Effect of tubing condensate on non-invasive positive pressure ventilators tested under simulated clinical conditions.
BACKGROUND
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 H(2)O 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 H(2)O/L, inspiratory pressure fell by 2-15 cm H(2)O 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.
Hart
Diana Elizabeth
DE
Department of Respiratory Medicine, Middlemore Hospital, Auckland, New Zealand. dehart@middlemore.co.nz
Forman
Mark
M
Veale
Andrew G
AG
D000399:Air Pressure; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation*; D019544:Equipment Failure Analysis; D006361:Heating; D006801:Humans; D006813:Humidity; D008953:Models, Anatomic; D012123:Pulmonary Ventilation; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D013223:Statistics as Topic; D014160:Transducers, Pressure