Published in:
01-09-2011 | Original Article
Effect of tubing condensate on non-invasive positive pressure ventilators tested under simulated clinical conditions
Published in: Sleep and Breathing | Issue 3/2011
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Rationale
Water condensate in the humidifier tubing can affect bi-level ventilation by narrowing tube diameter and increasing airflow resistance. We investigated room temperature and tubing type as ways to reduce condensate and its effect on bi-level triggering and pressure delivery. In this bench study, the aim was to test the hypothesis that a relationship exists between room temperature and tubing condensate.
Methods
Using a patient simulator, a Res-med bi-level device was set to 18/8 cm H2O and run for 6 h at room temperatures of 16°C, 18°C and 20°C. The built-in humidifier was set to a low, medium or high setting while using unheated or insulated tubing or replaced with a humidifier using heated tubing. Humidifier output, condensate, mask pressure and triggering delay of the bi-level were measured at 1 and 6 h using an infrared hygrometer, metric weights, Honeywell pressure transducer and TSI pneumotach.
Results
When humidity output exceeded 17.5 mg H2O/L, inspiratory pressure fell by 2–15 cm H2O and triggering was delayed by 0.2–0.9 s. Heating the tubing avoided any such ventilatory effect whereas warmer room temperatures or insulating the tubing were of marginal benefit.
Conclusions
Users of bi-level ventilators need to be aware of this problem and its solution. Bi-level humidifier tubing may need to be heated to ensure correct humidification, pressure delivery and triggering.