Patient or population: adults undergoing peripheral venous cannulation classed as difficulta Settings: emergency department, ICU, operating room Intervention: USG Comparison: LM
Outcomes	Subgroups	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	No. of participants (studies)	Certainty of the evidence (GRADE)	Comments
		Risk with LM	Risk with USG
First‐pass success of cannulation   Follow‐up: immediately after the procedure	Emergency department	345 per 1000	552 per 1000 (386 to 787)	RR 1.60 (1.12 to 2.28)	546 (6 RCTs)	⊕⊝⊝⊝ Very lowb
	ICU	325 per 1000	533 per 1000 (390 to 724)	RR 1.64 (1.20 to 2.23)	234 (3 RCTs)	⊕⊕⊝⊝ Lowc
	Operating room	813 per 1000	739 per 1000 (512 to 1000)	RR 0.91 (0.63 to 1.30)	35 (1 RCT)	⊕⊕⊝⊝ Lowc
Overall success of cannulation   Follow‐up: immediately after the procedure	Emergency department	557 per 1000	874 per 1000 (585 to 1000)	RR 1.57 (1.05 to 2.36)	401 (6 RCTs)	⊕⊝⊝⊝ Very lowd
	ICU	547 per 1000	744 per 1000 (470 to 1000)	RR 1.36 (0.86 to 2.15)	234 (3 RCTs)	⊕⊝⊝⊝ Very lowe
	Operating room	1000 per 1000	1000 per 1000 (900 to 1000)	RR 1.00 (0.90 to 1.11)	35 (1 RCT)	⊕⊕⊝⊝ Lowc
Pain NRS: from 0, no pain to 10, maximum pain   Follow‐up: immediately after the procedure	Emergency department	The mean pain score was 4.0	MD 0.2 lower (1.13 lower to 0.72 higher)	‐	323 (4 RCTs)	⊕⊝⊝⊝ Very lowf
	ICU						No eligible studies
	Operating room						No eligible studies
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; ICU: intensive care unit; LM: landmark method; MD: mean difference; NRS: numerical rating scale; RCTs: randomised controlled trials; RR: risk ratio; USG: ultrasound guidance
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.