Multidrug Aerosol Delivery During Mechanical Ventilation

Background: In the critically ill, pulmonary vasodilators are often provided off label to intubated patients using continuous nebulization. If additional aerosol therapies such as bronchodilators or antibiotics are needed, vasodilator therapy may be interrupted. This study assesses aerosol systems designed for simultaneous delivery of two aerosols using continuous nebulization and bolus injection without interruption or circuit disconnection. Methods: One i-AIRE dual-port breath-enhanced jet nebulizer (BEJN) or two Aerogen® Solo vibrating mesh nebulizers (VMNs) were installed on the dry side of the humidifier. VMN were stacked; one for infusion and the second for bolus drug delivery. The BEJN was powered by air at 3.5 L/min, 50 psig. Radiolabeled saline was infused at 5 and 10 mL/h with radiolabeled 3 and 6 mL bolus injections at 30 and 120 minutes, respectively. Two adult breathing patterns (duty cycle 0.13 and 0.34) were tested with an infusion time of 4 hours. Inhaled mass (IM) expressed as % of initial syringe activity (IM%/min) was monitored in real time with a ratemeter. All delivered radioaerosol was collected on a filter at the airway opening. Transients in aerosol delivery were measured by calibrated ratemeter. Results: IM%/h during continuous infusion was linear and predictable, mean ± standard deviation (SD): 2.12 ± 1.45%/h, 2.47 ± 0.863%/h for BEJN and VMN, respectively. BEJN functioned without incident. VMN continuous aerosol delivery stopped spontaneously in 3 of 8 runs (38%); bolus delivery stopped spontaneously in 3 of 16 runs (19%). Tapping restarted VMN function during continuous and bolus delivery runs. Bolus delivery IM% (mean ± SD): 20.90% ± 7.01%, 30.40% ± 11.10% for BEJN and VMN, respectively. Conclusion: Simultaneous continuous and bolus nebulization without circuit disconnection is possible for both jet and mesh technology. Monitoring of VMN devices may be necessary in case of spontaneous interruption of nebulization.

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.

Real-Time In Vitro Assessment of Aerosol Delivery During Mechanical Ventilation

Background: A new real-time method for assessing factors determining aerosol delivery is described.

Methods: A breath-enhanced jet nebulizer operated in a ventilator/heated humidifier system was tested during bolus and continuous infusion aerosol delivery. ^99mTc (technetium)/saline was either injected (3 or 6 mL) or infused over time into the nebulizer. A shielded gamma ratemeter was oriented to count radioaerosol accumulating on an inhaled mass (IM) filter at the airway opening of a test lung. Radioactivity measured at 2–10-minute intervals was expressed as % nebulizer charge (bolus) or % syringe activity per minute infused. All circuit parts were measured and imaged by gamma camera to determine mass balance.

Results: Ratemeter activity quantitatively reflected immediate changes in IM: 3 and 6 mL bolus IM% = 16.1 and 18.8% in 6 and 14 minutes, respectively; infusion IM% = 0.64 + 0.13 (run time, min), R² 0.999. Effect of nebulizer priming and system anomalies were readily detected in real time. Mass balance (basis = dose infused in 90 minutes): IM 39.2%, breath-enhanced jet nebulizer residual 35.5%, circuit parts including humidifier 23.4%, and total recovery 98.1%. Visual analysis of circuit component images identified sites of increased deposition.

Conclusion: Real-time ratemeter measurement with gamma camera imaging provides operational feedback during in vitro testing procedures and yields a detailed analysis of the parameters influencing drug delivery during mechanical ventilation. This method of analysis facilitates assessment of device function and influence of circuit parameters on drug delivery.

Factors Determining Continuous Infusion Aerosol Delivery During Mechanical Ventilation

BACKGROUND

Continuous nebulization of prostacyclins and albuterol by infusion pump during mechanical ventilation evolved as a popular off-label treatment for severe hypoxemic respiratory failure and asthma. Most institutions use a vibrating mesh nebulizer. A new breath-enhanced jet nebulizer is a potential alternative. This study was designed to compare these devices to better define factors influencing continuous infusion aerosol delivery. Device function, ventilator settings, and infusion pump flow were studied in vitro.

METHODS

Using a bench model of adult mechanical ventilation, radiolabeled saline was infused at 6 flows (1.5-12 mL/h) into test nebulizers; 4 examples of each were used in rotation to test device reproducibility. Four breathing patterns with duty cycles (percentage of inspiratory time) ranging from 0.13 to 0.34 were tested. The vibrating mesh nebulizer was installed on the "dry" side of the heated humidifier (37°C). The breath-enhanced jet nebulizer, installed on the "wet" side, was powered by air at 3.5 L/min and 50 psi. Infusion time was 1 h. Inhaled mass of aerosol was collected on a filter at the airway opening. Inhaled mass was expressed as the percentage of the initial syringe radioactivity delivered per hour. Radioactivity deposited in the circuit was measured with a gamma camera. Data were analyzed with multiple linear regression.

RESULTS

Variation in inhaled mass was significantly explained by pump flow and duty cycle (R² 0.92) and not by nebulizer technology. Duty cycle effects were more apparent at higher pump flow. Vibrating mesh nebulizers failed to nebulize completely in 20% of the test runs. Mass balance indicated that vibrating mesh nebulizers deposited 15.3% in the humidifier versus 0.2% for breath-enhanced jet nebulizer.

CONCLUSIONS

Aerosol delivery was determined by infusion pump flow and ventilator settings with comparable aerosol delivery between devices. The breath-enhanced jet nebulizer was more reliable than the vibrating mesh nebulizer; 10-12 mL/h was the maximum infusion flow for both nebulizer technologies.

Face Mask Leak Determines Aerosol Delivery in Noninvasive Ventilation

BACKGROUND

Aerosol transport during noninvasive ventilation follows the flow of pressurized gas through the noninvasive ventilation circuit, vented via leak port and face mask, and inhaled by the patient. Recommendations for nebulizer placement are based on in vitro models that have focused primarily on aerosol losses via the leak port; face mask leaks have been avoided. This study tested aerosol delivery in the setting of controlled face mask leak.

METHODS

Three nebulizer technologies were studied on a bench model using a lung simulator with a face mask placed onto a manikin head. Radiolabeled aerosol delivery (ie, inhaled mass) was determined by mass balance using filters and a gamma camera that tested the effects of nebulizer location and face mask leak. Low (15-20 L/min) and high (55-60 L/min) mask leaks were used to mimic realistic clinical conditions.

RESULTS

Inhaled mass (% nebulizer charge) was a function of nebulizer technology (with the nebulizer at ventilator outlet position: Aerogen 22.8%, InspiRx 11.1%, and Hudson 8.1%; P = .001). The location of the nebulizer before or after the leak port was not important (P = 0.13 at low leak and P = 0.38 at high leak). Aerosol delivery was minimal with high mask leak (inhaled mass 1.5-7.0%). Aerosol losses at the leak port at low mask leak were 28-36% versus 9-24% at high mask leak. Aerosol losses via the mask leak were 16-20% at low mask leak versus 46-72% at high mask leak. Furthermore, high face mask leak led to significant deposition on the mask and face (eg, up to 50% of the nebulizer charge with the Aerogen mask).

CONCLUSIONS

During noninvasive ventilation, nebulizer placement at the ventilator outlet, which is a more practical position, is effective and minimizes deposition on face and mask. Aerosol therapy should be avoided when there is high face mask leak.

Comparison of Vibrating Mesh, Jet, and Breath-Enhanced Nebulizers During Mechanical Ventilation

BACKGROUND

This study compared 3 nebulizer technologies for inter- and intradevice reproducibility, humidification, and fill volume sensitivity during mechanical ventilation: a breath-enhanced jet nebulizer, a vibrating mesh nebulizer, and a jet nebulizer. The breath-enhanced jet nebulizer featured a new design located on the wet side of the humidifier to reduce aerosol loss and potential humidifier contamination. The vibrating mesh nebulizer and the jet nebulizer were placed on the dry side.

METHODS

Aerosol delivery was measured using multiple ventilator settings (inspiratory time = 0.45-1.01 s). Using radiolabeled saline and a gamma camera, bench studies were performed using a ventilator to test 4 breathing patterns. Four scenarios were assessed during testing: 3 mL and 6 mL fill volumes with and without heated wire humidification. Measurements included inhaled mass (as a percentage of the nebulizer charge), nebulizer residual, mass balance, and aerosol particle size distribution. Statistics were determined using Mann-Whitney and linear regression.

RESULTS

The inhaled mass for the breath-enhanced jet nebulizer was 10.5-29.2% and was affected by fill volume (P = .004) but not by humidity. The inhaled mass for the vibrating mesh nebulizer was 0.9-33% and was unaffected by fill volume and humidity. The inhaled mass for the jet nebulizer was 2.5-25.9% and was affected by both fill volume (P = .009) and humidity (3 mL, P = .002). The inhaled mass for the vibrating mesh nebulizer was more variable due to random failures to achieve complete nebulization, and inhaled mass correlated closely with residual mass: IM% = -0.233(Residual%) + 24.3, r² = 0.67, P < .001. For all devices, large particles were lost in the ventilator tubing; large particles were also lost in the humidifier for the vibrating mesh nebulizer (17% nebulizer charge), resulting in similar particle distributions (mass median aerodynamic diameter 1.33-1.95 μm) for all devices.

CONCLUSIONS

Nebulization with the breath-enhanced jet nebulizer was less sensitive to humidification than the jet nebulizer. Delivery via the vibrating mesh nebulizer was not predictable, with random failure to empty (55% experimental runs). All devices delivered similar particle distributions. Wet-side aerosol delivery avoids humidifier contamination, and breath-enhanced technology can ensure better control of drug delivery.

Reliability of Vibrating Mesh Technology

BACKGROUND

For delivery of inhaled aerosols, vibrating mesh systems are more efficient than jet nebulizers are and do not require added gas flow. We assessed the reliability of a vibrating mesh nebulizer (Aerogen Solo, Aerogen Ltd, Galway Ireland) suitable for use in mechanical ventilation.

METHODS

An initial observational study was performed with 6 nebulizers to determine run time and efficiency using normal saline and distilled water. Nebulizers were run until cessation of aerosol production was noted, with residual volume and run time recorded. Three controllers were used to assess the impact of the controller on nebulizer function. Following the observational study, a more detailed experimental protocol was performed using 20 nebulizers. For this analysis, 2 controllers were used, and time to cessation of aerosol production was noted. Gravimetric techniques were used to measure residual volume. Total nebulization time and residual volume were recorded. Failure was defined as premature cessation of aerosol production represented by residual volume of > 10% of the nebulizer charge.

RESULTS

In the initial observational protocol, an unexpected sporadic failure rate was noted of 25% in 55 experimental runs. In the experimental protocol, a failure rate was noted of 30% in 40 experimental runs. Failed runs in the experimental protocol exhibited a wide range of retained volume averaging ± SD 36 ± 21.3% compared with 3.2 ± 1.5% (P = .001) in successful runs. Small but significant differences existed in nebulization time between controllers.

CONCLUSIONS

Aerogen Solo nebulization was often randomly interrupted with a wide range of retained volumes.

In vitro delivery of aerosolized treprostinil via modern mechanical ventilation

BACKGROUND

The Tyvaso Inhalation System is a hand-held nebulizer system used to administer treprostinil, an approved therapy for pulmonary arterial hypertension. Our goal was to establish an in vitro method for delivering a standard dose of treprostinil through a ventilator circuit and artificial airway.

METHODS

An AeroTech II jet nebulizer (continuous air flow at 10 L/min; Biodex Medical Systems) was placed in the ventilator circuit with a test lung. Two ventilators were tested, the Dräger Evita 2 Dura (Dräger Medical GmbH) and Avea (CareFusion), without humidity. Delivered dose was defined by capturing radiolabeled particles exiting the endotracheal tube with a filter (Pari) and measuring radioactivity. Particle distributions were measured distal to the endotracheal tube by cascade impaction. We hypothesized that drug delivery would be determined by the number of breaths needed, such that the complete time of inspiration totaled 29 sec (e.g., number of breaths needed=29 sec/TI, where TI is the inspiratory time of an average breath read from the ventilator display).

RESULTS

Nebulizer output was linear for 6 min, and the standard prescribed target dose of 54 μg (3.1% of full ampule) was delivered in 29 sec. Using our TI algorithm to control delivery, the mean inhaled dose±SD was 72.2±16.5 μg (range 47.2-98.6; n=23). Dräger delivered higher doses than Avea. Effects of mode, breathing pattern, and positive-end expiratory pressures were not significant. The mass median aerodynamic diameter and fine particle fraction were 0.71±0.015 and 0.997±0.0006, respectively.

CONCLUSIONS

Using the algorithm, it was possible to deliver aerosolized treprostinil, at controlled doses, via mechanical ventilation over a wide range of controlled breathing patterns. The conditions of nebulization must be precisely followed (one full ampule per treatment, use of the AeroTech II nebulizer, continuous nebulization using an external flow of 10 L/min, bypass of the humidifier or removal of in-line heat and moisture exchanger, and treatment completed in 6 min or less).