In-vitro and in-vivo comparisons of high versus low concentrations of inhaled epoprostenol to adult intubated patients

Enhanced Aerosol Delivery During High-Flow Nasal Cannula Therapy

BACKGROUND

Aerosolized drug delivery via high-flow nasal cannula (HFNC) decreases as gas flow is increased. To improve aerosol delivery, breath-enhanced jet nebulizer may increase aerosol output. This study tested that hypothesis and compared breath-enhanced jet nebulizer to vibrating mesh nebulizer technology.

METHODS

First, in an isolated circuit, breath-enhanced jet nebulizer and vibrating mesh nebulizer aerosol outputs were measured during simulated HFNC by using infused saline solution at rates of 5-60 mL/h. Limits were defined when nebulizer filling was detected. The devices were then tested by using 99mTc/saline solution to measure maximum rates of aerosol production. After the output experiments, drug delivery was measured in vitro by using a model that consisted of an HFNC circuit interfaced to a realistic 3-dimensional printed head. The 99mTc/saline solution was infused at rates of 5 to 60 mL/h for the breath-enhanced jet nebulizer and 5 to 20 mL/h for the vibrating mesh nebulizer with HFNC gas flows of 10 to 60 L/min. Aerosol delivery to the trachea was measured by using a shielded ratemeter, which defined the rate of drug delivery (µg NaCl/min).

RESULTS

With increasing gas flow, breath-enhanced jet nebulizer output increased to a maximum of 50 mL/h, the vibrating mesh nebulizer maximum was 12 mL/h. At HFNC gas flow of 60 L/min, breath-enhanced jet nebulizer delivered 3.16 to 316.8 µg NaCl/min, the vibrating mesh nebulizer delivered 23.5 to 61.7 µg NaCl/min. For infusion pump flows of 5 to 12 mL/h, the rate of drug delivery was independent of nebulizer type (P = .19) and dependent on infusion pump flow (P < .001) and gas flow (P < .001).

CONCLUSIONS

Increasing gas flow increased breath-enhanced jet nebulizer output, which demonstrated the effects of breath enhancement. At 60 L/min, breath enhanced jet nebulizer delivered up to 5 times more aerosol compared with conventional vibrating mesh nebulizer technology. Breath-enhanced jet nebulizer delivered a wide range of dose rates at all high flows. In patients who are critically ill, breath-enhanced jet nebulizer technology may allow titration of bedside dosing based on clinical response by simple adjustment of the infusion rate.

In Vitro Model for Analysis of High-Flow Aerosol Delivery During Continuous Nebulization

BACKGROUND

To understand the fate of aerosols delivered by high-flow nasal cannula using continuous nebulization, an open-source anatomical model was developed and validated with a modified real-time gamma ratemeter technique. Mass balance defined circuit losses. Responsiveness to infusion rate and device technology were tested.

METHODS

A nasal airway cast derived from a computed tomography scan was converted to a 3-dimensional-printed head and face structure connected to a piston ventilator (breathing frequency 30 breaths/min, tidal volume 750 mL, duty cycle 0.50). For mass balance experiments, saline mixed with Technetium-99m was infused for 1 h. Aerosol delivery was measured using a gamma ratemeter oriented to an inhaled mass filter at the hypopharynx of the model. Background and dead-space effects were minimized. All components were imaged by scintigraphy. Continuous nebulization was tested at infusion rates of 10-40 mL/h with gas flow of 60 L/min using a breath-enhanced jet nebulizer (BEJN), and a vibrating mesh nebulizer. Drug delivery rates were defined by the slope of ratemeter counts/min (CPM/min) versus time (min).

RESULTS

The major source of aerosol loss was at the nasal interface (∼25%). Significant differences in deposition on circuit components were seen between nebulizers. The nebulizer residual was higher for BEJN (P = .006), and circuit losses, including the humidifier, were higher for vibrating mesh nebulizer (P = .006). There were no differences in delivery to the filter and head model. For 60 L/min gas flow, as infusion pump flow was increased, the rate of aerosol delivery (CPM/min) increased, for BEJN from 338 to 8,111; for vibrating mesh nebulizer, maximum delivery was 2,828.

CONCLUSIONS

The model defined sites of aerosol losses during continuous nebulization and provided a realistic in vitro system for testing aerosol delivery during continuous nebulization. Real-time analysis can quantify effects of multiple changes in variables (nebulizer technology, infusion rate, gas flow, and ventilation) during a given experiment.