Effects of dense, high-volume, artificial surfactant aerosol on a heated exhalation filter system

C F Haas, J G Weg, C W Kettell, E J Caldwell, D S Zaccardelli, D L Brown
Critical Care Medicine 1993, 21 (1): 125-30

OBJECTIVE: To evaluate a supplemental heated filter system during mechanical ventilation with continuous nebulization of an artificial surfactant by a new, high-volume nebulizer.

DESIGN AND METHODS: A new nebulizer system, containing artificial surfactant, provided half of a 20-L minute ventilation and the remainder of this minute ventilation was provided by a commonly used mechanical ventilator. Ventilation sources were joined in the inspiratory limb of the breathing circuit, which was connected to a test lung system. A supplemental filter system was placed upstream of the ventilator's heated filter in the expiratory limb of the circuit. Circuit pressures at the inlet of the supplemental filter (P1), between the filters (P2), and after the ventilator expiratory filter (P3) were monitored and recorded. Nebulizer canisters containing artificial surfactant were replaced every 4 hrs. The performance of four supplemental filters in continuous use was examined. Another four filters were each used over 4 hrs, steam autoclaved, and reused.

SETTINGS: The ventilator was set at a rate of 20 breaths/min, with a tidal volume of 0.5 L, a flow rate of 40 L/min, and positive end-expiratory pressure of 10 cm H2O. The nebulizer provided an equal volume and flow rate so that the delivered tidal volume was 1.0 L with a flow rate of 80 L/min.

RESULTS: Ventilator failure and/or excessive airway pressure caused by increased filter resistance occurred at a mean of 7.3 +/- 1.3 (SD) hrs of continuous ventilation. Mean P1-peak increased from 67.5 +/- 8.2 to 94.0 +/- 10.7 cm H2O (p < .001) and P1-baseline increased from 9.3 +/- 1.0 to 53.5 +/- 17.1 cm H2O (p = .014). Filters that were autoclaved after 4 hrs of ventilation and reused lasted a total of 7.0 +/- 1.3 hrs. Mean P1-peak increased from 68.9 +/- 4.9 to 84.8 +/- 19.1 cm H2O and P1-baseline increased from 9.5 +/- 1.7 to 30.8 +/- 14.2 cm H2O (p < .05).

CONCLUSIONS: The supplemental filter system was able to protect the ventilatory exhalation sensors for approximately 7 hrs at a minute ventilation of 20 L/min. Steam sterilization did not extend the supplemental filter life.

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