Ishii 2013.

Study characteristics
Methods	RCT
Participants	Number: 118 radial arteries Number per intervention Ultrasound: 59 radial arteries Palpation: 59 radial arteries Inclusion criteria Infants and small children Weight 3–20 kg Exclusion criteria Skin erosions or haematomas at or near the insertion site Visible recent catheterisation scars Prominent differences in arterial pressure between left and right arms Surgery/setting: elective cardiac surgery for congenital heart disease Baseline characteristics: Median age: 18.4 months (range 7–28) Median weight: 8.1 kg (range 6.04–10.48) Sex ratio: not reported
Interventions	Randomisation: right and left radial arteries were randomly assigned to cannulation by the ultrasound‐guided technique (ultrasound group) or the usual palpation technique (palpation group) via the envelope method. The ultrasound‐guided group included 28 right and 31 left radial arteries, whereas the palpation‐guided group included 31 right and 28 left radial arteries. Intervention: US usage (SonoSite, Bothell, WA, USA) with a 2‐ to 7‐MHz linear array transducer in real time using short axis. Control: palpation using the pulsation of the radial artery. Co‐intervention: non‐invasive electrocardiogram, pulse oximetry and blood pressure monitoring. After induction of general anaesthesia, cannulation was attempted with standard 24‐G JELCO cannulas (Smith's Medical, Dublin, OH, USA). A pillow was placed under the wrist to keep the arm slightly extended. The insertion site was disinfected, and no local anaesthetic was used. Experience of operator: trainees in anaesthesiology with > 3 years of clinical training and familiar with the ultrasound‐guided technique for central venous catheterisation in adults and children.
Outcomes	Primary study endpoints Rate of successful cannulation on first attempt Success rate after 3 attempts Secondary study endpoints Time to identification of the artery Overall number of cannulation attempts Incidence of complications
Notes	No information was provided regarding funding. Dr Sawa received royalties from The Reagents from the University of California. The remaining study authors disclosed that they had no potential conflicts of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The right and left radial arteries were randomly assigned to cannulation by the ultrasound‐guided technique (ultrasound group) versus the usual palpation technique (palpation group), using the envelope method."
Allocation concealment (selection bias)	Low risk	Quote: "The right and left radial arteries were randomly assigned to cannulation by the ultrasound‐guided technique (ultrasound group) versus the usual palpation technique (palpation group), using the envelope method."
Blinding of participants and personnel (performance bias) All outcomes	High risk	All participants underwent induction of general anaesthesia before arterial line cannulation (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "The procedure was classified as successful when the artery was cannulated and an arterial waveform was recorded."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Data available for all randomised participants.
Selective reporting (reporting bias)	Low risk	All outcomes were reported.
Other bias	Low risk	We identified no other sources of bias.