Edanaga 2012.

Study characteristics
Methods	Single‐centre prospective randomised controlled 3‐arm parallel‐assignment study; blinding not reported Japan Duration: not reported
Participants	36 participants randomised (experimental = 24 (short axis = 12, long axis = 12), comparator = 12) 36 participants analysed mean age (years) ± SD: 70.45 ± 9.8 experimental, 68.5± 7.2 comparator gender (male/female): not reported severity of condition (experimental/comparator): not reported comorbidities (experimental/comparator): not reported body weight (kg) ± SD: 61 ± 10.79 experimental, 62.8 ± 10.8 comparator height (cm) ± SD: 161.1 ± 9.81 experimental, 164.5 ± 7.1 comparator artery of interest: radial diameter (mm), mean ± SD: not reported. Catheter diameter 22 G catheterisation purpose (experimental/comparator): all for diagnosis (pressure monitoring) Inclusion criteria negative for Allen's test Exclusion criteria not reported
Interventions	Experimental: ultrasound‐guided RA puncture (real‐time, artery short axis (N = 12) and long axis (N = 12), needle plane not reported) Comparator: RA puncture via palpation and landmarks Level of experience of person carrying out the procedure: anaesthesiologist staff have performed all punctures Concomitant medications: not reported Excluded medications: not reported
Outcomes	Primary (specified) number of catheterisation attempts Primary (collected) number of catheterisation attempts Secondary (specified) no differentiation between primary and secondary outcomes Secondary (collected) no differentiation between primary and secondary outcomes Time points reported: up to the end of the procedure (not described)
Notes	Funding: not reported Conflicts of interest: study authors declared no conflicts of interest Protocol not available
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not described, but due to the nature of the interventions, we assumed that blinding of personnel was not possible
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not described
Incomplete outcome data (attrition bias) All outcomes	Low risk	There were no losses
Selective reporting (reporting bias)	Low risk	All prespecified outcomes were reported
Other bias	High risk	Study did not evaluate any safety outcome