MacIntyre 1983.

Methods	Randomized cross‐over study comparing HME to HH.
Participants	Inclusion criteria: clinically stable people requiring mechanical ventilation. Mean age: 60 years. Exclusion criteria: not stated. Respiratory diagnosis: 35%. Severity: not stated. Setting: hospital, USA.
Interventions	HME (hygroscopic): Servo humidifier. n = 26. HH: Puritan Bennett. n = 26. Time in study: 24 hr for each type of humidification.
Outcomes	PaCO2. Tracheal aspirations. * * Not considered valid because of the cross‐over design and, therefore, not used.
Notes	Funding: not stated.
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)	Unclear risk	No protocol available.
Other bias	Low risk	None identified.