Internal jugular vein Subclavian vein Femoral vein No of placements No of placements No of placements Variable 2-D ultrasound guidance Landmark method Effect size (95% CI) P value 2-D ultrasound guidance Landmark method Effect size (95% CI) P value Doppler ultrasound guidance Landmark method Effect size (95% CI) P value Adults Relative risk: Failed catheter placement 296 312 0.14 (0.06 to 0.33) <0.0001 25 27 0.14 (0.04 to 0.57) 0.006 20 20 0.29 (0.07 to 1.21) 0.09 Complication with placement 284 295 0.43 (0.22 to 0.87) 0.02 25 27 0.10 (0.01 to 0.71) 0.02 — — NA NA Failure on first attempt 162 179 0.59 (0.39 to 0.88) 0.009 — — NA NA — — NA NA Mean No: Attempts to successful catheterisation 131 136 -1.50 (-2.53 to -0.47) 0.004 — — NA NA 20 20 -2.70 (-5.26 to -0.14) 0.04 Seconds to successful catheterisation 180 192 -69.33 (-92.36 to -46.31) <0.0001 — — NA NA 20 20 -3.20 (-43.27 to 36.87) 0.9 Infants Relative risk: Failed placement 79 88 0.15 (0.03 to 0.64) 0.01 — — NA NA — — NA NA Complication with placement 79 88 0.27 (0.08 to 0.91) 0.03 — — NA NA — — NA NA Failure on first attempt — — NA NA — — NA NA — — NA NA Mean No: Attempts to successful catheterisation 43 52 -2.00 (-2.78 to -1.22) <0.0001 — — NA NA — — NA NA Seconds to successful catheterisation 59 68 -349.38 (-801.89 to 103.13) 0.13 — — NA NA — — NA NA

NA=not available. All outcomes favoured ultrasound guidance (relative risk <1).