Effect of tubing condensate on non-invasive positive pressure ventilators tested under simulated clinical conditions

Hart, Diana; Forman, Mark; Veale, Andrew
September 2011
Sleep & Breathing;Sep2011, Vol. 15 Issue 3, p535
Academic Journal
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 HO 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 HO/L, inspiratory pressure fell by 2-15 cm HO 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.


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