Five studies (n=1,909) were included: four single centric and one multicentric. Four were before-and-after studies and one was a prospective non-randomised controlled trial. All were considered to be of poor methodological quality. There was significant clinical heterogeneity among the included studies.
Three studies showed significant reduction in failure rates with the use of ultrasound. Pooling of the data from all the five studies showed significant reduction in failure rates with the ultrasound group (RR 0.40, 95% CI: 0.33 to 0.48); there was no evidence of statistical heterogeneity.
Pooling of the data from the three USA studies showed significant benefit of using ultrasound (RR 0.39, 95% CI: 0.33 to 0.47), but with significant statistical heterogeneity. The random-effects model showed a significant benefit of ultrasound (RR 0.35, 95% CI: 0.23 to 0.54). The UK studies showed no significant benefit (RR 0.52, 95% CI: 0.26 to 1.03).