Patient or population: adults undergoing peripheral venous cannulation classed as difficulta Settings: emergency department, ICU Intervention: USG Comparison: LM
Outcomes	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	339 per 1000	549 per 1000 (433 to 698)	RR 1.62  (1.28 to 2.06)	780 (9 RCTs)	⊕⊕⊕⊝ Moderateb
Overall success of cannulation   Follow‐up: immediately after the procedure	541 per 1000	828 per 1000 (606 to 1000)	RR 1.53  (1.12 to 2.08)	588 (8 RCTs)	⊕⊝⊝⊝ Very lowc
Pain NRS: from 0, no pain to 10, maximum pain   Follow‐up: immediately after the procedure	The mean pain score was 4.07	MD 0.49 lower (1.48 lower to 0.49 higher)	‐	305 (3 RCTs)	⊕⊝⊝⊝ Very lowd
Procedure time for first‐pass cannulation (seconds)   Follow‐up: immediately after the procedure	The mean procedure time for first‐pass cannulation was 137.8 seconds	MD 120.6 seconds longer (88.3 longer to 152.9 longer)	‐	192 (1 RCT)	⊕⊕⊕⊝ Moderatee
Number of cannulation attempts   Follow‐up: immediately after the procedure	The mean number of cannulation attempts was 2.20	MD 0.36 lower (0.75 lower to 0.03 higher)	‐	468 (6 RCTs)	⊕⊝⊝⊝ Very lowf
Patient satisfaction NRS from 0 to 10 or 4‐step Likert scale The higher the score, the higher the level of satisfaction Follow‐up: immediately after the procedure	The mean patient satisfaction score was 5.96	SMD 0.52 higher (0.01 lower to 1.05 higher)	‐	286 (4 RCTs)	⊕⊝⊝⊝ Very lowg
Overall complications   Follow‐up: immediately after the procedure	121 per 1000	78 per 1000 (45 to 133)	RR 0.64 (0.37 to 1.10)	431 (5 RCTs)	⊕⊕⊝⊝ Lowh
*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: numeric rating scale; RCTs: randomised controlled trials; RR: risk ratio; SMD: standardised mean difference; 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.