Boots 1997.

Methods	Randomized parallel study comparing HME to HH.
Participants	Inclusion criteria: all admissions to general ICU requiring mechanical ventilation for > 48 hr. Mean age: 51 years. Exclusion criteria: people with asthma, airway burns or pulmonary haemorrhage. Respiratory diagnosis: respiratory failure: HME 38/42, HH 37/41. Mean APACHE II score: HME 19, HH 18. Setting: adult ICU, Australia.
Interventions	HME (hygroscopic): Humid‐Vent (Gibeck) changed every 24 hr. n = 42. HH (heated wire): MR730 (Fisher & Paykel) set at 37 ºC. n = 41. Change of circuit every 48 hr in both groups. Time in study (median): HME 6 days, HH 6 days.
Outcomes	Artificial airway occlusion. Mortality. VAP. Minute ventilation. Number of aspirations per hr ‐ no SD. Volume of secretions per hr ‐ no SD. Cost ‐ no SD.
Notes	Funding: Teleflex, Wayne, PA.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated.
Allocation concealment (selection bias)	Unclear risk	Not stated.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not stated.
Incomplete outcome data (attrition bias) All outcomes	Low risk	100% follow‐up.
Selective reporting (reporting bias)	Low risk	Protocol not available but all primary outcomes reported.
Other bias	Low risk	None identified.