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Three Part Question

In [patients suspected of having abdominal aortic aneurysms] is [ED bedside ultrasound performed by EM physicians as good as that performed by radiologists] at[accurately detecting AAA?]

Clinical Scenario

A 55-year-old man presents to the emergency department with a sudden onset of abdominal and flank pain associated with hypotension. Our concern is that he may have an AAA, but at this time the patient is too unstable to leave the emergency department for formal imaging. The vascular surgeons suggest a bedside ultrasound study. We perform one scan and see no AAA. Can you be confident that an ultrasound scan performed by an emergency physician can accurately rule in or out an AAA?

Search Strategy

Medline 1966–week 3 July 2006 using the Ovid interface, and
Embase 1980–weel 29 2006 using Multifile searching, and
Cochrane Library Issue 3 2006.
Medline/Embase: [(exp aortic aneurysm, abdominal/ultrasonography) and (exp emergency.mp. or emergencies/)]. LIMIT to human and English.
Cochrane Library: Aortic Aneurysm, Abdominal/US [MeSH] and Emergencies [MeSH] 0 records.

Search Outcome

A total of 73 papers were found, of which 69 were irrelevant
or of insufficient quality. The table summarises the contents of
remaining four papers.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Kuhn et al, 2000, Australia	Patients in whome AAAs were expected, including those patients over 50 years old presenting with abdominal/back pain of unclear origin or presumed renal colic ED bedside ultrasound preformed by EM physician who had attended a 3 day ultrasound training course.	Diagnostic cohort	Positive for AAA defined as aortic diameter > 3 cm.	68 patients scanned, aorta visualised in 66. 26 true positives and 40 true negatives. Sensitivity=100%, Specificity=100%, PPV=100%,NPV=100%	Small study, only 68 participants. Convenience sampling may have led to bias in selecting patients that are easier to scan or who have high clinical suspicion of AAA
			Improvement of patient care.	Improved care in 46 patients, 0 adversely affected
Tayal et al, 2003, USA	All patients suspected of having AAA. Emergency bedside ultrasound performed by EM physicians followed by a confirmatory test, i.e. radiology ultrasound, abdominal CT, abdominal MRI and laparotomy.	Diagnostic cohort	Positive or negative for AAA defined as abdominal aorta diameter > 3 cm	29/125 scans positive for AAA. 27/29 positive on confirmatory test. Sensitivity=100%, Specificity=98%, NPV=100%, PPV=93%	Small number of patients. Lack of clear inclusion and excusion criteria may have led to selection bias.
Knaut et al, 2005, USA	Convenience sample of patients 50 years and older with abdominal pain and scheduled for abdominal and pelvic CT scan with IV contrast as part of their evaluation. Ultrasound to measure the diameter of the abdominal aorta by either a resident or attending emergency medicine physician.	Diagnostic cohort	AAA diagnosed by ultrasound and confirmed by CT.	5/104 diagnosed by US were confirmed by CT. No false negatives. PPV of 0.00 at SMA, 0.67 in longitudinal view and 0.80 at bifurcation. NPV .099, 0.99, and 1.00 respectively	Convenience sample could lead to selection bias. Did not include patients that went to OR for repair that were not scanned.
			Difference in measured diameter at SMA, bifurcation and longitudinal view.	<1.41 cm at SMA, < 1.05 at bifurcation and <0.94 in longitudinal view 95 % of the time
Constantino et al, 2005, USA	Patients 55 and over with at least one of the following: abdominal, back, flank or chest pain or hypotension as well as clinical suggestion of AAA EUS performed by 3rd year EM residents	Diagnostic cohort	AAA measuring >3.0 cm on ultrasound.	36/238 had abnormal aortas, 34 AAA, 1 aortic dissection, 1 intraluminal clot. Sensitivity 100% for aortic abnormality, 94% for AAA. Specificity 100% for both endpoints.	Possible selection bias. Residents that performed EUS may have had more extensive training than most.

Comment(s)

Although all of these studies likely had some degree of selection bias, these are the patients that are most likely to benefit from early detection of AAA. It would have been helpful if they would have included information on patients that may have been excluded because of body habitus or potential difficulty in scanning. The amount of training in ultrasound does not seem to affect the accuracy.

Clinical Bottom Line

In patients suspected of having AAA, ED bedside ultrasound scanning for AAA is sensitive and specific and may improve patient care.

References

1. Kuhn, M. Bonnin, R. Davey, M et al. Emergency Department Ultasound Scanning for Abdominal Aortic Aneurysm: Accessible, Accurate and Advantageous. Annals of Emergency Medicine September 2000;36:219-223.
2. Tayal, V. Graf, C. Gibbs, M. Prospective study of Accuracy and Outcome of Emergency Deparment Ultrasound for Abdominal Aortic Aneurysm over Two Years. Academic Emergency Medicine August 2003;10:867-871.
3. Knaut, A. Kendal, J. Patten, R et al. Ultrasonographic Measurement of Aortic Diameter by Emergency Physicians Approximates Results Obtained by Computed Tomography. Journal of Emergency Medicine February 2005;28:119-126.
4. Constantino, T. Bruno, E. Handly, N et al. Accuracy of Emergency Medicine Ultrasound in the Evaluation of Abdominal Aortic Aneurysm. Journal of Emergency Medicine 2005;29:455-460.