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	Operators had any clinical experience	361 per 1000	519 per 1000 (328 to 819)	RR 1.44 (0.91 to 2.27)	460 (5 RCTs)	⊕⊝⊝⊝ Very lowb
	Operators did not have any clinical experience	446 per 1000	594 per 1000 (442 to 799)	RR 1.33 (0.99 to 1.79)	235 (3 RCTs)	⊕⊕⊝⊝ Lowc
	Operators experience was not specified	183 per 1000	403 per 1000 (224 to 726)	RR 2.20 (1.22 to 3.96)	120 (2 RCTs)	⊕⊕⊝⊝ Lowd
Overall success of cannulation   Follow‐up: immediately after the procedure	Operators had any clinical experience	726 per 1000	835 per 1000 (661 to 1000)	RR 1.15 (0.91 to 1.44)	315 (5 RCTs)	⊕⊝⊝⊝ Very lowe
	Operators did not have any clinical experience	509 per 1000	743 per 1000 (601 to 911)	RR 1.46 (1.18 to 1.79)	235 (3 RCTs)	⊕⊝⊝⊝ Very lowf
	Operators experience was not specified	333 per 1000	693 per 1000 (470 to 1000)	RR 2.08 (1.41 to 3.09)	120 (2 RCTs)	⊕⊝⊝⊝ Very lowg
Pain NRS: from 0, no pain to 10, maximum pain   Follow‐up: immediately after the procedure	Operators had any clinical experience						Not performed due to insufficient number of studies
	Operators did not have any clinical experience						Not performed due to insufficient number of studies
	Operators experience was not specified						Not performed due to insufficient number of 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.