Parke 2013a.

Study characteristics
Methods	RCT, parallel‐group design. Single‐centre
Participants	Total number of randomized participants: 340 Setting: ICU; Auckland, New Zealand Inclusion criteria: undergoing elective cardiac surgery utilizing cardiopulmonary bypass were eligible for inclusion in this study if ≥ 18 years of age and undergoing surgery involving full median sternotomy Exclusion criteria: contraindication to HFNC, e.g. presence of a nasal septal defect, and previous recruitment Baseline characteristics: Intervention group (HFNC): Age, median (range): 65 (19 to 88) years Gender, M/F: 129/40 BMI, mean (SD): 28.4 (± 5.3) kg/m2 APACHE II, mean (SD): not reported PaCO2: not reported PaO2/FiO2: not reported Respiratory rate, mean (SD): 16.6 (± 1.9) breaths/min Control group (simple face mask): Age, median (range): 66 (21 to 87) years Gender, M/F: 129/42 BMI, mean (SD): 29.2 (± 5.5) kg/m2 APACHE II, mean (SD): not reported PaCO2: not reported PaO2/FiO2: not reported Respiratory rate, mean (SD): 16.5 (± 1.7) breaths/min
Interventions	Intervention group: Randomized, n = 170; losses, n = 1 (consent withdrawn); analysed, n = 169 Details: HFNC; Optiflow system; flow rate 45 L/min Control group: Randomized, n = 171; losses, n = 0; analysed, n = 171 Details: Simple face mask; oxygen at 2 to 4 L/min via simple face mask or nasal prongs; FiO2 in both groups was titrated to maintain SpO2 > 93%. Oxygen therapy started after extubation.
Outcomes	Number of participants with SpO2/FiO2 ratio ≥ 445 on day 3 after cardiac surgery; atelectasis score of chest X‐rays; spirometry; re‐admission to ICU for respiratory causes; ICU and hospital length of stay; duration of respiratory support; mortality; incidence of respiratory complications on day 28; respiratory rate; oxygenation; use of adjunctive respiratory support therapies; escalation of respiratory support; adverse events; patient comfort
Notes	Funding/declarations of interest: Study authors declared that research was supported by an unrestricted grant from Fisher & Paykel Healthcare Ltd, but that the sponsors had no part in the study design and no access to trial data. Study dates: not reported. Conducted over a 14‐month period Note: some additional outcome data retrieved through email contact with study authors
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated random numbers in blocks of 12
Allocation concealment (selection bias)	Low risk	Sequentially numbered opaque envelopes prepared by non‐study staff
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Blinding was not possible. Although we expected that this would not influence outcome data, we could not be certain of this.
Blinding of outcome assessors (objective outcomes)	Low risk	Blinding of outcome assessors was not described; we did not anticipate that this would influence the assessment of objective outcome measures.
Blinding of outcome assessors (subjective measures)	Low risk	Participants were outcome assessors for comfort scores: we did not expect blinding to influence the assessment of these outcome data.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Attrition fully reported. Small number of losses
Selective reporting (reporting bias)	High risk	ACTRN12610000973011. Prospective registration in November 2010. Published study reported additional outcomes that were not stated in trial registration records (ICU and hospital length of stay, duration of respiratory support, oxygenation, escalation of respiratory support, adverse events); this may indicate selective reporting bias for these outcomes.
Other bias	Low risk	We identified no other sources of bias.