Kim 2021a.

Study characteristics
Methods	Single‐centre prospective randomised controlled 2‐arm parallel‐assignment open‐label study Korea Duration: 3 March 2017 to 16 November 2017
Participants	76 participants randomised 76 analysed (experimental = 38, comparator = 38), losses not described mean age (years) ± SD: 52.5 ± 15.0 experimental, 50.6 ± 14.1 comparator gender (male/female): 14/24 experimental, 21/17 comparator severity of condition: requiring clinically indicated arterial cannulation, under general anaesthesia comorbidities: not reported BMI (kg/m²): not reported artery of interest: radial diameter (cm), mean ± SD: 3.43 ± 1.23 experimental, 3.57 ± 1.07 comparator catheterisation purpose (experimental/comparator): all for diagnosis (not detailed) Inclusion criteria adults over 19 years of age required to have an arterial line insertion Exclusion criteria vascular malformation haemodynamically unstable blood coagulation disorder peripheral arterial occlusive disease reoperation emergency surgery
Interventions	Experimental: short‐axis, out‐of‐plane, B‐mode, real‐time ultrasound‐guided puncture Comparator: short‐axis, out‐of‐plane, B‐mode, real‐time ultrasound‐guided puncture plus electromagnetic guidance Level of experience of person carrying out the procedure: quote: "arterial cannulation was performed by a single anaesthesiologist who had successfully performed arterial cannulation under electromagnetic ultrasound guidance more than 50 times" Concomitant medications: all under general anaesthesia Excluded medications: not reported
Outcomes	Primary (specified) percentage of success and vascular wall puncture Primary (collected) percentage of success and vascular wall puncture Secondary (specified) adverse events Secondary (collected) first‐attempt success rate puncture site  cannulation time (seconds) number of attempts  posterior wall puncture haematoma thrombosis Time points reported: up to 1 day
Notes	Funding: quote: "this study was carried out with our departmental funding source. There was no other source of funding except our departmental funding source" Conflicts of interest: quote: "the authors declare that they have no competing interests" Protocol available (KCT0002476)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "the participants were randomly allocated into two groups using a computerized, randomized table"
Allocation concealment (selection bias)	Low risk	Quote: "the allocations were concealed in sequentially numbered, sealed, opaque envelopes"
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "the provider could not be blinded because the activation of the electromagnetic guidance system was displayed on the screen"
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