Comparison 1. US‐guided arterial cannulation versus other techniques (palpation/Doppler).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Successful cannulation at the first attempt	4	404	Risk Ratio (M‐H, Random, 95% CI)	1.96 [1.34, 2.85]
2 Successful cannulation at the first attempt as per age group	4	404	Risk Ratio (M‐H, Random, 95% CI)	1.96 [1.34, 2.85]
2.1 Older children	1	152	Risk Ratio (M‐H, Random, 95% CI)	1.01 [0.46, 2.24]
2.2 Infants and small children	3	252	Risk Ratio (M‐H, Random, 95% CI)	2.22 [1.62, 3.06]
3 Successful cannulation at the first attempt as per expertise with US usage	4	404	Risk Ratio (M‐H, Random, 95% CI)	1.96 [1.34, 2.85]
3.1 No expertise with ultrasound	2	256	Risk Ratio (M‐H, Random, 95% CI)	1.48 [0.72, 3.07]
3.2 Expertise with US usage	2	148	Risk Ratio (M‐H, Random, 95% CI)	2.25 [1.58, 3.19]
4 Rate of complications (haematoma or ischaemia)	2	222	Risk Ratio (M‐H, Fixed, 95% CI)	0.2 [0.07, 0.60]
5 Successful cannulation within the first 2 attempts	2	134	Risk Ratio (M‐H, Fixed, 95% CI)	1.78 [1.25, 2.51]
6 Rate of successful cannulation	2	70	Risk Ratio (M‐H, Random, 95% CI)	1.15 [0.95, 1.40]