INTRA- OR INTER-OBSERVER VARIATION

Beales et al. systematically reviewed studies on intra- or inter-observer variations in ultrasound measurements {21}. The acceptable level of observer variation between aortic diameter measurements was suggested to be 5 mm. From the nine studies evaluated, five o presented coefficients lower that this limit. The most relevant factors they found that could affect reproducibility were: observer´s experience level, patient´s obesity and bowel gas, aortic diameter, and whether the machine was modern.

Singh et al. assessed the agreement between ultrasound and computed tomography measurements of normal and aneurysmatic aorta and the common iliac artery diameter {22}. After evaluating 3686 measurement pairs from 555 patients, they found considerable disagreement between the two techniques. Ultrasound underestimated aortic diameter in measurements of normal sized aortas (<30 mm) as compared with CT, whereas the opposite was true for aneurysmal aortas.

Singh et al. examined in an additional study the intra and inter-observer variability of CT measurements in 59 individuals. The authors found that approximately 95% of the CT measurements of the maximal infrarenal aortic diameter of the abdominal aorta could be performed with accuracy within the limit of 4 mm. The intra-observer variability for both planes was less than inter-observer variability, was increased with increasing vessel diameter, and was influenced by the experience level of the radiologist.

VOLUME–OUTCOME RELATIONSHIP

A systematic review that examined both open and endovascular repair of intact AAA found that hospital volume, surgeon volume, and surgeon´s specialisation in vascular surgery were all significant and highly associated with mortality {23}. Regarding hospital volume, a meta-analysis of 421,229 elective AAA repairs resulted in a pooled OR of mortality for high-volume institutions (≥43 OAR per annum) of 0.66 (95% CI: 0.65-0.67) as compared with low-volume institutions (<43 OAR per annum) {24}.

A meta-analysis evaluating 115,273 AAA repairs found that repairs by high-volume surgeons resulted in a decreased mortality compared with those by low-volume surgeons (pooled OR: 0.56; 95% CI 0.54-0.57), suggesting a threshold of 13 AAAs surgical repairs per year {25}. Surgeon volume had more effect than did hospital volume in a study of 5972 OARs after adjusting for other patient and hospital characteristics {26}. However, neither surgeon nor hospital volumes were found to have a significant influence on mortality after EVARs {26}.

Surgeon specialty, which implies subspecialty training and board certification, was also identified as influencing outcomes in AAA repair {27-29}. Operations performed by vascular specialist surgeons were associated with significant reductions in mortality compared with those done by general surgeons.

INCREASED BURDEN ON SURGICAL SERVICES

There is evidence that AAA screening causes an increased burden on local vascular surgical services; however its consequence on health outcomes has not been assessed. Among the 67,770 men recruited in the MASS trial, and after 10 years of follow-up, 552 elective operations took place in the invited group (n=33,883) and 226 in the control group (n=33,887). Sixty-two men underwent emergency surgery in the invited group compared with141 in the control group. These data show that the rate of elective repairs doubles with the advent of screening, and emergency ruptures are reduced by half {30}.