Service, Royal North Shore Hospital, St. Leonards 2065, NSW, Australia
    • Corresponding Author InformationCorresponding author. Tel.: +61 299267921; fax: +61 299068123.
    • ,
  • Lisa J. Tarlinton

      Affiliations

    • Department of Surgery, Royal North Shore Hospital, St. Leonards, NSW, Australia
    • ,
  • Lewis Macken

      Affiliations

    • Department of Emergency Medicine, Royal North Shore Hospital, St. Leonards, NSW, Australia
    • ,
  • Steven Blome

      Affiliations

    • Department of Radiology, Royal North Shore Hospital, St. Leonards, NSW, Australia

Accepted 6 March 2006.

Article Outline

Summary 

Focused assessment with sonography for trauma (FAST) is a method for detecting haemoperitonem in trauma patients on initial assessment in the Emergency Department. The aim of this paper is to present an Australian trauma centre's experience with FAST as a tool to screen for intraabdominal free fluid in patient's sustaining blunt truncal trauma.

Method

Over a 63-month period, FAST scans were prospectively studied and compared with findings from a gold-standard investigation, either computed tomography (CT) or laparotomy.

Results

463 FAST results were collected prospectively from 463 patients. 53 scans were excluded due to lack of a corresponding confirmatory gold-standard test. Overall sensitivity, specificity, positive and negative predictive values for FAST in detecting free fluid were 78%, 97%, 91%, 93%, respectively. Analysis of the credentialed operators demonstrated an improvement in accuracy (sensitivity 80%, specificity 100%, positive predictive value 100%, negative predictive value 94%). These findings are comparable with documented international experience.

Conclusion

The study demonstrates that the use of non-radiologist performed FAST in the detection of free fluid is safe and accurate within an Australian Trauma Centre.

Keywords: Ultrasound, FAST, Trauma, Emergency, Free fluid, Haemoperitoneum

 

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Introduction 

Focused assessment with sonography for trauma (FAST) has been used, world-wide, for the detection of haemoperitoneum/free fluid in the trauma patient's initial workup. The accuracy of FAST performed by non-radiologists has been well documented in the published literature.

Although these focused examinations are becoming an accepted practice in many trauma centres, the published experience utilising FAST within Australasia is limited.35, 18

This report examines an Australasian institution's experience with FAST performed by non-radiologists in the Emergency Department.

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Method 

The study site is a 600 bed tertiary referral teaching hospital, which is designated as the Major Trauma Service for a population of approximately 800,000 people.

Between September 1999 and December 2004, FAST were prospectively analysed for the evaluation of patients with potential truncal injuries. Any trauma patient who came through the emergency department underwent a FAST study if the appropriate personnel were available. Those patients, who did not have the ultrasound results confirmed by either computed tomographic scanning (CT-scan) or laparotomy, were excluded from the study.

Information was collected on a pre-determined data sheet.

Haemodynamic instability was defined as a systolic blood pressure<90mmHg and/or a persistent tachycardia>120 beats per minute, unresponsive to fluid administration as per ATLS guidelines.

The study was approved by the hospital's Research and Ethics Committee.

Personnel and training 

All ultrasound scans were performed in the Emergency Department by Emergency Medicine Consultants, Emergency Medicine Registrars or Surgical Registrars. A total of 17 sonographers (seven emergency consultants, eight emergency registrars and two surgical registrars) performed the FAST examinations during the study period. All physicians completed an ultrasound training course, which included a minimum 8h of didactic teaching, videotapes, and practical sessions. Two emergency consultants were already fully credentialed as per the Australasian Trauma Society (ATS)/Australasian College of Emergency Medicine (ACEM) standards.

Technique 

The ultrasound examinations were performed with a B-K Medical Panther (Scan Medics, Chatswood NSW Australia, distributor for B-K Medical, Herlev Denmark) ultrasound system located within the resuscitation area. It was equipped with a 3.5–5.0MHz curvilinear transducer, a printer and a video recorder.

For FAST, the standard four areas were examined for the presence of free intraperitoneal fluid, namely, Morrison's pouch, the splenorenal recess, the pelvis and the pericardial area.28, 29 No attempt was made to delineate solid organ injury. The ultrasonographic appearances for free fluid have been well described in the literature.

Confirmatory studies 

All included studies were compared with the radiologist's formal CT scan report, or the surgeon's operative notes. At the study institution, there was no quantitative measurement of free fluid seen on CT scans.

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Results 

A total of 463 FAST examinations were carried out on 463 patients. All of the patients sustained blunt truncal trauma. About 53 scans were excluded due to lack of a corresponding gold-standard investigation. Average age was 37.1±23 years old. Only five patients were under the age of 16. 71% were males and 29% females. The results of the FAST examinations are shown in Table 1.

Table 1. Results of FAST examinations
True positive78
False negative22
True negative302
False positive8
Total scans410
Sensitivity78% (95% CI: 70–86)
Specificity97% (95% CI: 96–99)
Positive predictive value91% (95%CI: 85–94)
Negative predictive value93% (95%CI: 90–96)
Accuracy93% (95% CI: 90–96)
Error7% (95% CI: 4–10)

Further analysis was carried out on those scans performed by the two credentialed physicians, as shown in Table 2.

Table 2. Results of FAST examinations by credentialed physicians (n=2)
True positive33
False negative8
True negative116
False positive0
Total scans157
Sensitivity80% (95% CI: 73–88)
Specificity100%
Positive predictive value100%
Negative predictive value94% (95% CI: 91–96)
Accuracy95% (95% CI: 93–97)
Error5% (95% CI: 3–7)

All of the false negative examinations were confirmed by CT scan. Trace free fluid, predominantly in the pelvis, was the main finding on CT scans of those patients with false negative FAST examinations. Three patients with negative FAST examinations were found to have a low grade splenic laceration with free fluid, but none required a laparotomy.

30 patients had their positive ultrasound findings confirmed by laparotomy. Of these 30, 18 patients were haemodynamically unstable and taken directly from the resuscitation room to the operating theatre. The mechanism and operative findings on these unstable patients are shown in Table 3.

Table 3. Operative findings of haemodynamically unstable patients with a positive FAST
AgeSexMechanismOperative findings
29MaleMVCGrade II splenic injury
46MaleBoatingGrade IV splenic injury
24MaleExplosionGrade V splenic injury
30MalePedestrianGrade IV splenic injury
41FemaleMVCGrade IV splenic injury
49MaleMBCGrade IV splenic injury
25MaleMBCGrade IV splenic injury
22MaleMVCSmall bowel and sigmoid mesenteric tear
28MaleMVCGrade III liver injury, pancreatic contusion
62MaleCrushRight hepatic artery transection, common bile duct transection
23MaleMVCGrade IV splenic injury
39MaleMVCDiaphragm laceration
28MaleMBCGrade III liver injury, ruptured duodenum, pancreas laceration
84FemaleMVCGrade III splenic injury, ruptured diaphragm, ruptured left ventricle
29MaleMVCGrade III liver injury, small bowel perforation
30MaleMVCGrade IV splenic injury
23MaleMBCSmall bowel mesenteric tear
49MaleFallSmall bowel mesenteric tear

MVC, motor vehicle crash and MBC, motorbike crash.

No laparotomies were performed for the false positive examinations.

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Discussion 

This study represents the largest series to date of ultrasound examinations performed by non-radiologists for trauma in Australasia.

When compared to those studies which examine non-radiologist performed ultrasounds, the sensitivity and specificity in our series (sens 78%, spec 97%) compares favourably (sens 69–98%, spec 85–99%).35, 26, 27, 28, 29, 15, 16, 17, 18, 19, 34, 21, 12, 8, 9, 32, 23

The values are also comparable to those studies which utilise sonographer/radiology resident/radiologist performed/interpreted scans (sens 69–93%, spec 98–100%).7, 22, 14, 11, 25

It is very important to note that definitions vary somewhat in the existing literature. All papers define a positive ultrasound result, be it true or false, and a false negative result, by means of a confirmatory gold-standard investigation, namely CT, Diagnostic Peritoneal Lavage (DPL) or laparotomy. However, the vast majority of studies define those patients with a negative FAST and a benign course of clinical observation, as a true negative examination. Some studies do not specify exactly how many true negative examinations were determined by clinical observation, while those which do, have between 34% and 96% of their total true negative examinations confirmed by clinical observation. This has been identified as a weakness by many authors, given the lack of long-term follow-up.

We chose only to include those examinations which had a corresponding gold-standard investigation, as we believe this to be a more accurate assessment of FAST. An international consensus conference on FAST also agreed that in the pure statistical sense, all true negatives should be confirmed by a standard test, however it may be impractical to confirm all negative results with an additional study.30 One can only speculate as to how many patients with a negative FAST and negative clinical observation period would have had intraperitoneal free fluid if a gold-standard confirmatory test been carried out. Thus, these studies involving clinical observation may be not be a strictly accurate assessment of FAST, in the true methodological sense. When looking at studies which include only those examinations with a confirmatory gold-standard investigation, the range of sensitivities and specificities are much narrower (sens 70–81%, spec 97–98%).35, 18, 8, 9

The false negative examinations in our series were largely clinically insignificant, as all but three examinations demonstrated only a trace of free fluid in the pelvis on CT scanning, with no subsequent laparotomy required. In this study, the subdiaphragmatic space above the spleen was not imaged on a regular basis, and thus was probably a significant contributory factor in the false negative examinations with splenic injuries. Also, there is the possibility that fluid may have accumulated during the time between the initial ultrasound examination and the subsequent CT scan. There does appear to be a minimal amount of free fluid required for ultrasound detection, however, the quantitative amount has not been accurately described in the literature. Two North American studies have used a model infusing fluid into trauma patients via a DPL catheter. The mean amount of fluid able to be detected was 619 and 668ml.10, 1

These studies have limitations as they only examined a single area of the abdomen, namely Morrison's pouch. Lentz and McKenney have made two comments relevant to these studies. Firstly, the models reflect the amount of instilled fluid required to overflow from the pelvis into Morrison's pouch, not the minimal detectable amount of fluid. Secondly, during a trauma ultrasound examination, multiple areas must be scanned, since the flow of intraperitoneal fluid is determined by peritoneal anatomic compartmentalisation, and that various factors will influence where fluid may accumulate including gravity, changes in intra-abdominal pressure and the injured organ of origin.20

In the Branney study, the minimal volume detectable was 225ml.10 Further support for a minimal ultrasound detectable amount of fluid is evidenced in a series by Miller et al., where 20 out of 22 false negative FAST studies had ≤300ml of fluid seen on CT scanning.24

With the knowledge that small amounts of free fluid may be undetectable by ultrasound, it has been recommended that, at a minimum, a negative FAST result in a haemodynamically stable patient be followed by a period of observation and at least one follow-up FAST examination.30 Currently there is minimal quantitative evidence to support the use of repeat FAST examinations.6 However, this is an area which requires further investigation.

It has been suggested that standard credentialing criteria should be set forth by a nationally recognised organisation.30 Within Australasia, the Australasian College of Emergency Medicine (ACEM) and the Australasian Trauma Society (ATS) have published credentialing policies. Both specify that an ultrasound workshop is essential, however only the ATS guidelines specify a minimum of 16 workshop hours. Both organisations require a minimum of 25 proctored scans with at least five positive scans.4, 5

Recommendations from other countries are more variable. In Germany, ultrasound use is incorporated into surgical residency training. The requirements are 15h in theory and 15h in practice, with a minimum of 400 examinations under supervision.15 In the USA, most published guidelines by national organisations, such as the Society for Academic Emergency Medicine and the American Institute of Ultrasound in Medicine refer to broader ultrasound examinations and are therefore not applicable to FAST credentialing alone.2, 3 Otherwise, training and credentialing appears to be institute specific.

Several studies have attempted to elucidate the learning curve involved with FAST examinations. Thomas et al. demonstrated that the accuracy of ultrasound examinations plateaued after an average of 50 examinations per trauma fellow.33 Their results were consistent with the published literature (sens 81%, spec 99%), after a single 8h trauma ultrasound course and a minimum of 50 proctored examinations. Gracias et al. hypothesised that more experienced providers would perform FAST with greater accuracy, by utilising peritoneal dialysis patients as models for injured patients with free fluid. They concluded that the learning curve for FAST starts to flatten out at 30–100 examinations.13

The prevalence of free fluid in our series was 24% with a pooled error rate of 7%. This is consistent with the arbitrary error rate of 8% suggested by Shackford et al.31 Their conclusion for reasonable credentialing criteria was a didactic course of 4h and a minimum of 30 examinations to determine the error rate. Jones et al. similarly described a pooled error rate of 10% (prevalence 22%) in their series assessing the ACEM/ATS credentialing criteria.18 When looking at the results from the two prior credentialed physicians in our series, the ACEM/ATS criteria appear to be acceptable to ensure accurate credentialing.

Limitations 

This study was based on a convenience sample, and as such may have some bias. No comment could be made on an accurate time required for FAST, as the time data sheet was often incomplete.

Our findings are not applicable in children or penetrating trauma, as there were no cases of penetrating trauma, and only 5 patients under 16 included in the study.

Conclusion and future directions 

This study has demonstrated that the use of ultrasound in assessing blunt trauma patients by non-radiologists within an Australian trauma centre, is safe and accurate.

Further studies are needed to determine cost-benefit within Australasia. In addition, the role of repeat ultrasound examinations needs to be further investigated.

National training bodies, such as the Australasian College for Emergency Medicine and the Royal Australasian College of Surgeons, need to consider the implementation of FAST into the trainee curriculum. Hospitals utilising a FAST service must introduce clear credentialing procedures for the appropriate staff.

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References 

  1. Adams BJ, Sukumvanich P, Seibel R, et al. Ultrasound for the detection of intraperitoneal fluid: the role of trendelenberg positioning. Am J Emerg Med. 1999;17:117–120
  2. American College of Emergency Physicians . Emergency ultrasound guidelines 2001. Ann Emerg Med. 2001;38:470–481
  3. American Institute of Ultrasound in Medicine. Official statement: training guidelines for physicians who evaluate and interpret diagnostic ultrasound examinations; 1997.
  4. Australasian College for Emergency Medicine. Policy document: credentialing for ED ultrasonography; 2000. URL: http://www.acem.org.au/open/documents/ultrasonography.htm.
  5. Australasian Trauma Society. Australasian Trauma Society position on credentialing for trauma ultrasound for trauma specialists; 1998. URL: http://www.atsoc.com.au/policy.htm.
  6. Blackbourne LH, Soffer D, McKenney MG, et al. Secondary ultrasound examination increases the sensitivity of the FAST exam in blunt trauma. J Trauma. 2004;57:934–938
  7. Bode PJ, Niezen RA, van Vugt AB, et al. Abdominal ultrasound as a reliable indicator for conclusive laparotomy in blunt abdominal trauma. J Trauma. 1993;34:27–31
  8. Boulanger BR, Brenneman FD, McLellan BA, et al. A prospective study of emergent abdominal sonography after blunt trauma. J Trauma. 1995;39:325–330
  9. Boulanger BR, McLellan BA, Brenneman FD, et al. Emergent abdominal sonography as a screening test in a new diagnostic algorithm for blunt trauma. J Trauma. 1996;40:867–874
  10. Branney SW, Wolfe RE, Moore EE, et al. Quantitative sensitivity of ultrasound in detecting free intraperitoneal fluid. J Trauma. 1995;39:375–380
  11. Dolich MO, McKenney MG, Varela JE, et al. 2576 ultrasounds for blunt abdominal trauma. J Trauma. 2001;50:108–112
  12. Goleetti O, Ghiselli G, Lippolis PV, et al. The role of ultrasonography in blunt abdominal trauma: results in 250 consecutive cases. J Trauma. 1994;36:178–181
  13. Gracias VH, Frankel HL, Gupta R, et al. Defining the learning curve for the focused abdominal sonogram for trauma (FAST) examination: implications for credentialing. Am Surg. 2001;67:364–368
  14. Healey MA, Simons RK, Winchell RJ, et al. A prospective evaluation of abdominal ultrasound in blunt trauma: is it useful. J Trauma. 1996;40:875–883
  15. Hoffman R, Nerlich M, Muggia-Sullam M, et al. Blunt abdominal trauma in cases of multiple trauma evaluated by ultrasonography: a prospective analysis of 291 patients. J Trauma. 1992;32:452–458
  16. Ingeman JE, Plewa MC, Okasinski RE, et al. Emergency physician use of ultrasonography in blunt abdominal trauma. Acad Emerg Med. 1996;3:931–937
  17. Jehle D, Guarino J, Karamanoukian H. Emergency department ultrasound in the evaluation of blunt abdominal trauma. Am J Emerg Med. 1993;11:342–346
  18. Jones P, Peak S, McClelland A, et al. Emergency ultrasound credentialing for focussed assessment sonography in trauma and abdominal aortic aneurysm: a practical approach for Australasia. Emerg Med. 2003;15:54–62
  19. Kern SJ, Smith RS, Fry WR, et al. Sonographic examination of abdominal trauma by senior surgical residents. Am Surg. 1997;63:669–674
  20. Lentz KA, McKenney MG. Letter to the editor. J Trauma. 1996;40:1052–1053
  21. Liu M, Lee CH, P’eng FK. Prospective comparison of diagnostic peritoneal lavage, computer tomographic scanning and ultrasonography for the diagnosis of blunt abdominal trauma. J Trauma. 1993;35:267–270
  22. McKenney MG, Martin L, Lentz K, et al. 1000 consecutive ultrasounds for blunt abdominal trauma. J Trauma. 1996;40:607–610
  23. McKenney MG, McKenney KL, Compton RP, et al. Can surgeons evaluate emergency ultrasound scans for blunt abdominal trauma. J Trauma. 1998;44:649–653
  24. Miller MT, Pasquale MD, Bromberg WJ. Not so fast. J Trauma. 2003;54:52–60
  25. Nunes LW, Simmons S, Hallowell MJ, et al. Diagnostic performance of trauma US in identifying abdominal or pelvic free fluid and serious abdominal or pelvic injury. Acad Radiol. 2001;8:128–136
  26. Rothlin MA, Naf R, Amgwerd M, et al. Ultrasound in blunt abdominal and thoracic trauma. J Trauma. 1993;34:488–495
  27. Royzycki GS, Ballard RB, Feliciano DV, et al. Surgeon-performed ultrasound for the assessment of truncal injuries: lessons learned from 1540 patients. Ann Surg. 1998;228:557–567
  28. Royzycki G, Ochsner MG, Jaffin J, et al. Prospective evaluation of surgeon's use of ultrasound in the evaluation of trauma patients. J Trauma. 1993;34:516–527
  29. Royzycki G, Ochsner MG, Schmidt JA, et al. A prospective study of surgeon-performed ultrasound as the primary adjuvant modality for injured patient assessment. J Trauma. 1995;39:492–500
  30. Scalea TM, Rodriguez A, Chiu WC, et al. Focussed assessment with sonography for trauma (FAST): results from an international consensus conference. J Trauma. 1999;46:466–472
  31. Shackford SR, Rogers FB, Osler TM, et al. Focused abdominal sonogram for trauma: the learning curve of nonradiologist clinicians in detecting hemoperitoneum. J Trauma. 1999;46:553–564
  32. Thomas B, Falcone RE, Vasquez D, et al. Ultrasound evaluation of blunt abdominal trauma: program implementation, initial experience, and learning curve. J Trauma. 1997;42:384–388
  33. Thomas B, Falcone RE, Vasquez D, et al. Ultrasound evaluation of blunt abdominal trauma: program implementation, initial experience, and learning curve. J Trauma. 1997;42:384–390
  34. Tso P, Rodriguez A, Cooper C, et al. Sonography in blunt abdominal trauma: a preliminary progress report. J Trauma. 1992;33:39–44
  35. Vassiliadis J, Edwards R, Larcos G, et al. Focussed assessment with sonography for trauma patients by clinicians: initial experience and results. Emerg Med. 2003;15:42–48

PII: S0020-1383(06)00130-6

doi:10.1016/j.injury.2006.03.004

Injury
Volume 38, Issue 1 , Pages 71-75, January 2007

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