What is physiological humidity?
- Under normal circumstances the upper airway functions to ensure that inhaled air reaches the lungs at body temperature (37 °C) and close to 100 % relative humidity1.
- Bypassing these warming and humidifying functions in tracheostomised patients allows cooler, dryer gases to be delivered to the carina than would normally occur.
- Within the literature, values for absolute humidity in tracheostomised patients vary between 17 and 44 mgh2O/L and tracheal temperature values range from 32 to 37 °C.2 However, the level of acceptable humidity remains the subject of some debate.3
Humidified high flow for tracheostomies?
Humidified high flow therapy has been shown to:
- Improve work of breathing (WOB) in acute care and decrease adverse clinical events in chronic care in a study of children with tracheostomies compared to a passive HME7
- Assist ventilation in a study of patients with chronic respiratory failure carrying a trans-tracheal catheter for long-term oxygen therapy compared to low-flow oxygen therapy8
- Provide higher humidification levels in a bench study compared to both active and passive HMEs, leading to the recommendation of using humidified high flow in patients who require supplemental oxygen or those with high tidal volumes9
What are the effects of sub-optimal humidity on tracheostomy patients?
- Heat and moisture loss from mucociliary epithelium, which can lead to permanent loss of ciliated epithelium4
- Reduced mucociliary clearance leading to retention of secretions5
- Drying or thickening of secretions5
- Pulmonary infection6
- Obstruction or occlusion of the airway or tracheostomy tube6
- Atelectasis2, 6