Study designs of evaluations included in the review
Randomised controlled trials (RCTs), which were adequately powered where the results were statistically non significant, were eligible for inclusion. The studies had to be truly randomised and present information on ventilator circuit changes, filter changes, suction episodes, instillation of saline and physiotherapy sessions, so that it could be determined that the groups were treated equally apart from the interventions being compared. Details of eight excluded studies, including reasons for exclusion, were presented. Reasons for exclusion included insufficient data and inadequate validity.
Specific interventions included in the review
The inclusion criteria were not specified in terms of the interventions, but it was clear that studies comparing any type of heated humidifier with any type of HME device were included. The included studies compared an extended-use hygroscopic condenser humidifier with heated water humidification (Fisher and Paykel), and a Pall BB-100 (hydrophobic/hydrophilic media bacterial/viral filter) that was changed every 24 hours with an unspecified type of heated water humidifier. Both of the included studies were conducted in the USA and both studies excluded high-risk patients.
Participants included in the review
Studies of intensive care unit (ICU) patients were eligible for inclusion. The stated aim of the review indicated that intubated ICU patients who had been ventilated for more than 48 hours were the focus of the review, while the search strategy implied that only adult patients (older than 18 years) were eligible. The included studies were conducted in medical, surgical and trauma ICU patients. The mean age of the participants ranged from 47 years for trauma patients to 58.4 years for medical and surgical ICU patients.
Outcomes assessed in the review
Studies that presented data on tracheal tube occlusion or VAP were eligible for inclusion. The diagnosis of VAP was made using objective predefined criteria in one included study, and criteria modified from the American College of Chest Physicians in the other study. Complete tracheal occlusion was diagnosed clinically in one study, and using a scoring system to assess the relative degree of obstruction (greater than 50%, or 25 to 50% of the internal diameter) on extubation or during bronchoscopy in the other study.
One of the included studies followed up patients until successful weaning from the ventilator, or hospital discharge or death, while the other study followed up patients for 6 months.
How were decisions on the relevance of primary studies made?
The author alone selected studies for inclusion.