Comparison 8. Overall complications.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
8.1 Difficulty levels defined by original studies	9	1818	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.46, 1.14]
8.1.1 Difficult	5	431	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.37, 1.10]
8.1.2 Moderate	1	401	Risk Ratio (M‐H, Random, 95% CI)	0.83 [0.38, 1.82]
8.1.3 Easy	1	596	Risk Ratio (M‐H, Random, 95% CI)	2.48 [0.90, 6.87]
8.1.4 No restriction by intravenous access difficulty level	2	390	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.24, 0.96]
8.2 Difficulty levels defined by the success rate with the landmark method	9	1818	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.46, 1.14]
8.2.1 Difficult	5	431	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.37, 1.10]
8.2.2 Moderate	3	791	Risk Ratio (M‐H, Random, 95% CI)	0.58 [0.33, 1.02]
8.2.3 Easy	1	596	Risk Ratio (M‐H, Random, 95% CI)	2.48 [0.90, 6.87]