Summary of findings 2. Ultrasound guidance versus landmark method for peripheral venous cannulation in adults classed as moderately difficult.

Patient or population: adults undergoing peripheral venous cannulation classed as moderately difficulta Settings: emergency department 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	714 per 1000	813 per 1000 (728 to 906)	RR 1.14 (1.02 to 1.27)	401 (1 RCT)	⊕⊕⊕⊝ Moderateb
Overall success of cannulation Follow‐up: immediately after the procedure	See comment	‐	‐	‐	‐	None of the studies included moderately difficult participants
Pain NRS: from 0 to 10, where 10 is maximum pain  Follow‐up: immediately after the procedure	The mean pain score was 3.20	MD 0.10 higher (0.47 lower to 0.67 higher)		401 (1 RCT)	⊕⊕⊝⊝ Lowc
Procedure time for first‐pass cannulation (seconds) Follow‐up: immediately after the procedure	The mean procedure time for first‐pass cannulation was 122.6 seconds	MD 95.2 seconds longer (72.8 longer to 117.6 longer)		401 (1 RCT)	⊕⊕⊕⊕ High
Number of cannulation attempts Follow‐up: immediately after the procedure	See comment	‐	‐	‐	‐	None of the studies included moderately difficult participants
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	See comment	‐	‐	‐	‐	None of the studies included moderately difficult participants
Overall complications Follow‐up: immediately after the procedure	65 per 1000	54 per 1000 (25 to 119)	RR 0.83 (0.38 to 1.82)	401 (1 RCT)	⊕⊕⊕⊝ Moderated
*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; 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.

^aParticipants were classified according to the original studies' definitions.
^bWe downgraded by one level to moderate certainty due to imprecision.
^cWe downgraded by a total of two levels to low certainty due to risk of bias concerns (lack of blinding of the outcome assessors) and imprecision.
^dWe downgraded by one level to moderate certainty due to imprecision.