Patient or population: adults undergoing peripheral venous cannulation classed as moderately difficulta Settings: emergency department, prehospital setting 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	733 per 1000	857 per 1000 (798 to 923)	RR 1.17 (1.09 to 1.26)	791 (3 RCTs)	⊕⊕⊕⊕ High
Overall success of cannulation Follow‐up: immediately after the procedure	904 per 1000	967 per 1000 (849 to 1000)	RR 1.07 (0.94 to 1.23)	436 (3 RCTs)	⊕⊝⊝⊝ Very lowb
Pain NRS: from 0, no pain, to 10, maximum pain Follow‐up: immediately after the procedure	The mean pain score was 2.96	MD 0.03 higher (0.43 lower to 0.48 higher)	‐	491 (2 RCTs)	⊕⊕⊝⊝ Lowc
Procedure time for first‐pass cannulation (seconds) Follow‐up: immediately after the procedure	The mean procedure time for first‐pass cannulation was 100.6 seconds	MD 23.0 seconds longer (39.9 shorter to 85.9 longer)	‐	749 (3 RCTs)	⊕⊝⊝⊝ Very lowd
Number of cannulation attempts Follow‐up: immediately after the procedure	The mean number of cannulation attempts was 1.51	MD 0.32 lower (0.47 lower to 0.16 lower)	‐	437 (3 RCTs)	⊕⊕⊕⊝ Moderatee
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 7.63	SMD 0.08 higher (0.51 lower to 0.66 higher)	‐	137 (2 RCTs)	⊕⊝⊝⊝ Very lowf
Overall complications Follow‐up: immediately after the procedure	131 per 1000	76 per 1000 (43 to 133)	RR 0.58 (0.33 to 1.02)	791 (3 RCTs)	⊕⊕⊝⊝ Lowg
*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; LM: landmark method; MD: mean difference; NRS: numeric 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.