McCarthy 2016A.

Study characteristics
Methods	Randomised, open‐label trial
Participants	Setting: ED Number of participants: 192 (USG 98, LM 94) Age, mean (SD) years: not specified Difficulty: difficult (could not see or palpate a vein) Sites of peripheral veins: upper extremity
Interventions	Technique LM vs USG: Machine: Sonosite M‐Turbo (Sonosite) or Zonare ultra (Zonare) Axis: not specified Guidance: dynamic Operator Profession: technician Number of operators: 33 Experience of USG before the study: yes Length of experience with USG before the study: 82% of the operators had more than one year of experience A training programme of USG for the study: yes Number of clinical cases with USG required or experienced before the study intervention started: not specified Needle Length: 32 or 48 mm Gauge: 18 ‐ 22
Outcomes	First‐pass success of cannulation, procedure time for first‐pass cannulation, pain, complications Definition of successful cannulation: smooth normal saline flush, and no signs of extravasation Definition of start and end of time measurement Start: tourniquet placement End: saline solution flush through a peripheral intravenous line
Funding	Award K01HS017957 from the Agency for Healthcare Research and Quality
Declarations of interest	None declared
Notes	McCarthy 2016 randomised participants separately according to the difficulty of the LM (easy, moderate, and difficult), and we split them according to the difficulty level (McCarthy 2016A; McCarthy 2016B; McCarthy 2016C)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The randomisation scheme was created by SAS software (version 9.3; SAS Institute Inc, Cary, NC)
Allocation concealment (selection bias)	Low risk	Centrally randomised with REDCap (version 6.5.12; Nashville, TN)
Blinding (performance bias and detection bias) First‐pass success of cannulation	Low risk	Although blinding of participants and operators is impossible due to the nature of the intervention, a third person assessed the outcome
Blinding (performance bias and detection bias) Pain	High risk	Although a third person assessed the outcome, participants were not blinded and the outcome could be influenced by subjectivity
Blinding (performance bias and detection bias) Procedure time for first‐pass cannulation	Low risk	Although blinding of participants and operators is impossible due to the nature of the intervention, a third person assessed the outcome
Blinding (performance bias and detection bias) Overall complications	Low risk	Although blinding of participants and operators is impossible due to the nature of the intervention, a third person assessed the outcome
Incomplete outcome data (attrition bias) First‐pass success of cannulation	Low risk	There were only two dropouts (USG 1, LM 1)
Incomplete outcome data (attrition bias) Pain	Low risk	There were only 4 dropouts out of 1189 participants across the whole study
Incomplete outcome data (attrition bias) Procedure time for first‐pass cannulation	Low risk	There were only 7 dropouts out of 1189 participants across the whole study
Incomplete outcome data (attrition bias) Overall complications	Low risk	The outcome was available for all participants
Selective reporting (reporting bias)	Low risk	The outcomes reported in the article were consistent with the trial registry (NCT01859559)
Other bias	Low risk	No concerns about other sources of bias
Overall risk First‐pass success of cannulation	Low risk	All domains were at low risk
Overall risk Pain	High risk	At least one domain was at high risk
Overall risk Procedure time for first‐pass cannulation	Low risk	All domains were at low risk
Overall risk Overall complications	Low risk	All domains were at low risk