Real-Time Analysis of Dry-Side Nebulization With Heated Wire Humidification During Mechanical Ventilation

BACKGROUND: Recent observational studies of nebulizers placed on the wet side of the humidifier suggest that, after some time, considerable condensation can form, which triggers an occlusion alarm. In the current study, an inline breath-enhanced jet nebulizer was tested and compared in vitro with a vibrating mesh nebulizer on the humidifier dry–inlet side of the ventilator circuit.

METHODS: Two duty cycle breathing patterns were tested during continuous infusion (5 or 10 mL/h) with and without dynamic changes in infusion flow and duty cycle, or bolus delivery (3 or 6 mL) of radiolabeled saline solution. Inhaled mass (IM) was measured by a real-time ratemeter (µCi/min) and analyzed by multiple linear regression.

RESULTS: During simple continuous infusion, IM increased linearly for both nebulizer types. IM variability was attributable to the duty cycle (P < .001) (34%) and infusion flow (P < .001) (32%) but independent of nebulizer technology (P = .38) (7%). Dynamic continuous infusion studies that simulate clinical scenarios with ventilator and pump flow changes demonstrated a linear increase in the rate of aerosol that was dependent on pump flow (P < .001) (63%) and minimally dependent on the duty cycle (P = .003) (8%). During bolus treatments, IM increased linearly to plateau. IM variability was attributable to the duty cycle (P < .001) (40%) and residual radioactivity in the nebulizer (P < .001) (20%). Separate analysis revealed that the vibrating mesh nebulizer residual volume contributed 16% of the variability and inline breath-enhanced jet nebulizer contributed 5%. IM variability was independent of bolus volume (P = .82) (1%). System losses were similar (the inline breath-enhanced jet nebulizer: 32% residual in nebulizer; the vibrating mesh nebulizer: 34% in circuitry).

CONCLUSIONS: Aerosol delivery during continuous infusion and bolus delivery was comparable between the inline breath-enhanced jet nebulizer and the vibrating mesh nebulizer, and was determined by pump flow and initial ventilator settings. Further adjustments in ventilator settings did not significantly affect drug delivery. Expiratory losses predicted by the duty cycle were reduced with placement of the nebulizer near the ventilator outlet.