Cao 2018.

Study characteristics
Methods	Single‐centre prospective randomised controlled 2‐arm parallel‐assignment single‐blinded (outcomes assessor) study China Duration: December 2016 to May 2017.
Participants	120 participants randomised (experimental = 60, comparator = 60) 120 participants analysed mean age (years) ± SD: 51.9 ± 3.3 experimental, 52.3 ± 3.5 comparator gender (male/female): 28/32 experimental, 31/29 comparator severity of condition (experimental/comparator): all participants from the department of critical care medicine comorbidities (experimental/comparator): peripheral vascular disease 26/15 BMI (kg/m²) ± SD: 30 ± 8 experimental, 31 ± 7 comparator artery of interest: radial diameter (mm), mean ± SD: 2.8 ± 0.7 experimental, 2.9 ± 0.7, comparator. Catheter diameter 22 G catheterisation purpose (experimental/comparator): all for diagnosis (pressure monitoring) Inclusion criteria needing radial arterial cannulation Exclusion criteria peripheral vascular disease positive for Allen's test coagulopathy
Interventions	Experimental: ultrasound‐guided RA puncture (real‐time, artery short axis, needle out‐of‐plane) Comparator: RA puncture using palpation and landmarks Level of experience of person carrying out the procedure: quote: "nursing staff who have obtained the certificate of completion for critical care ultrasound" Concomitant medications: quote: "arterial cannulation was performed either before or after induction of general anesthesia based on the preference of the faculty anesthesiologist" Excluded medications: not reported
Outcomes	Primary (specified) first‐attempt success rate total success rate number of catheterisation attempts rate of complications time taken for entire procedure Primary (collected) first‐attempt success rate total success rate number of catheterisation attempts rate of complications time taken for entire procedure Secondary (specified) no differentiation between primary and secondary outcomes Secondary (collected) no differentiation between primary and secondary outcomes Time points reported: up to 5 minutes
Notes	Funding: quote: "this work was supported by the Research Fund of Health and Family Planning, Commission of Hunan Province, China (B2017012)" Conflicts of interest: not reported 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 interventions, we assumed that blinding of personnel is 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	Low risk	We do not suspect any other bias related to this study