Cao 2020.

Study characteristics
Methods	[Preprint] Single‐centre prospective randomised controlled 3‐arm parallel‐assignment open‐label study China Duration: 1 April 2020 until 28 July 2020
Participants	216 participants randomised (number for each group not reported) 201 analysed (experimental (LA/in‐plane) = 63, comparator (SA/out‐of‐plane) = 70, comparator (OA/in‐plane) =  68), losses not described mean age (years) ± SD: 52 ± 10 (experimental), 50 ± 12 (comparator SA), 51 ± 13 (comparator OA) gender (male/female): 34/29 (experimental), 32/38 (comparator SA), 33/35 (comparator OA) severity of condition: patients who required continuous pressure monitoring during elective surgery comorbidities: not mentioned BMI (kg/m²): 25 ± 4 (experimental LA), 25 ± 4 (comparator SA), 24 ± 3 (comparator OA) artery of interest: radial diameter (cm), mean ± SD: 22 ± 4 (experimental LA), 21 ± 4 (comparator SA), 20 ± 3 (comparator OA) catheterisation purpose (experimental/comparator): all for diagnosis (pressure monitoring) Inclusion criteria ASA status I to III who required continuous arterial pressure monitoring during scheduled surgery both sexes aged 40 to 65 years BMI 20 to 35 kg/m² Exclusion criteria inflamed skin near puncture site skin colour not returning to normal within 10 seconds after Allen's test abnormal coagulation function peripheral arterial disease recent arterial puncture < 1 month earlier hypertension and diabetes emergency surgery
Interventions	Experimental: LA, in‐plane, B‐mode, real‐time; quote: "probe was placed parallel to the course of the artery, and the needle was directed parallel to the longitudinal axis of the probe" Comparator: SA, out‐of‐plane, B‐mode, real‐time; quote: "the probe was placed perpendicular to the course of the artery, and the needle was directed perpendicular to the longitudinal axis of the probe" Comparator: OA, in‐plane, B‐mode, real‐time; quote: "the probe was positioned transversely perpendicular to the artery as in the SAX group and then rotated clockwise in situ by 60° according to maximum visualization" Level of experience of person carrying out the procedure: all participants were trained by a teacher who was familiar with the 3 approaches; they were "anaesthesia residents with no more than one year of experience in blind palpation for radial artery cannulation and who previously performed ultrasound‐guided radial artery cannulation fewer than five times in patients" Concomitant medications: not reported Excluded medications: not reported
Outcomes	Primary (specified) successful rate of catheterisation Primary (collected) successful arterial cannulation Secondary (specified) puncture blood return time catheterisation time adverse reaction Secondary (collected) first‐attempt success time needed for successful arterial cannulation cannulation failure (longer than 5 minutes and presence of a non‐arterial waveform) incidence of adverse events ‐ local haematoma and ischaemia Time points reported: not mentioned
Notes	Funding: quote: "none" Conflicts of interest: quote: "the authors declare that they have no competing interest" Protocol available (ChiCTR200030416)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "the patients were assigned by a randomized block design to three groups. We allocated patients at a 1:1:1 ratio with a computer‐generated list of random numbers in blocks of three, with the results accessible to only research nurses"
Allocation concealment (selection bias)	Low risk	Quote: "the sealed envelopes were opened immediately before the procedure"
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	Low risk	Quote: "with the results accessible to only research nurses"
Incomplete outcome data (attrition bias) All outcomes	High risk	There are losses (15 participants; 6.9%) that were not described regarding motivation or proportion among groups
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