Resistive pressure of a condenser humidifier in mechanically ventilated patients.
OBJECTIVE
Heat and moisture exchangers (or "nose" humidifiers) are commonly used to aid in the humidification of inspired gases of mechanically ventilated patients. These devices add resistance to the ventilator circuit that has heretofore not been quantified in critically ill patients. Accordingly, we determined the resistive pressures associated with new and old (but < 24 hrs in the circuit) humidifiers in 23 critically ill, mechanically ventilated patients.


METHODS
Prospective study.


METHODS
Adult medical and surgical intensive care units at a university center.


METHODS
Twenty-three critically ill, mechanically ventilated patients using a condenser humidifier between the wye and the endotracheal tube.


METHODS
Peak and plateau airway pressures were determined with the humidifier in place. These measurements were repeated without the humidifier, then after insertion of a fresh humidifier into the circuit. In five patients, measurements were repeated after humidifiers had remained in place for a full 24 hrs.


RESULTS
The new humidifiers increased the resistive pressure of the ventilator circuit by 4.8 +/- 2.6 cm H2O compared with no humidifier (p < .01) and had a mean resistance of 4.2 +/- 1.5 cm H2O/L/sec. Old humidifiers increased resistive pressure by 6.3 +/- 3.6 cm H2O compared with no humidifier (p < .01) and had a mean resistance of 5.1 +/- 1.8 cm H2O/L/sec. The resistive pressure doubled from 3.4 +/- 1.2 to 7.0 +/- 1.8 cm H2O (p < .01) in five patients in whom the humidifiers were left in the ventilator circuit for a full 24 hrs.


CONCLUSIONS
The humidifier adds a significant resistance to the ventilator circuit which may lead to incorrect assessment of respiratory system mechanics, to inappropriate therapy (e.g., bronchodilators), or to difficulty in weaning from mechanical ventilation.
Department of Medicine, University of Chicago, IL.
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Manthous
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Schmidt
D000328:Adult; D000368:Aged; D000403:Airway Resistance; D003422:Critical Care / Q000706:statistics & numerical data; D006801:Humans; D006813:Humidity; D008875:Middle Aged; D011312:Pressure; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000295:instrumentation* / Q000706:statistics & numerical data; D013997:Time Factors; D012122:Ventilators, Mechanical / Q000706:statistics & numerical data