Aerosol delivery during invasive mechanical ventilation is a common practice in ICU. Optimization of drug delivery has been evaluated in many studies by comparison of static conditions.1 In this issue of Respiratory Care, Lee et al reported a series of experiments involving the use of a breath-enhanced jet nebulizer placed on the dry side of the humidifier in a model of an adult receiving invasive respiratory support.2 The same group had previously reported another series of studies using the same nebulizer but placing it on the wet side of the humidifier.3 The authors realized after a more prolonged observation of the technology that placement of the nebulizer affected function of the ventilator. The investigators used radio-labeled aerosols to provide real-time delivery data using a newly developed technique.4 Lee et al2 compared a vibrating mesh nebulizer and a breath-enhanced nebulizer in 3 commonly used ventilator brands with 2 different breathing patterns. They studied continuous nebulization under steady and variable breathing patterns and during bolus therapy using 2 different volumes.
The authors first evaluated inhaled and exhaled mass during continuous nebulization over a 90-min period. They found that breathing patterns with prolonged expiratory time resulted in similar expiratory masses irrespective of the pump flow. They also reported that increased duty cycle and higher pump flow resulted in higher inhaled mass (see Table 2 in the article). In a multiple linear regression analysis, the authors found that neither nebulizer type nor nebulizer residual contributed to the variability seen in inhaled mass (see Table 3 in the article). Continuous operation was also evaluated through dynamic changes occurring over 220 min. Lee et al2 mitigated the known disadvantage of repeated measures design (ie, order effects) by changing the order in which the continuous experiments were done (see Table 4 in the article). In a multiple linear regression analysis, the authors found that pump flow was the main independent variable responsible for the variability seen in inhaled mass. Lee et al2 found a linear increased in inhaled mass over time for the 90- and 220-min setups.
Bolus aerosol delivery was evaluated using 2 different loading volumes (3 and 6 mL). The authors reported an increase of inhaled mass of 37% and 13% for the breathing patterns with high and low duty cycles, respectively, when bolus volume was increased in the breath-enhanced nebulizer. As previously reported, inhaled mass was unchanged for vibrating mesh nebulizer with breathing pattern with low duty cycle. However, a 24% decline in inhaled mass was reported when bolus volume was increased in the same type of nebulizer while used in a model with high duty cycle (see Table 6 in the article). The explanation for this is unclear, and finding should be replicated before changes in practice are made. In a multiple linear regression analysis, the authors found that duty cycle and nebulizer residual, but neither bolus volume nor nebulizer type, contributed to the variability seen in inhaled mass.
The authors reported mass balance data for both nebulizers. They found similar overall losses with different distributions. As expected, nebulizer residual was lower and expiratory mass was higher in the vibrating mesh than in the breath-enhanced device.
The study has limitations that are inherent to its in vitro nature. One limitation is that the investigators used a passive lung model without adjustments for compliance or resistance. Another limitation is that they restricted their study by design to an adult model of mechanical ventilation. Finally, this study, like most others, used only one solution of certain physicochemical characteristics. Therefore, findings of this study should not be extrapolated to either pediatric/neonatal population or drugs of different physicochemical characteristics.
In summary, the investigators reported similar performance of a breath-enhanced and vibrating mesh nebulizer during bolus and continuous nebulization in a model of adult mechanical ventilation. The respiratory care community looks forward to more options that are efficient, less expensive, and applicable to different populations.5
This study reminds us that continuous monitoring of new and old technologies is required to ensure patient safety. It is also important to remember that findings of any study should be independently replicated before becoming mainstream.
Footnotes
- Correspondence: Ariel Berlinski MD FAARC, 1 Children’s Way, Slot 512–17, Little Rock, AR 72202. E-mail: berlinskiariel{at}uams.edu
See the Original Study on Page 914
Dr Berlinski discloses relationships with the Cystic Fibrosis Foundation, Therapeutic Development Network, National Institutes of Health, Mylan, Vertex, Trudell Medical International, and the International Pharmaceutical Aerosol Consortium on Regulation and Science.
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