Abstract
Background:
Aerosol drug delivery by devices positioned on the “wet” side of the humidifier is significantly affected by humidification, with reported aerosol losses of 50 to 75% for nebulizers and 40% for MDIs. The unpredictable losses in these circuits led some investigators to advocate avoidance of active humidification during aerosol therapy. However, humidification is required for prolonged delivery of controlled doses of drugs (eg, vasodilators). Recently, we tested wet-side nebulization using a prototype breath-enhanced nebulizer and achieved good control of drug delivery. However, short term aerosol studies do not assess the stability of ventilator circuit humidification over time when devices are left in the circuit. To test this stability, we studied the humidified ventilator circuit over 24-48 hours using wet-side nebulizer placement on the humidifier.
Methods:
A standard F&P humidifier/heated wire circuit was operated continuously during mechanical ventilation of test lungs over several days with a prototype i-AIRE breath-enhanced nebulizer or Aerogen Solo positioned at the humidifier outlet. The humidifier outlet thermistor was located either at the inlet cuff of the inspiratory limb or the humidifier outlet. Room temperature was controlled at 22 C. Periodically, the devices and inspiratory limb tubing were assessed for water accumulation, and the ventilator for alarm conditions.
Results:
Within 24-48 h, enough condensation formed within all devices and/or the inspiratory limb to trigger an occlusion alarm on the ventilator. By applying insulating materials, condensation was shown to be a function of heat loss caused by interposing devices between the humidifier outlet and the inspiratory limb (where the heated wire begins). This phenomenon could not be avoided by moving the thermistor to different locations.
Conclusions:
Positioning nebulizing devices on the wet side of the humidifier with a heated wire circuit is not feasible. Nebulizing systems left in the circuit should be located on the dry side of the humidifier.
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