Prospective randomised unblinded comparison of sputum viscosity for three methods of saline nebulisation in mechanically ventilated patients: a study protocol

Abstract

Background Heat and moisture exchanger (HME) filters are commonly used as passive circuit humidifiers during mechanical ventilation, however, are only ~ 80% efficient. As a result, patients that undergo mechanical ventilation in critical care with HME filter circuits will be exposed to partial airway humidification. This is associated with detrimental effects including increased secretion load which has been shown to be an independent predicter of failed extubation and poor outcome. Nebulised normal saline is commonly utilised to supplement circuit humidification in ventilated patients with high secretion loads, although there are no randomised control trials evaluating its use in critical care. Novel vibrating mesh nebulisers generate a fine aerosol resulting in deeper lung penetration, potentially offering a more effective means of nebulising normal saline in comparison to jet nebulisers. The primary aim of this study is to compare the viscosity of respiratory secretions after treatment with nebulised normal saline administered via vibrating mesh nebuliser or jet nebuliser. Methods This randomised controlled trial is enrolling 60 mechanically ventilated adult critical care patients breathing on HME filter circuits with high secretion loads. Recruited patients will be randomised to receive nebulised saline via 3 modalities: 1) Continuous vibrating mesh nebuliser; 2) Intermittent vibrating mesh nebuliser or 3) Intermittent jet nebuliser. Over the 72-hr study period, the patients’ sputum viscosity (measured using a validated qualitative sputum assessment tool) and physiological parameters will be recorded by an unblinded assessor. Total secretion volume and any HME filter changes will also be recorded, in addition to a bedside nurse satisfaction questionnaire. A median reduction in secretion viscosity of ≥ 0.5 on the qualitative sputum assessment score will be deemed as a clinically significant improvement between treatment groups. Discussion Nebulised normal saline is commonly utilised for critical care patients with high secretion loads but no randomised control trials exist to guide the technology used or frequency of administration. Novel vibrating mesh technology may also be superior to traditional jet nebulisation for nebuliser delivery. A better understanding of the changes in sputum viscosity after normal saline nebulisation will help improve secretion management during mechanical ventilation. Trial Registration https://www.clinicaltrials.gov/ct2/show/NCT05635903