Pump Infusion Rate During Continuous Nebulization in a Mechanically Ventilated Pediatric Bench Model Affects the Percentage of Active Nebulization Time

Background:

Manufacturer guidelines for the vibrating mesh nebulizer (VMN) recommends a maximum pump infusion rate of 12ml/h during continuous aerosolization, but in following this guideline there may be instances when drug delivery is not optimal due to gaps in active nebulization during mechanical ventilation. Increasing the pump infusion rate could be considered in order to minimize periods of inactive nebulization time. The purpose of this experiment was to observe the effect of increasing the continuous nebulizer pump infusion rate and its impact on the percentage of active and inactive nebulization time during mechanical ventilation with high ventilation pressures.

Methods:

AVEA and Servo-I ventilators were calibrated and placed in pressure control mode (Rate 10, PIP 32, PEEP 12, PS 10, 1.0 i-time, 50% FIO₂) and set to ventilate a passive test lung. An Alaris Pump with a 60 mL syringe was filled with normal saline, primed, and connected to a vibrating mesh nebulizer (Aerogen). The nebulizer was placed on the dry side of the humidifier, and left nebulizing in continuous mode. The infusion rate on the pump was tested on 18, 20, and 22mL/h for a period of 10 min per run and a stopwatch was used to record the time the nebulizer spent nebulizing in each 10 min period on each flow. We computed the percentage of time the nebulizer was actively nebulizing a visible plume in the 10 min period. Each test was repeated three times with three different nebulizers.

Results:

The mean percentage of time for active nebulization is shown in the Figure for each ventilator. The AVEA ventilator had a lower average percentage of time in active nebulization in a 10-min period and higher standard deviation than the Servo-i (78 ± 12%, and 94 ± 2% respectively). When using the highest input flows of 22ml/h, there were runs where the output of the nebulizer exceeded the input of the pump resulting in percentage of time nebulizing < 100%.

Conclusions:

The percentage of time a VMN spends actively nebulizing is affected by the pump infusion flow chosen and the ventilator used. When using high ventilator pressures, an infusion rate greater than the manufacturer guidelines can still result in significantly low percentage of time nebulizing. Care should be taken to titrate infusion rates when necessary while acknowledging the potential for differences in nebulization rate between devices and when used in a different make of ventilator.

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