Tangwiwat 2016.

Study characteristics
Methods	Single‐centre prospective randomised controlled 2‐arm study, with blinding not described Thailand Duration: November 2009 to October 2010
Participants	100 participants randomised (experimental = 30, comparator = 30) 100 participants analysed mean age (years) ± SD: 51.0 ± 15.3 experimental, 50.4 ± 15.1 comparator gender (male/female): 20/30 experimental, 19/31 comparator severity of condition (experimental/comparator): all participants undergoing neurosurgery, ASA 1 (4/3), ASA 2 (36/41), ASA 3 (10/6) comorbidities (experimental/comparator): number of patients intubated 22/23 body weight (kg): not reported height (cm): not reported artery of interest: radial diameter (mm), mean ± SD: not reported. Catheter size 20 G catheterisation purpose (experimental/comparator): all for diagnosis (pressure monitoring or blood test, % not reported, during neurosurgery) Inclusion criteria undergoing neurosurgery >18 years old indication for radial artery cannulation Exclusion criteria pregnant women negative modified Allen’s test severe vascular morbidity such as limb ischaemia from multiple insertion attempts and air emboli
Interventions	Experimental: ultrasound‐guided RA puncture (real‐time, artery short axis, out‐of‐plane) Comparator: RA puncture by palpation and landmarks Level of experience of person carrying out the procedure: quote: "ten third‐year residents, having performed USG vascular catheterization as yet less than 3 times" Concomitant medications: not reported Excluded medications: not reported
Outcomes	Primary (specified) time to placement number of attempts sites used success rate complications (haematoma, infection, retained catheter, radial nerve damage, arterial thrombosis/ischaemia, carpal tunnel syndrome) Primary (collected) success rate in first attempt time to placement number of attempts sites used success rate complications (haematoma) Secondary (specified) no differentiation between primary and secondary outcomes Secondary (collected) no differentiation between primary and secondary outcomes Time points reported: up to 24 hours
Notes	Funding: quote: "this work was supported by Siriraj Research Development Fund, Faculty of Medicine Siriraj Hospital, Mahidol University" Conflicts of interest: quote: "none" Protocol not available
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "using computer generated block randomization (mixed block size)"
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	High risk	There was an imbalance in cross‐over interventions between experimental (6/50) and comparator (1/50) groups
Selective reporting (reporting bias)	High risk	Some of the planned safety outcomes were not reported (infection, retained catheter, radial nerve damage, arterial thrombosis/ischaemia, carpal tunnel syndrome)
Other bias	Low risk	We do not suspect any other bias related to this study