Microbiome-scale analysis of aerosol facemask contamination during nebulization therapy in hospital.

BACKGROUND: Microbial contamination of aerosol facemasks could be a source of nosocomial infections during nebulization therapy in hospital, prompting efforts to identify these contaminants. Identification of micro-organisms in medical devices has traditionally relied on culture-dependent methods, which are incapable of detecting the majority of these microbial contaminants. This challenge could be overcome with culture-independent sequencing-based techniques that are suited for the profiling of complex microbiomes. AIM: To characterize the microbial contaminants in aerosol facemasks used for nebulization therapy, and identify factors influencing the composition of these microbial contaminants with the acquisition and analysis of comprehensive microbiome-scale profiles using culture-independent high-throughput sequencing. METHODS: Used aerosol facemasks collected from hospitalized patients were analysed with culture-independent 16S rRNA gene-based amplicon sequencing to acquire microbiome-scale comprehensive profiles of the microbial contaminants. Microbiome-based analysis was performed to identify potential sources of microbial contamination in facemasks. FINDINGS: Culture-independent high-throughput sequencing was demonstrated for the capacity to acquire microbiome-scale profiles of microbial contaminants on aerosol facemasks. Microbial source identification enabled by the microbiome-scale profiles linked microbial contamination on aerosol facemasks to the human skin and oral microbiota. Antibiotic treatment with levofloxacin was found to reduce contamination of the facemasks by oral microbiota. CONCLUSION: Sequencing-based microbiome-scale analysis is capable of providing comprehensive characterization of microbial contamination in aerosol facemasks. Insight gained from microbiome-scale analysis facilitates the development of effective strategies for the prevention and mitigation of the risk of nosocomial infections arising from exposure to microbial contamination of aerosol facemasks, such as targeted elimination of potential sources of contamination.

Microbiome-based source identification of microbial contamination in nebulizers used by inpatients.

Nebulizers are essential for the delivery of aerosolized medication for respiratory patients in hospital. Microbial contamination of nebulizers increases the risk of healthcare-associated infections, presenting the critical need to identify sources of contamination in order to develop effective infection prevention and control practices in hospitals. Using an innovative microbiome-based cultivation-independent microbial source identification technique, the hospital indoor environment was identified as a significant source contributing to microbial contaminants in nebulizers, providing important information to develop strategies for targeted decontamination and enhance the effectiveness of infection prevention and control practices.

What the pulmonary specialist should know about the new inhalation therapies.

A collaboration of multidisciplinary experts on the delivery of pharmaceutical aerosols was facilitated by the European Respiratory Society (ERS) and the International Society for Aerosols in Medicine (ISAM), in order to draw up a consensus statement with clear, up-to-date recommendations that enable the pulmonary physician to choose the type of aerosol delivery device that is most suitable for their patient. The focus of the consensus statement is the patient-use aspect of the aerosol delivery devices that are currently available. The subject was divided into different topics, which were in turn assigned to at least two experts. The authors searched the literature according to their own strategies, with no central literature review being performed. To achieve consensus, draft reports and recommendations were reviewed and voted on by the entire panel. Specific recommendations for use of the devices can be found throughout the statement. Healthcare providers should ensure that their patients can and will use these devices correctly. This requires that the clinician: is aware of the devices that are currently available to deliver the prescribed drugs; knows the various techniques that are appropriate for each device; is able to evaluate the patient's inhalation technique to be sure they are using the devices properly; and ensures that the inhalation method is appropriate for each patient.

Advanced nebulizer designs employing vibrating mesh/aperture plate technologies for aerosol generation.

Recent technological advances and improved nebulizer designs have overcome many limitations of jet nebulizers. Newer devices employ a vibrating mesh or aperture plate (VM/AP) for the generation of therapeutic aerosols with consistent, increased efficiency, predominant aerosol fine particle fractions, low residuals, and the ability to nebulize even microliter volumes. These enhancements are achieved through several different design features and include improvements that promote patient compliance, such as compact design, portability, shorter treatment durations, and quiet operation. Current VM/AP devices in clinical use are the Omron MicroAir, the Nektar Aeroneb, and the Pari eFlow. However, some devices are only approved for use with specific medications. Development of "smart nebulizers" such as the Respironics I-neb couple VM technologies with coordinated delivery and optimized inhalation patterns to enhance inhaled drug delivery of specialized, expensive formulations. Ongoing development of advanced aerosol technologies should improve clinical outcomes and continue to expand therapeutic options as newer inhaled drugs become available.

Comparative analysis of methods to measure aerosols generated by a vibrating mesh nebulizer.

Different approaches have been employed for in vitro assessment of the aerosol particle size generated by inhalation devices. In this study, aerosols from the Omron MicroAir vibrating mesh (VM) nebulizer were measured by cascade impaction (CI) using the MSP Next Generation Pharmaceutical Impactor (NGI), the ThermoAndersen Cascade Impactor (ACI), and by time-of-flight (TOF) analysis with the TSI 3321 Aerodynamic Particle Sizer Spectrometer (APS). The VM nebulizer was evaluated with sodium fluoride (NaF; 2.5%) and with generic albuterol (0.083%). Aerosol particle size (MMAD), respirable fractions (RF < 5 microm), and fine particle fractions (FPF < 3.3 microm) were determined with each method at room temperature (RT) and 4 degrees C using 50% average relative humidity. By NGI at either RT or 4 degrees C, aerosol particle sizes were similar for both NaF and albuterol (4.3-4.5 microm MMAD) with 55-61% RF and 27-43% FPF. With ACI, the distribution of particles at RT was similar except at the extremes of the dispersion and the MMAD was smaller (3.3 microm MMAD; p = 0.03). At 4 degrees C, particle sizes determined by ACI results were similar to the NGI (MMAD 4.1 microm; p > 0.05). TOF analysis by APS with albuterol gave significantly larger calculated MMAD (cMMAD) than either CI method (7.2 microm; p < 0.001). TOF measurements of nebulized albuterol at RT and 4 degrees C were equivalent. In summary, the results of VM nebulized NaF and albuterol were more consistent and generally equivalent when determined by NGI (at RT and 4 degrees C) and ACI analysis (at 4 degrees C). In contrast, aerosol particle sizes measured by TOF in the APS at both RT and 4 degrees C were larger than results obtained by CI. Differences in aerosol particle distribution obtained by different analysis methods should be considered while evaluating the in vitro performance of VM nebulizers.

Selecting an accessory device with a metered-dose inhaler: variable influence of accessory devices on fine particle dose, throat deposition, and drug delivery with asynchronous actuation from a metered-dose inhaler.

Accessory devices reduce common problems with metered-dose inhalers (MDIs), namely high oropharyngeal deposition of aerosol and incoordination between actuation and inhalation by the patient. The objective of this study was to systematically compare the performance of various accessory devices in vitro. MDIs were tested alone or in combination with four spacers (Toilet paper roll, Ellipse, Optihaler, Myst Assist) and five holding chambers (Aerochamber, Optichamber, Aerosol Cloud Enhancer, Medispacer, and Inspirease). An Anderson cascade impactor was used to measure aerosol mass median aerodynamic diameter (MMAD) and fine particle dose (MMAD < 4.7 microm). In separate experiments, the influence of asynchronous MDI actuation on drug delivery was determined with a simulated spontaneous breathing model. Compared with the MDI alone, all of the accessory devices reduced aerosol MMAD and increased lung-throat ratio (fine particle dose/throat impaction; p < 0.05 for both parameters). The fine particle dose of albuterol was 40% higher with the Ellipse (p < 0.01), was equivalent with the Toilet Paper Roll, Aerochamber, Optichamber, and Medispacer, and was 33-56% lower with the Optihaler, Myst Assist, Aerosol Cloud Enhancer, and Inspirease (p < 0.03). MDI actuation in synchrony with inspiration produced highest drug delivery; when MDI actuation occurred 1-sec before inspiration or during exhalation, decrease in drug delivery with holding chambers (10-40% reduction) was less than that with spacers (40-90% reduction). Accessory device selection is complicated by variability in performance between devices, and in the performance of each device in different clinical settings. In vitro characterization of a MDI and accessory device could guide appropriate device selection in various clinical settings.

Inhalation therapy during mechanical ventilation.

An increasing number of pharmacologic agents, including bronchodilators, prostaglandin, proteins, surfactant, mucolytics, and antibiotics are administered to mechanically ventilated patients by the inhalation route. To achieve a therapeutic effect, adequate amounts of an inhaled agent must be delivered to the desired site of action. The delivery of inhaled drugs to the lower respiratory tract of mechanically ventilated patients is complicated by deposition of the aerosol particles in the ventilator circuit and endotracheal tube, and the factors governing pulmonary deposition in mechanically ventilated patients are different from those in ambulatory patients. Meticulous adherence to several steps in the technique of aerosol administration is necessary for successful aerosol therapy in mechanically ventilated patients. With a proper technique of administration, an increasing number of inhaled drugs may be administered safely, conveniently, and effectively to mechanically ventilated patients.

Laboratory evaluation of metered-dose inhalers with models that simulate interaction with the patient.

Laboratory evaluation of aerosol generating-devices is usually performed under conditions of constant airflow. The performance of aerosol-generating devices with different tidal volumes and inspiratory airflows encountered in clinical practice cannot be determined by these methods. To overcome this problem, models have been developed that simulate patients' breathing pattern, provide measurements of inhaled or respirable mass, and the proportion of aerosol exhaled. This article explores the development of such a model.

Future directions in aerosol therapy.

An unprecedented growth in new technology and clinical applications of aerosol therapy is forecast for the new millennium. The most promising areas of investigation in the aerosol field relate to improvements in the pulmonary deposition of aerosol, improved synchronization between the patient's breathing and aerosol generation, targeting of aerosol to specific sites in the lung, improvements in the formulations of inhaled drugs, modulated release of inhaled drugs, and use of inhaled drugs for systemic therapy. Moreover, gene therapy by the inhaled route offers the prospects of a cure for a variety of pulmonary disorders. Future developments in the aerosol field are expected to radically change the management of patients across several medical specialties.

Improvement in aerosol delivery with helium-oxygen mixtures during mechanical ventilation.

In mechanically ventilated patients with airway obstruction, helium-oxygen (He-O2) mixtures reduce airway resistance and improve ventilation, but their influence on aerosol delivery is unknown. Accordingly, we determined the effect of various He-O2 mixtures on albuterol delivery from metered-dose inhalers (MDIs) and jet nebulizers in an in vitro model of mechanical ventilation. Albuterol delivery from a MDI was increased when the ventilator circuit contained 80% helium and 20% oxygen (He-O2 80/20) versus O2: 46.7 +/- 3.3 versus 30.2 +/- 1.3 (SE)% of the nominal dose (p < 0.001)-the difference was mainly due to decreased drug deposition in the spacer chamber, mean 39.2% and 55.2%, respectively (p < 0.001). Nebulizer efficiency at a flow rate of 6 L/min was five times lower with He-O2 80/20 than O2, and the amount of nebulized drug was inversely correlated with gas density (r = 0.94, p < 0.0001). When the nebulizer was operated with O2, greater albuterol delivery was achieved when the ventilator circuit contained He-O2 rather than O2. In summary, He-O2 mixtures in the circuit increased aerosol delivery for both MDIs and nebulizers in the mechanically ventilated model by as much as 50%. In conclusion, at appropriate flow rates and concentrations, He-O2 in the ventilator circuit may improve aerosol delivery in mechanically ventilated patients with severe airway obstruction.

Separation of alveolar surfactant into subtypes. A comparison of methods.

Alveolar surfactant is known to exist in several morphologic forms or subtypes which have been separated from bronchoalveolar lavage fluid (BAL) by two types of methods-differential centrifugation (DC) and equilibrium buoyant density gradient centrifugation (EBDC). DC separates BAL into large aggregates (LA) and small aggregates (SA); EBDC separates BAL into three peaks called ultraheavy (UH), heavy (H), and light (L). We compared these two separation methods by subjecting replicates of the same pools of BALF from groups of mice to DC and EBDC in parallel assays. We found that each method was highly internally consistent, but that the amount of phospholipid in the LA fraction of DC was consistently and substantially less (by 33 to 43%) than that found in the UH + H fractions of EBDC. This appeared to be due to failure of DC to sediment all of the phospholipid that banded as UH or H in EBDC despite adjustments in the time and g-force of DC. In experiments where differentially labeled purified H and L subtypes were subjected to DC over a wide range of g-force and time conditions, cross-contamination of the DC pellet and supernatant with heterologous subtypes was always present (4 to 33% cross-contamination). Addition of extraneous serum proteins to the BAL, as a model of lung damage, resulted in further inconsistencies in DC but not EBDC. Investigators may wish to bear these considerations in mind when planning or interpreting the results of experiments bearing on surfactant subtype analysis.

Special problems in aerosol delivery: artificial airways.

Several factors interact in influencing aerosol deposition during mechanical ventilation. Among these factors, the artificial airway is a significant barrier for aerosol deposition. Earlier studies overemphasized the impediments created by the artificial airway to aerosol delivery, because the aerosol generator was placed adjacent to the endotracheal tube or was connected to it. When the aerosol generator is placed away from the endotracheal tube, the fraction that deposits within the tube is reduced and greater aerosol deposition occurs in the lungs. The type of aerosol generator used and the ventilator settings have a greater effect than the size of the tube on the amount of aerosol that deposits in the artificial airway. To minimize aerosol loss within artificial airways, an endotracheal tube of the appropriate size should be selected. "Priming" the tube with a few doses of aerosol before use decreases the electrostatic charge on its walls and may reduce aerosol deposition within the tube. Similarly, using a spacer with the MDI, and placement of the combination in the inspiratory limb at a distance of at least 15 cm from the endotracheal tube reduces aerosol loss within the endotracheal tube. Use of nebulizers that produce submicronic aerosols, and placing them closer to the ventilator instead of closer to the patient also decreases aerosol impaction in the artificial airway. Use of a low inspiratory flow (30-60 L/min in adults), higher duty cycle (> 0.3), and helium-oxygen mixture instead of air or oxygen are other measures to reduce aerosol loss in the airway and thereby improve aerosol delivery to the lower respiratory tract of mechanically ventilated patients.

Is dipalmitoylphosphatidylcholine a substrate for convertase?

Convertase has homology with carboxylesterases, but its substrate(s) is not known. Accordingly, we determined whether dipalmitoylphosphatidylcholine (DPPC), the major phospholipid in surfactant, was a substrate for convertase. We measured [(3)H]choline release during cycling of the heavy subtype containing [(3)H]choline-labeled DPPC with convertase, phospholipases A(2), B, C, and D, liver esterase, and elastase. Cycling with liver esterase or peanut or cabbage phospholipase D produced the characteristic profile of heavy and light peaks observed on cycling with convertase. In contrast, phospholipases A(2), B, and C and yeast phospholipase D produced a broad band of radioactivity across the gradient without distinct peaks. [(3)H]choline was released when natural surfactant containing [(3)H]choline-labeled DPPC was cycled with yeast phospholipase D but not with convertase or peanut and cabbage phospholipases D. Similarly, yeast phospholipase D hydrolyzed [(3)H]choline from [(3)H]choline-labeled DPPC after incubation in vitro, whereas convertase, liver esterase, or peanut and cabbage phospholipases D did not. Thus convertase, liver esterase, and plant phospholipases D did not hydrolyze choline from DPPC either on cycling or during incubation with enzyme in vitro. In conclusion, conversion of heavy to light subtype of surfactant by convertase may require a phospholipase D type hydrolysis of phospholipids, but the substrate in this reaction is not DPPC.

Aerosol therapy for asthma.

Inhaled drugs play an important role in asthma management. The correct use of an appropriate delivery device is necessary to achieve the desired therapeutic effects of the drug. Currently, chlorofluorocarbon-propelled metered-dose inhalers, with or without spacers, are the most popular aerosol delivery devices. With the planned phase out of the chlorofluorocarbon metered-dose inhalers, the use of other delivery devices is being emphasized. To achieve optimal therapeutic effects, the drug and the delivery device should be considered a "couple". Aerosol delivery devices should provide an adequate "drug dose to the lung", be cost effective, simple to operate, minimize oropharyngeal deposition and systemic side effects, and match the patient's requirements. A new generation of aerosol delivery devices, incorporating the latest advances in aerosol technology, is likely to fulfill many of the goals mentioned above.

Aerosol therapy in mechanically ventilated patients: recent advances and new techniques.

Therapeutic aerosols are commonly used in mechanically ventilated patients, yet information regarding their efficacy and optimal technique of administration has been limited. The advantages of aerosol therapy include a smaller dose, efficacy comparable with that observed with systemic administration of the drug, and a rapid onset of action. Inhaled drugs are delivered directly to the respiratory tract, their systemic absorption is limited, and systemic side effects are minimized. Inhaled bronchodilators are routinely used with mechanically ventilated patients in the intensive care unit, but a variety of drugs ranging from antibiotics to surfactants has been administered. Nebulizers and metered-dose inhalers (MDIs) are commonly used aerosol generators because they produce respirable particles with a mass median aerodynamic diameter (MMAD) between 1 and 5 mum. Due to the limitation of available formulations, MDIs are chiefly used to deliver bronchodilators and steroids, whereas nebulizers have greater versatility and can be used to administer bronchodilators, antibiotics, surfactant, mucokinetic agents, and other drugs. The delivery of inhaled drugs in mechanically ventilated patients differs from that in ambulatory patients in several respects. Until recently, the consensus of opinion was that the efficiency of aerosol delivery to the lower respiratory tract in mechanically ventilated patients was much lower that that in ambulatory patients. Data suggest that this might be overly pessimistic and that the endotracheal tube may actually facilitate greater aerosol delivery compared with the normal airway when a variety of variables effecting aerosol delivery during mechanical ventilation are optimized.

Preferential pulmonary retention of (S)-albuterol after inhalation of racemic albuterol.

The (R)-enantiomer of racemic albuterol produces bronchodilation, whereas the (S)-enantiomer may increase airway reactivity. After oral or intravenous administration of racemic albuterol, the (R)- enantiomer is metabolized several times faster than the (S)-enantiomer; however, enantiomer disposition after inhaling racemic albuterol with a metered-dose inhaler (MDI) is not known. Accordingly, 10 healthy subjects inhaled racemic albuterol with a MDI alone and with a MDI and holding chamber. We measured plasma levels of unchanged (R)- and (S)-albuterol before and up to 4 h after inhalation of racemic albuterol, and determined the unchanged R/S ratio in urine before and at 0.5, 4, 8, and 24 h later. The disposition of albuterol's enantiomers with a MDI and holding chamber was similar to that with a MDI alone. The area under the curve (AUC) of the plasma levels over time was significantly lower for the (S)- than for the (R)-enantiomer-395.5 +/- 141.0 (SE) versus 882.7 +/- 126.4 ng. ml(-)(1). min (p < 0.05)-indicating preferential retention of (S)-albuterol in the lung. The R/S ratio in urine at 0. 5 h after albuterol was > 1, reflecting the higher plasma level of the (R)-enantiomer. In conclusion, preferential retention of the (S)- compared with the (R)-enantiomer in the lung could lead to accumulation of the (S)-enantiomer after long-term use of racemic albuterol.