Number of failed catheter placements: 8 RCTs (513 placements and 493 patients).
Catheter placement complications: 7 RCTs (486 placements and 466 patients).
Number of attempts before success: 4 RCTs (303 placements and 303 patients).
Time to success: 5 RCTs (376 placements and 376 patients).
Number of failures: pooled RR in favour of ultrasound guidance was 0.32 (95% CI: 0.18, 0.55).
Complications during placement: RR in favour of ultrasound guidance was 0.22 (95% CI: 0.10, 0.45).
Number of attempt before success: RR in favour of ultrasound guidance was 0.60 (95% CI: 0.45, 0.79).
Time to success: the mean difference in the number of seconds until successful catheter placement using ultrasound guidance, compared to the landmark technique, was 9 seconds (95% CI: -80.1, 62.2).
The tests for heterogeneity were non significant in all analyses except among trials comparing time to catheter placement.