Novices may be trained to screen for abdominal aortic aneurysms using ultrasound

Abstract

Background: Highly trained vascular sonographers make up a significant cost of abdominal aortic aneurysm (AAA) ultrasound screening. However, they are over-trained for this very limited task. Others have reported that health workers (e.g. emergency room staff and nurses) with far less training may be able to perform these scans. The national AAA screening programme in the UK uses staff with limited training. Whether individuals without a health professional qualification could be trained to perform the scan accurately to improve cost-effectiveness is not known. We aimed to investigate whether a short, well-supervised course in ultrasonography could train novices to detect AAA for screening purposes.

Methods: Three novices were trained by an experienced sonographer for 15 days to perform abdominal aortic ultrasound examinations and detect AAA using a portable ultrasound system. The examination included four anterior-posterior aortic measurements: a maximal diameter in the coronal plane and three diameters of the suprarenal, mid and distal infrarenal aorta in the transverse plane. The novices independently scanned 215 subjects following training; experienced sonographers repeated the measurements on the same subject in the same session. Using Bland-Altman plots and CUSUM analysis, the novices' and experienced sonographers' accuracy and efficiency measurements were compared. Factors influencing performance were recorded.

Results: The novices measured the maximal coronal aortic diameter accurately, to within 0.46-0.52 cm of the true diameter; 85-97% of their coronal measurements were within 0.5 cm of the assessors; kappa statistic and Bland-Altman plots show a high agreement with the assessor's measurements. However, the novices' measurements of the three diameters in the transverse plane were outside clinically acceptable limits. Assuming a referral policy for a second scan for scans recorded as 'difficult', only one novice missed a 3.13 cm aneurysm.A CUSUM quality improvement analysis demonstrated substantial improvements in the scanning efficiency of the novices with continued scanning experience.

Conclusion: This study showed that novices could be trained to screen for AAA over 15 days. However, the need for continuing quality improvement is critical, especially in more technically demanding cases. Measuring the maximal infrarenal diameter instead of specific segmental diameters may be more appropriate for AAA screening using novices.

Figure 1

Bland-Altman plots. Illustrating variations in performance. Bland-Altman graphs plot the inter-observer differences of the novice-assessors (y-axis) against the averages of those measurements. The dotted lines demarcate the limits of agreement (LOA), which should ideally lie within the clinically acceptable difference (CAD) of 0.5 cm. A demonstrates an acceptable performance by Novice 3 when measuring the maximal coronal diameter, with no measurement bias and the LOA within the CAD. B shows unacceptably high variability in Novice 1 measurements from mid-infrarenal aortic section with outliers in both normal and aneurysmal aorta. C shows a large under-sizing bias of 0.5 cm by Novice 1 when measuring the suprarenal segment of aortae, in addition the variability of measurement exceeded the CAD.

Figure 2

Cusum plots demonstrating the progression in scanning efficiency for each novice over the study period. The mean and SD were calculated from a sample of 220 scans with a 90% success rate, using 10,000 iterations in the bootstrapping procedure. Limit lines (dotted grey lines) demarcate when the success rate becomes higher or lower than would be expected if due to chance with 97.5% certainty. The criterion for a success was any scan completed within 10 min and is charted as an increase of 0.21 on the chart. Failure, results in a decrease on the plot of -1.79. Assessors have a higher success rate than 90% and cross the upper boundary limits at scans 56, 118, 171; Novice scanners have lower success rate than expected: Novice 1 crosses lower limits at scans 22, 39, 59, 83, 97,104, 173; Novice 2 crosses lower limits at scans 30, 44, 58, 90, 103; Novice 3 crosses lower limits at scan 81. After scan 110 a plateau in performance occurs in the novices performances.