The delivery of therapeutic aerosols through endotracheal tubes

Indian Guidelines on Nebulization Therapy

Inhalational therapy, today, happens to be the mainstay of treatment in obstructive airway diseases (OADs), such as asthma, chronic obstructive pulmonary disease (COPD), and is also in the present, used in a variety of other pulmonary and even non-pulmonary disorders. Hand-held inhalation devices may often be difficult to use, particularly for children, elderly, debilitated or distressed patients. Nebulization therapy emerges as a good option in these cases besides being useful in the home care, emergency room and critical care settings. With so many advancements taking place in nebulizer technology; availability of a plethora of drug formulations for its use, and the widening scope of this therapy; medical practitioners, respiratory therapists, and other health care personnel face the challenge of choosing appropriate inhalation devices and drug formulations, besides their rational application and use in different clinical situations. Adequate maintenance of nebulizer equipment including their disinfection and storage are the other relevant issues requiring guidance. Injudicious and improper use of nebulizers and their poor maintenance can sometimes lead to serious health hazards, nosocomial infections, transmission of infection, and other adverse outcomes. Thus, it is imperative to have a proper national guideline on nebulization practices to bridge the knowledge gaps amongst various health care personnel involved in this practice. It will also serve as an educational and scientific resource for healthcare professionals, as well as promote future research by identifying neglected and ignored areas in this field. Such comprehensive guidelines on this subject have not been available in the country and the only available proper international guidelines were released in 1997 which have not been updated for a noticeably long period of over two decades, though many changes and advancements have taken place in this technology in the recent past. Much of nebulization practices in the present may not be evidence-based and even some of these, the way they are currently used, may be ineffective or even harmful. Recognizing the knowledge deficit and paucity of guidelines on the usage of nebulizers in various settings such as inpatient, out-patient, emergency room, critical care, and domiciliary use in India in a wide variety of indications to standardize nebulization practices and to address many other related issues; National College of Chest Physicians (India), commissioned a National task force consisting of eminent experts in the field of Pulmonary Medicine from different backgrounds and different parts of the country to review the available evidence from the medical literature on the scientific principles and clinical practices of nebulization therapy and to formulate evidence-based guidelines on it. The guideline is based on all possible literature that could be explored with the best available evidence and incorporating expert opinions. To support the guideline with high-quality evidence, a systematic search of the electronic databases was performed to identify the relevant studies, position papers, consensus reports, and recommendations published. Rating of the level of the quality of evidence and the strength of recommendation was done using the GRADE system. Six topics were identified, each given to one group of experts comprising of advisors, chairpersons, convenor and members, and such six groups (A-F) were formed and the consensus recommendations of each group was included as a section in the guidelines (Sections I to VI). The topics included were: A. Introduction, basic principles and technical aspects of nebulization, types of equipment, their choice, use, and maintenance B. Nebulization therapy in obstructive airway diseases C. Nebulization therapy in the intensive care unit D. Use of various drugs (other than bronchodilators and inhaled corticosteroids) by nebulized route and miscellaneous uses of nebulization therapy E. Domiciliary/Home/Maintenance nebulization therapy; public & health care workers education, and F. Nebulization therapy in COVID-19 pandemic and in patients of other contagious viral respiratory infections (included later considering the crisis created due to COVID-19 pandemic). Various issues in different sections have been discussed in the form of questions, followed by point-wise evidence statements based on the existing knowledge, and recommendations have been formulated.

In vitro evaluation of aerosol delivery of aztreonam lysine (AZLI): an adult mechanical ventilation model

BACKGROUND

The delivery profile of Aztreonam lysine (AZLI) during mechanical ventilation (MV) is unknown. We evaluated the amount of AZLI drug delivered using an in vitro model of adult MV.

METHODS

An adult lung model designed to mimic current clinical practice was used. Both nebulizers were placed before a Y-piece and 4 settings were tested: A) Aeroneb solo® [AS] with a t-piece; B) AS with the spacer; C) M-Neb® [MN] with a t-piece and D) MN with the spacer. Performance was evaluated in terms of: 1) Mass median aerodynamic diameter (MMAD); 2) Geometric standard deviation (GSD), 3) Fine particle dose (FPD), 4) Fine particle fraction (FPF), 5) Inhalable mass (IM), and 6) Recovery rate (RR).

RESULTS

Both devices showed an adequate delivery of AZLI during MV, with MMAD between 2.4-2.5 µm and 87% of FPF. The FPD (38.8 and 31.7), IM (44.8 and 36.1) and RR (30 and 24) were similar for AS and MN respectively. Nebulizer aerosol delivery increased (50 and 70% respectively) for both nebulizers when using the spacer.

CONCLUSION

Both AS and MN showed a good aerosol delivery profile for AZLI during in vitro mechanical ventilation. Better aerosol delivery performance was obtained using the spacer.

Current options in aerosolised drug therapy for children receiving respiratory support

Inhalation of aerosolised medications are the mainstay of treatment for a number of chronic lung diseases and have several advantages over systemically-administered medications. These include more rapid onset of action for drugs such as β-adrenergic agonists when compared with oral medication, high luminal doses for inhaled antibiotics when used to treat endobronchial infection, and an improved therapeutic index compared with systemic delivery for these and other classes of drugs such as corticosteroids. The use of aerosolised drugs to treat patients whose tracheas are intubated is less well established, in part because systemic delivery via the intravenous route can be a simpler alternative for many drugs. Consequently, research in this area is largely limited to a number of in vitro studies and very few clinical trials. Unfortunately, a lack of focus in this area has resulted in a number of practices which at best are ineffective, and at worst dangerous for the patient. Although there have been some attempts to re-invigorate research in order to improve delivery systems, current devices are, to a great extent, based on long-standing technology developed more than 50 years ago. In this review, we explore current knowledge and provide guidance as to when and how the inhaled route may be of value when treating patients whose tracheas are intubated, and we set out the challenges facing those attempting to advance the topic. We conclude by reviewing current areas of interest that may lead to more effective and widespread use of aerosols in the treatment of intubated patients.

In Vitro Comparison of a Vibrating Mesh Nebulizer Operating in Inspiratory Synchronized and Continuous Nebulization Modes During Noninvasive Ventilation

Backround: Coupling nebulization with noninvasive ventilation (NIV) has been shown to be effective in patients with respiratory diseases. However, a breath-synchronized nebulization option that could potentially improve drug delivery by limiting drug loss during exhalation is currently not available on bilevel ventilators. The aim of this in vitro study was to compare aerosol delivery of amikacin with a vibrating mesh nebulizer coupled to a single-limb circuit bilevel ventilator, using conventional continuous (Conti-Neb) and experimental inspiratory synchronized (Inspi-Neb) nebulization modes.

METHODS

Using an adult lung bench model of NIV, we tested a vibrating mesh device coupled with a bilevel ventilator in both nebulization modes. Inspi-Neb delivered aerosol only during the whole inspiratory phase, whereas Conti-Neb delivered aerosol continuously. The nebulizer was charged with amikacin solution (250 mg/3 mL) and placed at two different positions: between the lung and exhalation port and between the ventilator and exhalation port. Inhaled, expiratory wasted and circuit lost doses were assessed by residual gravimetric method. Particle size distribution of aerosol delivered at the outlet of the ventilator circuit during both nebulization modes was measured by laser diffraction method.

RESULTS

Regardless of the nebulizer position, Inspi-Neb produced higher inhaled dose (p < 0.01; +6.3% to +16.8% of the nominal dose), lower expiratory wasted dose (p < 0.05; -2.7% to -42.6% of the nominal dose), and greater respirable dose (p < 0.01; +8.4% to +15.2% of the nominal dose) than Conti-Neb. The highest respirable dose was found with the nebulizer placed between the lung and exhalation port (48.7% ± 0.3% of the nominal dose).

CONCLUSIONS

During simulated NIV with a single-limb circuit bilevel ventilator, the use of inspiratory synchronized vibrating mesh nebulization improves respirable dose and reduces drug loss of amikacin compared with continuous vibrating mesh nebulization.

Influence of Tracheostomy on Lung Deposition in Spontaneously Breathing Patients

BACKGROUND

Nebulized drugs are frequently administrated through tracheostomy in clinical routine. So far, the amount of drug deposited into the lung in these patients remains unknown. The aim of our pharmacokinetic study was to compare lung delivery of amikacin in the same subjects in two settings: spontaneously breathing through a tracheostomy and through the mouth.

METHODS

Lung delivery was measured by amikacin urinary drug concentration in nine patients who were transitory tracheostomized for the need of a head and neck oncologic surgery. Patients performed two nebulization sessions: with a mouthpiece (MB) and through tracheostomy (TB) using a adapted jet nebulizer (Sidestream^®).

RESULTS AND CONCLUSION

Lung delivery was similar with the two conditions of nebulization (6.5 ± 2.5% vs. 6.3 ± 2.0% of the nominal mass of amikacin, respectively, for MB and TB; p = 0.95). Duration of nebulization was also comparable (19.7 ± 1.6 vs. 20.1 ± 1.8 min, respectively, for mouth and tracheostomy breathing; p = 0.307). The half-life and elimination rate constant were not different between the two settings. We conclude that nebulized therapy can be administered in spontaneously breathing tracheostomized adults patients, with a similar amount of drug delivered to the lung compared with spontaneously mouth breathing patients.

Nebulizers for drug delivery to the lungs

INTRODUCTION

Nebulizers are the oldest modern method of delivering aerosols to the lungs for the purpose of respiratory drug delivery. While use of nebulizers remains widespread in the hospital and home setting, certain newer nebulization technologies have enabled more portable use. Varied fundamental processes of droplet formation and breakup are used in modern nebulizers, and these processes impact device performance and suitability for nebulization of various formulations.

AREAS COVERED

This review first describes basic aspects of nebulization technologies, including jet nebulizers, various high-frequency vibration techniques, and the use of colliding liquid jets. Nebulizer use in hospital and home settings is discussed next. Complications in aerosol droplet size measurement owing to the changes in nebulized droplet diameters due to evaporation or condensation are discussed, as is nebulization during mechanical ventilation.

EXPERT OPINION

While the limelight may often appear to be focused on other delivery devices, such as pressurized metered dose and dry powder inhalers, the ease of formulating many drugs in water and delivering them as aqueous aerosols ensures that nebulizers will remain as a viable and relevant method of respiratory drug delivery. This is particularly true given recent improvements in nebulizer droplet production technology.

Optimal delivery of aerosols to infants during mechanical ventilation

PURPOSE

The objective of this study was to determine optimal aerosol delivery conditions for a full-term (3.6 kg) infant receiving invasive mechanical ventilation by evaluating the effects of aerosol particle size, a new wye connector, and timing of aerosol delivery.

METHODS

In vitro experiments used a vibrating mesh nebulizer and evaluated drug deposition fraction and emitted dose through ventilation circuits containing either a commercial (CM) or new streamlined (SL) wye connector and 3-mm endotracheal tube (ETT) for aerosols with mass median aerodynamic diameters of 880 nm, 1.78 μm, and 4.9 μm. The aerosol was released into the circuit either over the full inhalation cycle (T1 delivery) or over the first half of inhalation (T2 delivery). Validated computational fluid dynamics (CFD) simulations and whole-lung model predictions were used to assess lung deposition and exhaled dose during cyclic ventilation.

RESULTS

In vitro experiments at a steady-state tracheal flow rate of 5 L/min resulted in 80-90% transmission of the 880-nm and 1.78-μm aerosols from the ETT. Based on CFD simulations with cyclic ventilation, the SL wye design reduced depositional losses in the wye by a factor of approximately 2-4 and improved lung delivery efficiencies by a factor of approximately 2 compared with the CM device. Delivery of the aerosol over the first half of the inspiratory cycle (T2) reduced exhaled dose from the ventilation circuit by a factor of 4 compared with T1 delivery. Optimal lung deposition was achieved with the SL wye connector and T2 delivery, resulting in 45% and 60% lung deposition for optimal polydisperse (∼1.78 μm) and monodisperse (∼2.5 μm) particle sizes, respectively.

CONCLUSIONS

Optimization of selected factors and use of a new SL wye connector can substantially increase the lung delivery efficiency of medical aerosols to infants from current values of <1-10% to a range of 45-60%.

Albuterol delivery via metered dose inhaler in a spontaneously breathing pediatric tracheostomy model

RATIONALE

Little data are available regarding efficiency of drug delivery devices and techniques despite their widespread use in spontaneously breathing tracheostomized patients. We compared patient dose achieved with different devices, inhalation techniques, tracheostomy tube sizes and breathing patterns using a spontaneously breathing tracheostomized pediatric model.

METHODS

A tracheostomy model was connected in series to a breathing simulator with a filter interposed (patient dose). Breathing patterns of a 16-month-old and a 6- and 12-year-old child with tracheostomy with internal diameters (mm) of 3.5, 4.5, and 5.5 were used. Albuterol HFAp MDI was used. Aerotrach Plus, MediBag, Aerochamber MV, Aerochamber Mini, and inline adapter with 6-inch tubing were tested. The latter 3 devices were also tested with assisted technique. Albuterol was analyzed via spectrophotometry.

RESULTS

Aerotrach Plus outperformed almost all devices tested. Aerochamber MV with unassisted technique was the second best and the adapter was the worst. Comparison of efficiency between best and worst performer ranged from 3- to 17.2-fold. The 16-month-old breathing pattern and the 3.5 mm tracheostomy tube had the lowest patient dose. The use of assisted technique decreased patient dose by 18-67% for the 4.5 and 5.5 mm but not for 3.5 mm tracheostomy tubes. A median of 7.4% of the nominal dose was deposited in the tracheostomy tubes.

CONCLUSIONS

Aerotrach Plus and the adapter were the most and least efficient devices respectively. Tracheostomy size and breathing pattern affected drug delivery. The use of assisted technique reduced aerosol delivery.

Severe intraoperative bronchospasm treated with a vibrating-mesh nebulizer

Bronchospasm and status asthmaticus are two of the most dreaded complications that a pediatric anesthesiologist may face. With the occurrence of severe bronchospasm and the inability to ventilate, children are particularly vulnerable to apnea and ensuing hypoxia because of their smaller airway size, smaller lung functional residual capacity, and higher oxygen consumption rates than adults. Nebulized medication delivery in intubated children is also more difficult because of smaller endotracheal tube internal diameters. This case demonstrates the potentially lifesaving use of a vibrating-mesh membrane nebulizer connected to the anesthesia circuit for treating bronchospasm.

Aerosol delivery through tracheostomy tubes: an in vitro study

BACKGROUND

Our study investigated the influence of the cannula's inner diameter (ID) and of its removal on the expected respiratory dose of amikacin, using three different jet nebulizer configurations (Sidestream(®)): vented (N1), unvented with a piece of corrugated tubing attached to the expiratory limb of the T attachment (N2), and unvented alone (N3).

METHODS

The jet nebulizer was filled with amikacin (500 mg/4 mL) and was attached to the tracheostomy tube. A lung model simulating spontaneous breathing was connected to the tracheostomy tube. A filter was connected between the nebulizer and the tracheostomy tube to measure the inhaled dose, and between the tracheostomy tube and the lung model to measure the respiratory dose. Different cannula IDs were tested (6.5, 8, 8.5, and 10 mm), and aerosol lost in the cannulas was determined.

RESULTS AND CONCLUSIONS

Respiratory dose varied between 96±1 mg and 44±3 mg, with higher values observed with N2. The aerosol lost in the cannula was significant and represented up to 63% of the inhaled dose. There was a negative correlation between the cannula's ID and the aerosol lost in the cannula. After removal of the internal cannula, an increase in the respiratory dose of up to 31.3% was observed. We recommend removing the inner tracheostomy cannula to nebulize a larger amount of drug through a tracheostomy tube. Among the three jet nebulizer configurations studied, we recommend the unvented one with a piece of corrugated tubing attached to the expiratory limb of the T attachment.

Aerosol delivery to ventilated newborn infants: historical challenges and new directions

There are several aerosolized drugs which have been used in the treatment of neonatal respiratory illnesses, such as bronchodilators, diuretics, and surfactants. Preclinical in vitro and in vivo studies identified a number of variables that affect aerosol efficiency, including particle size, aerosol flows, nebulizer choice, and placement. Nevertheless, an optimized aerosol drug delivery system for mechanically ventilated infants still does not exist. Increasing interest in this form of drug delivery requires more controlled and focused research of drug/device combinations appropriate for the neonatal population. In the present article, we review the research that has been conducted thus far and discuss the next steps in developing the optimal aerosol delivery system for use in mechanically ventilated neonates.

Pulmonary Drug Delivery System for inhalation therapy in mechanically ventilated patients

The Pulmonary Drug Delivery System (PDDS) Clinical represents a newer generation of electronic nebulizers that employ a vibrating mesh or aperture plate to generate an aerosol. The PDDS Clinical is designed for aerosol therapy in patients receiving mechanical ventilation. The components of the device include a control module that is connected to the nebulizer/reservoir unit by a cable. The nebulizer contains Aerogen's OnQ aerosol generator. A pressure sensor monitors the pressure in the inspiratory limb of the ventilator circuit and provides feedback to the control module. Based on the feedback from the pressure sensor, aerosol generation occurs only during a specific part of the respiratory cycle. In bench models, the PDDS Clinical has high efficiency for aerosol delivery both on and off the ventilator, with a lower respiratory tract delivery of 50-70% of the nominal dose. Currently, the PDDS Clinical is being evaluated for the treatment of ventilator-associated pneumonia with aerosolized amikacin, an aminoglycoside antibiotic. Preliminary studies in patients with ventilator-associated pneumonia found that the administration of amikacin via PDDS reduced the need for concomitant intravenous antibiotics; however, more definitive clinical studies are needed. The PDDS Clinical delivers a high percentage of the nominal dose to the lower respiratory tract, and is well suited for inhalation therapy in mechanically ventilated patients.

Therapeutic potential of inhaled p38 mitogen-activated protein kinase inhibitors for inflammatory pulmonary diseases

BACKGROUND

Over the past two decades, p38 MAPK (mitogen-activated protein kinase) has been the subject of intense multidisciplinary research. p38 MAPK inhibitors have been shown to be efficacious in several disease models, including rheumatoid arthritis, psoriasis, Crohn's disease, and stroke. Recent studies support a role for p38 MAPK in the development, maintenance, and/or exacerbation of a number of pulmonary diseases, such as asthma, cystic fibrosis, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD).

OBJECTIVE

Many previous attempts to develop p38 MAPK inhibitors have failed as a result of unacceptable safety profiles. These toxicities have been varied and are believed to derive from different off-target effects.

METHOD

The above concerns can be overcome by delivering the compound locally to minimize whole-body burden, resulting in low exposure to the gastrointestinal, liver, and CNS. This review discusses the role of p38 MAPK in various inflammatory diseases, followed by the toxicity concerns associated with p38 MAPK inhibition. It also highlights the possible beneficial effect of delivering drugs via the inhalation route.

CONCLUSION

We present proof-of-principle confirming the therapeutic potential of inhaled p38 inhibitors for asthma and other inflammatory pulmonary diseases.

How best to deliver aerosol medications to mechanically ventilated patients

Pressurized metered-dose inhalers (pMDIs) and nebulizers are employed routinely for aerosol delivery to ventilator-supported patients, but the ventilator circuit and artificial airway previously were thought to be major barriers to effective delivery of aerosols to patients receiving mechanical ventilation. In the past two decades, several investigators have shown that careful attention to many factors, such as the position of the patient, the type of aerosol generator and its configuration in the ventilator circuit, aerosol particle size, artificial airway, conditions in the ventilator circuit, and ventilatory parameters, is necessary to optimize aerosol delivery during mechanical ventilation. The best techniques for aerosol delivery during noninvasive positive-pressure ventilation are not well established as yet, and the efficiency of aerosol delivery in this setting is lower than that during invasive mechanical ventilation. The most efficient methods of using the newer hydrofluoroalkane-pMDIs and vibrating mesh nebulizers in ventilator-supported patients also require further evaluation. When optimal techniques of administration are employed, the efficiency of aerosolized drug delivery in mechanically ventilated patients is comparable to that achieved in ambulatory patients.

Aerosol delivery during mechanical ventilation: from basic techniques to new devices

Pressurized metered-dose inhalers (pMDIs) and nebulizers are routinely employed for aerosol delivery in mechanically ventilated patients. A significant proportion of the aerosol deposits in the ventilator circuit and artificial airway, thereby reducing the inhaled drug mass. Factors influencing aerosol delivery during mechanical ventilation differ from those in spontaneously breathing patients. The English language literature on aerosol delivery during mechanical ventilation was reviewed. Marked variations in the efficiency of drug delivery with pMDIs and nebulizers occur due to differences in the technique of administration. Careful attention to five factors, viz., the aerosol generator, aerosol particle size, conditions in the ventilator circuit, artificial airway, and ventilator parameters, is necessary to optimize aerosol delivery during mechanical ventilation. Factors influencing drug delivery during NPPV are not well understood, and the efficiency of aerosol delivery in this setting is lower than that during invasive mechanical ventilaiton. With an optimal technique of administration the efficiency of aerosol delivery during mechanical ventilation is similar to that achieved during spontaneous breathing. Further research is needed to optimize aerosol delivery during NPPV.

Lung deposition of HFA beclomethasone dipropionate in an animal model of bronchopulmonary dysplasia

The best delivery of a drug in ventilated neonates is obtained when using a small particle diameter solution administered via a spacer. Lung deposition of hydrofluoroalkane beclomethasone dipropionate (QVAR, 1.3 microm particles), delivered via an Aerochamber-MV15, was measured in piglets under conditions mimicking ventilated severely ill neonates (uncuffed 2.5 mm endotracheal tube; peak pressure 16 cm H2O; respiratory rate 40/min). After determining the mass and particle size distribution of the 99mTc-labeled and unlabeled drug, three lung deposition studies were performed: after 1 h of ventilation (controls, n = 18), after 48 h aggressive ventilation inducing an acute lung injury (nine piglets out of the controls), and after increasing the pressure to 24 cm H2O during drug delivery (five piglets out of the nine with acute lung injury). All piglets were then killed for lung histology. Results (median, range), expressed as a percentage of the delivered dose, were compared using an inferential or the Friedman test. While lung deposition was low, it was greater (p = 0.003) in controls (2.66%, 0.50-7.70) than in piglets with histologically confirmed acute lung injury (0.26%, 0.06-1.28) or under a high-pressure ventilation (1.01%, 0.30-2.15). Lung deposition of QVAR in an animal model of ventilated neonates is low, variable, and dramatically affected by lung injury.

Factors Influencing the In Vitro Deposition of Tobramycin Aerosol: A Comparison of an Ultrasonic Nebulizer and a High-Frequency Vibrating Mesh Nebulizer

The aim of the study was to elaborate recommendations for inhalation during mechanical ventilation that could optimize delivery. Delivery of aerosols in vitro from nebulizers during mechanical ventilation is dependent on the dimensions of the ventilator circuit, the nebulizer type, and the ventilator settings. A review of the literature shows that some ventilator settings have a larger influence on the amount of aerosol delivered than others. It has been shown in an in vitro model that the factors influencing delivered aerosol are the ventilator flow rate, the diameter of the endotracheal tube, and the time spent in inspiration (all p < 0.05). Two different nebulizer types were used in the study: an ultrasonic nebulizer (SUN 345) and a high-frequency vibrating mesh nebulizer (Aeroneb Pro). No difference in the amount delivered was seen with different nebulizer types (p = 0.215). For optimizing the amount delivered, the largest possible flow, endotracheal tube, and time spent in inspiration should be used.

Aerosol deposition in neonatal ventilation

Lung deposition of inhaled drugs in ventilated neonates has been studied in models of questionable relevance. With conventional nebulizers, pulmonary deposition has been limited to 1% of the total dose. The objective of this study was to assess lung delivery of aerosols in a model of neonatal ventilation using a conventional and novel electronic micropump nebulizer. Aerosol deposition studies with 99mTc diethylenetriamine pentaacetate (99mTc-DTPA) were performed in four macaques (2.6 kg) that were ventilated through a 3.0-mm endotracheal tube (with neonatal settings (peak inspiratory pressure 12-14 mbar, positive end-expiratory pressure 2 mbar, I/E ratio 1/2, respiratory rate 40/min), comparing a jet-nebulizer MistyNeb (3-mL charge, 4.8 microm), an electronic micropump nebulizer operating continuously [Aeroneb Professional Nebulizer (APN-C); 0.5-mL charge, 4.6 microm], and another synchronized with inspiration [Aeroneb Professional Nebulizer Synchronized (APN-S); 0.5-mL charge, 2.8 microm]. The amount of radioactivity deposited into lungs and connections and remaining in the nebulizer was measured by a gamma counter. Despite similar amounts of 99mTc-DTPA in the respiratory circuit with all nebulizers, both APN-S and APN-C delivered more drug to the lungs than MistyNeb (14.0, 12.6, and 0.5% in terms of percentage of nebulizer charge, respectively; p = 0.006). Duration of delivery was shorter with APN-C than with the two other nebulizers (2 versus 6 and 10 min for the APN-S and the MistyNeb, respectively; p < 0.001). Electronic micropump nebulizers are more efficient to administer aerosols in an animal model of ventilated neonates. Availability of Aerogen's electronic micropump nebulizers offers new opportunities to study clinical efficacy and risks of aerosol therapy in ventilated neonates.

In vitro study and semiempirical model for aerosol delivery control during mechanical ventilation

The object of this study was to evaluate in vitro the influence of various ventilatory parameters on the delivery of synchronized nebulization of terbutaline during mechanical ventilation and to determine a semiempirical model to control the quantity of aerosol delivered into the patient's lung. An ATOMISOR NL9 M jet nebulizer (La Diffusion Technique Francaise, France) was filled with terbutaline (Bricanyl, Astra-Zeneca, Sweden) and connected to the inspiratory line of a Horus ventilator (Taema, France). Nebulization was synchronized with the inspiratory phase. We assessed at the end of the endotracheal tube the quantity of terbutaline (terbutaline mass output) and the volume median diameter (VMD) by diffraction-laser method. There was a negative correlation between terbutaline mass output and inspiratory air flow ( r =-0.95, p <0.0001) and between VMD and inspiratory air flow ( r =-0.96, p <0.0001). Moreover, positive end-expiratory pressure levels between 0 cm and 8 cm of water did not significantly change the terbutaline output mass ( p =0.22). Total nebulization time and terbutaline mass output calculated by the mathematical model showed good agreement with experimental data. In conclusion, our semiempirical model allows calculation of the duration of the nebulization required to deliver a given mass of terbutaline into patient lungs.

Aerosolized antimicrobial therapy in acutely ill patients

Recent data are sparking renewed interest in therapy with aerosolized antimicrobials in critically ill patients as well as other populations such as those with neutropenia, human immunodeficiency virus infection, and cystic fibrosis. Pneumonia is a common complication in these patients and is associated with substantial morbidity and increased mortality. Clinical trials evaluated aerosolized antimicrobials for the prevention and treatment of pneumonia in hospitalized patients. In addition, factors that affect the pulmonary deposition of aerosolized drugs in mechanically ventilated patients were identified.

Inhaled beta-agonists for asthma in mechanically ventilated patients

BACKGROUND

A small number of patients with acute severe asthma require intubation and positive pressure ventilation. The beneficial effects of inhaled bronchodilators on acute asthma in spontaneously breathing subjects are well established, but there remain important questions regarding inhaled beta2-agonists, for patients who are intubated and receiving ventilation.

OBJECTIVES

To determine the effects of inhaled beta-agonists on asthmatic patients who require intubation and mechanical ventilation.

SEARCH STRATEGY

Randomised controlled trials were sought from the Cochrane Airways Group Asthma Register. Primary authors and content experts were contacted to identify eligible studies and bibliographies from known reviews and texts were searched.

SELECTION CRITERIA

Randomised, controlled clinical trials involving adult patients with acute asthma, who were intubated and supported with positive pressure ventilation. Studies were to be included if patients were treated with beta2-adrenergic agonist agents and there was a comparator group treated with either placebo, no medication, or 'standard' treatment.

DATA COLLECTION AND ANALYSIS

Two reviewers independently examined all identified articles. The full text of any potentially relevant article was reviewed independently by two reviewers.

MAIN RESULTS

The search yielded 152 abstracts. Of these, four articles were identified as potential trials. None of the four trials met the inclusion criteria for the review.

REVIEWER'S CONCLUSIONS

There are no data from randomised controlled trials to provide evidence for or against current practices regarding the use of inhaled beta2-agonists in asthmatic subjects who are intubated and ventilated.

Aerosolized dornase alfa in cystic fibrosis: is there a role in the management of patients with early obstructive lung disease?

Airway inflammation and infection are present in patients with mild lung disease in cystic fibrosis (CF), suggesting the need for early treatment. In a previously reported large multicenter trial, dornase alfa improved pulmonary function and decreased the need for hospitalization in patients with CF over 5 years of age and with forced vital capacity greater than 40% predicted. We report here preliminary results of a study of dornase alfa delivered by two different nebulizer systems to patients with mild lung disease in CF and near normal lung function. Even in this mild group dornase alfa improved pulmonary function. The delivery system with the smaller droplet size tended to provide greater improvement than the system with the larger droplet size, although this difference was not satisfactorily significant. We have reviewed characteristics of nebulizers and patients' lung function that might affect efficacy of different nebulizer delivery systems. Our results indicate that treatment can improve pulmonary function in patients with mild lung disease in CF and illustrate the need for further studies in this group of patients.

Alternative routes of drug administration--advantages and disadvantages (subject review). American Academy of Pediatrics. Committee on Drugs

During the past 20 years, advances in drug formulations and innovative routes of administration have been made. Our understanding of drug transport across tissues has increased. These changes have often resulted in improved patient adherence to the therapeutic regimen and pharmacologic response. The administration of drugs by transdermal or transmucosal routes offers the advantage of being relatively painless.12 Also, the potential for greater flexibility in a variety of clinical situations exists, often precluding the need to establish intravenous access, which is a particular benefit for children.

This statement focuses on the advantages and disadvantages of alternative routes of drug administration. Issues of particular importance in the care of pediatric patients, especially factors that could lead to drug-related toxicity or adverse responses, are emphasized.

Therapeutic aerosol delivery during mechanical ventilation

OBJECTIVE

To provide an overview of aerosol drug delivery during mechanical ventilation in the pediatric and adult populations.

DATA SOURCES

Published articles and abstracts identified in a MEDLINE search (1984-July 1994) were reviewed.

STUDY SELECTION

All articles and abstracts found, including review articles, in vivo and in vitro studies, case reports, and case series pertaining to issues involving aerosol delivery during mechanical ventilation, were reviewed. No predetermined selection criteria were used to exclude studies.

DATA EXTRACTION

Percent delivery of the starting dose to either the patients or the various in vitro lung models, as well as each variable possibly affecting delivery for each study, were tabulated for each study reviewed.

DATA SYNTHESIS

The delivery of therapeutic aerosols to endotracheally intubated and mechanically ventilated patients presents a unique challenge for healthcare providers. Delivery can be affected by the diameter of the endotracheal tube and ventilator circuitry, type of ventilator, ventilator modes, type of delivery device, and how the delivery device is operated and introduced into the ventilator circuitry. The drug being aerosolized may behave differently from one delivery system to another. The proper operation of each device requires attention to positioning in the ventilator circuit as well as the mode of ventilation.

CONCLUSIONS

No apparent advantage exists for metered-dose inhalers with a large-volume adapter over jet nebulizers, as each method of delivery is capable of similar efficiency (5-15%). Sufficient attention to detail, including the use of an efficient nebulizer and/or adapter and proper placement and operating method, is required to provide optimal delivery. For bronchodilator administration, careful monitoring of outcomes will provide the most optimal dosing schedule.

Aerosol deposition in infants with cystic fibrosis

Twenty asymptomatic infants with cystic fibrosis (CF) were studied to determine the amount of radiolabeled aerosol [99m technetium diethylenetriamine penta acetic acid (Tc99m DTPA)] deposited in the respiratory system and its distribution. Aerosols were generated by jet nebulization systems that were used in the wards and the laboratory. Subjects were studied in three groups: group A (n = 10) was sedated with chloral hydrate; children inhaled an aerosol of 7.7 microns mass median diameter (MMD); group B (n = 5) was not sedated, using the same nebulization system (same aerosol particle size as group A); and group C (n = 5) was not sedated; these children inhaled an aerosol with an MMD of 3.6 microns. Normal saline plus 4 mCi of Tc99m bound to DTPA was added to each nebulizer. A closed system was used to collect the expired aerosol. Radioactivity in each infant and in the equipment was measured with a gamma camera on completion of nebulization. In groups A and B, the percentages of the total dose deposited in the lung were 0.97 +/- 0.35% and 0.76 +/- 0.36%, respectively. In group C, 2.0 +/- 0.71% was deposited in the lung (P < 0.01). Deposition in the nose, mouth, and pharynx was least in group C (P < 0.01). In groups A and B, the intrathoracic deposition occurred predominantly in the trachea and main bronchi, whereas in group C, significantly more aerosol was deposited in the lung region. There was marked inter-subject variability in the percentage of aerosol deposition within the three groups. There was no correlation between percentage of aerosol deposited in the respiratory system and age, height, or weight. Sedation did not have a significant effect on deposition of aerosol in infants. This study indicates that only a small proportion of nebulized solution is deposited in the lungs of infants and that this proportion is influenced by the particle size of the aerosol. The smaller particle size (3.6 microns MMD) was deposited in the lung better than large particles.

In vitro assessment of drug delivery through an endotracheal tube using a dry powder inhaler delivery system

BACKGROUND

Jet nubulisers and metered dose inhalers are widely used to deliver aerosolised drugs to the lungs of intubated patients in adult intensive care units. Drug delivery using these systems has been shown to be inefficient and both forms of delivery have the potential to induce paradoxical bronchoconstriction in patients with reactive airways disease.

METHODS

Experiments were carried out to determine whether it was possible to deliver drug from a dry powder delivery system through an endotracheal tube. A 200 micrograms budesonide Turbohaler was enclosed in a chamber which allowed it to be inserted into a ventilator circuit. Experiments were performed with a multistage liquid impinger in which drug was drawn through the Turbohaler and endotracheal tube at 60 l/min providing an index of the maximum drug delivery achievable via this route. A second series of experiments was performed in which the Turbohaler was placed in a ventilator circuit using a Servo 900C volume cycled ventilator. Drug delivered from the Turbohaler during the inspiratory phase was collected on a filter placed between the end of a 9 mm endotracheal tube and a model lung. A tidal volume of 500 ml and inspiratory time of 0.5 seconds was used. Budesonide was assayed using an ultraviolet spectrophotometric assay.

RESULTS

Thirty percent of the nominal dose passed through the endotracheal tube and was collected in the multistage liquid impinger. Mean drug delivery to the filter in the ventilator circuit was 20%.

CONCLUSIONS

This in vitro study indicates that drugs from dry powder inhalers (in this case the Turbohaler) can be satisfactorily delivered through endotracheal tubes and that clinical evaluation of this technique is now indicated.

The delivery of aerosolized steroids from MDIs with nozzle extensions: quantitative laboratory evaluation of a method to improve aerosol delivery to intubated patients

OBJECTIVE

Pulmonary deposition of aerosolized drug from a metered dose inhaler (MDI) is low with intubated patients. In the laboratory, extension of the MDI nozzle to the endotracheal tube tip has been shown to increase the delivered dose of albuterol. The objectives of this study were to determine the dose of aerosolized steroid (beclomethasone and triamcinolone) delivered through a MDI nozzle extension, the effect of nozzle extension length and number of actuations on the delivered dose, and particle size delivered through the nozzle extension.

DESIGN

A 19-G catheter was used as the MDI nozzle extension. The nozzle extension was attached to a 60-ml syringe via the Luer-Lok connection, and the distal end was directed through a hole drilled into a 15-ml capped tube. The MDI was placed into the syringe and actuated by pressing the syringe plunger. Drug delivered through the nozzle extension into the tube was dissolved in methanol (beclomethasone) or ethanol (triamcinolone). Nozzle extension lengths of 10 cm, 20 cm and 30 cm were studied. For each nozzle extension length, delivery was assessed using one, two, three and five actuations of each drug. Drug remaining in the nozzle extension was recovered by rinsing with the appropriate solvent. Aerosol particle size leaving the nozzle extension was determined using a seven-stage cascade impactor. Beclomethasone and triamcinolone concentrations were determined by spectrophotometry at 239 nm.

SETTING

Respiratory care laboratory of a university teaching hospital.

RESULTS

For the pooled results, 70.2 +/- 14.1% of the dose was delivered through the nozzle extension, with no difference between beclomethasone and triamcinolone (p = 0.838). The proportion of drug delivered through the 10-cm extension (76.7 +/- 8.4%) was greater than that from the 20-cm (66.1 +/- 16.5%) and 30-cm (67.7 +/- 13.9%) extensions (p = 0.001). Less drug was delivered through the extension with one actuation (54.1 +/- 17.7%) than with two (71.2 +/- 7.7%), three (77.2 +/- 5.5%), or five actuations (78.2 +/- 4.3%) (p < 0.001). There was a decrease in MMAD with increasing nozzle extension length (3.14 +/- 0.61 microns for 10 cm, 2.97 +/- 0.28 microns for 20 cm, 2.37 +/- 0.27 microns for 30 cm; p = 0.005).

CONCLUSIONS

A high proportion of aerosolized steroid was delivered with a MDI actuated through a nozzle extension. The proportion delivered through the nozzle extension was significantly less with longer nozzle extensions and with fewer actuations, but this may not be clinically important. Although particle sizes were smaller from longer nozzle extensions, all were within the respirable range. These results suggest that steroids can be delivered efficiently using a MDI nozzle extension.

Bronchodilator aerosol administered by metered dose inhaler and spacer in subacute neonatal respiratory distress syndrome

There is increasing evidence that bronchodilators are effective in ventilator dependent preterm infants. The effects of single doses of salbutamol (400 micrograms), ipratropium bromide (72 micrograms), and placebo (four puffs) given by metered dose inhaler and spacer (MDIS) were examined in 10 ventilated preterm infants, with a mean birth weight of 800 g at a postnatal age of 1 week, who were suffering from respiratory distress syndrome. The agents were each given in an open, random design. Blood gases were measured and ventilatory efficiency index (VEI) and arterial/alveolar oxygen tension ratio (PaO2/PAO2) were calculated five minutes before and 30 minutes after administration. Heart rate and mean arterial blood pressure were noted. The mean PaO2 improved by 0.61 kPa and 0.69 kPa after salbutamol and ipratropium bromide, respectively and these changes were significantly greater than the 0.5 kPa fall seen with placebo. The mean arterial carbon dioxide tension fell by 0.98 kPa after salbutamol and 0.59 kPa after ipratropium bromide. After both salbutamol and ipratropium bromide, VEI improved significantly (by 23% and 20% respectively) but there was no significant change in the PaO2/PAO2, suggesting that respiratory mechanics and not ventilation/perfusion balance had improved after a single dose of bronchodilator. We conclude that both salbutamol and ipratropium bromide given by MDIS have useful short term effects in ventilator dependent neonates with respiratory distress syndrome. Precise dose regimens and long term effects remain to be worked out.

Therapeutic aerosols in children

The use and variety of drugs administered to children as inhaled aerosols is increasing, but little is known about how much drug reaches the lung and how it is distributed there in different age groups. In this article the reasons for measuring aerosol deposition in children are discussed and the potential methods for doing this described. Of the methods available, only the use of radiolabelled aerosols gives accurate information on total lung deposition and distribution. The potential risk of the radiation exposure required for these measurements varies with the age of the child but seems to be small. Properly designed studies are expected to clarify the factors affecting lung deposition in children and identify methods of inhalation associated with efficient and predictable delivery of the drug. Measurements of radioaerosol deposition may therefore be justified in children when this information is expected to lead to improvements in the effectiveness or safety of their treatment.

Small bore nozzle extensions to improve the delivery efficiency of drugs from metered dose inhalers: laboratory evaluation

Metered dose inhalers (MDIs) are frequently used to supply aerosolized drugs, particularly bronchodilators, to the tracheobronchial tree of patients with endotracheal tubes in the intensive care unit or in the operating room. The efficiency of delivery to the lungs of agents such as the beta 2-adrenergic agonists is known to be low. In an in vitro model, we evaluated a means of improving the delivery of drug released from an MDI beyond the distal tip of the endotracheal tube. Extensions of the MDI nozzle were fashioned from modified intravenous catheters or sections of small bore polyethylene tubing. A model trachea/carina was constructed and suspended above a collecting device. An albuterol MDI was actuated through the nozzle extension and into the model airway. We measured the quantity of albuterol deposited in the nozzle extension, in the trachea/carina and in the distal collecting device. Particle size distribution was determined with a cascade impactor. The results indicate an inverse relationship between the quantity of drug delivered distally and the inner diameter of the nozzle extension, with a marked increase in delivery for an inner diameter < 1 mm. Ninety percent of the actuated dose from the MDI exited a 0.76-mm inner diameter nozzle extension. From 20 to 30% of the nominal MDI dose was recovered from the distal collector, 70% of which deposited in the particle size range of 1 to 5 microns. Deposition in the trachea/carina was high, but this was reduced by introducing a flare in the tip of the nozzle extension, which did not affect the dose reaching the distal collector.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary deposition of a nebulised aerosol during mechanical ventilation

BACKGROUND

There is increasing use of therapeutic aerosols in patients undergoing mechanical ventilation. Few studies have measured aerosol delivery to the lungs under these conditions with adequate experimental methods. Hence this study was performed to measure pulmonary aerosol deposition and to determine the reproducibility of the method of measurement during mechanical ventilation.

METHODS

Nine male patients were studied during mechanical ventilation after open heart surgery and two experiments were performed in each to determine the reproducibility of the method. A solution of technetium-99m labelled human serum albumin (99mTc HSA (50 micrograms); activity in experiment 1, 74 MBq; in experiment 2, 185 MBq) in 3 ml saline was administered with a Siemens Servo 945 nebuliser system (high setting) and a System 22 Acorn nebuliser unit. Pulmonary deposition was quantified by means of a gamma camera and corrections derived from lung phantom studies.

RESULTS

Pulmonary aerosol deposition was completed in 22 (SD 4) minutes. Total pulmonary deposition (% nebuliser dose (SD)) was 2.2 (0.8)% with 1.5% and 0.7% depositing in the right and left lungs respectively; 0.9% of the nebuliser activity was detected in the endotracheal tube or trachea and 51% was retained within the nebuliser unit. Considerable variability between subjects was found for total deposition (coefficient of variation (CV) 46%), but within subject reproducibility was good (CV 15%).

CONCLUSIONS

Administration of aerosol in this way is inefficient and further research is needed to find more effective alternatives in patients who require mechanical respiratory support. This method of measurement seems suitable for the assessment of new methods of aerosol delivery in these patients.

Evaluation of a reservoir device for metered-dose bronchodilator delivery to intubated adults. An in vitro study

We investigated the use of a reservoir device for delivery of a MDI bronchodilator aerosol using a lung model of an intubated, mechanically ventilated adult.

METHODS

Albuterol (Proventil) was delivered with a MDI using three methods. In method 1, the MDI was attached directly onto the ETT using a commercially available actuator/adapter. In method 2, the Monaghan AeroVent reservoir was placed on the inspiratory limb of the ventilator circuit just before the patient Y connector. In method 3, the AeroVent was placed between the patient Y connector and the ETT. Standardized ventilator settings with a Servo 900C were used for all three methods (VE = 9.6 L; respiratory rate = 12 breaths per minute; TI = 20 percent of 1 s). Aerosol drug delivery was measured at the distal tip of the ETT using a spectrophotometric technique. Percentage of amount delivered was calculated from measured delivery of the MDI.

RESULTS

The MDI directly on the ETT delivered 7.3 percent of the total dose to the end of the ETT. The AeroVent on the inspiratory limb increased this to 32.1 percent and the AeroVent between the Y connector and the ETT delivered 29 percent. Both reservoir delivery methods delivered significantly more drug than direct placement of the MDI on the ETT (p less than 0.01) but did not differ from each other (p greater than 0.05).

CONCLUSIONS

Use of the AeroVent reservoir chamber significantly increased bronchodilator delivery by aerosol with an MDI in an adult lung model of an intubated patient on ventilatory support.

Beta-adrenergic agonists for acute, severe asthma

OBJECTIVE

To critically review the use of beta-adrenergic agonists in acute, severe asthma with particular focus on aerosol administration.

DATA SOURCES

English language articles published since 1971 on the use of beta-agonists for acute asthma. Studies were identified from bibliographies of book chapters, review articles, and other research articles.

STUDY SELECTION

All studies (21 total) comparing systemic with inhaled beta-agonists were reviewed, regardless of their design or outcome. Selected studies highlighting specific aspects of beta-agonist use in acute asthma such as beta-agonists versus other bronchodilators, aerosol delivery, and intravenous beta-agonists were also reviewed.

DATA EXTRACTION

Performed subjectively by the authors with specific aspects of quality discussed within the body of the article.

DATA SYNTHESIS

The beta-agonists provide superior bronchodilation in acute severe asthma compared with either the methylxanthines and/or anticholinergics. The majority of studies found aerosolized beta-agonists to be either as effective as or more effective than parenteral beta-agonists and to produce fewer adverse cardiovascular effects. Studies showing preference for parenteral therapy have either been of poor design or used low doses of an aerosolized beta-agonist. Based on studies of aerosol delivery, there is no advantage of jet nebulization over metered-dose inhalers; however, other aspects, including ease of administration, favor nebulization as the delivery method of choice. The articles recommending intravenous beta-agonists consist of a series of uncontrolled cases.

CONCLUSIONS

Aerosolized selective beta 2-agonists are the bronchodilator treatments of choice for acute, severe asthma. Attention to the details of dosing and delivery are required for optimal results. The final dose and dosing interval are determined by the patient's response. Intravenous beta-agonists are hazardous and cannot be recommended.

Delivery of micronized budesonide suspension by metered dose inhaler and jet nebulizer into a neonatal ventilator circuit

We compared the delivery of a micronized suspension of budesonide by a metered dose inhaler (MDI) with two different spacers (Aerochamber and Aerovent) and by two jet nebulizers (MAD2 and Ultravent) to a ventilated neonatal test-lung using a standard neonatal ventilator circuit. The combination of MDI and Aerochamber was significantly better at delivering budesonide to a filter in front of the test lung (14.2% of aerosolized dose) than were either the MDI and Aerovent (3.6%) or the Ultravent or MAD2 jet nebulizers (0.02% and 0.68% of initial reservoir dose). Of the droplets emerging from the MDI, Aerochamber, and ET tube, 18% of the initial dose was in droplets less than 4.7 microns. Assuming that the test-lung model accurately reflects in vivo deposition, the combination of MDI and Aerochamber appears to be an extremely effective way of delivering budesonide aerosol to ventilated newborn infants.

The impact of changing ventilator parameters on availability of nebulized drugs in an in vitro neonatal lung system

An in vitro model was developed to assess nebulized drug delivery. The model simulated the intubated neonate and examined the effect of changes in a variety of parameters commonly confronted in the clinical setting. Theophylline was nebulized for 15 minutes and captured in an artificial lung system (a 1000-mL intravenous bag). Variables were: peak pressure (20, 24, 28 cm H2O), ventilator rate (40, 60, 80 breaths/min), nebulizer flow rate (5, 7, 10 L/min), endotracheal tube size (2.5, 3.0, 3.5 mm), and ventilator type (Servo 900C, Bourns BP 200, Bear Cub BP 2001). The amount of drug actually captured in the bag ranged from 0.009 to 12.59 percent (mean 2.08). A multivariate analysis showed that only nebulizer flow rate had a statistically significant effect on drug delivery with 10 L/min delivering the most drug. All factors combined only accounted for 11.5 percent of the variability in drug delivery. In light of the wide and unpredictable amounts of drug delivered through ventilators, dosing to pharmacologic effect rather than staying within narrow dosing guidelines may be more rational in patients responding poorly to standard doses.

Aerosol delivery in neonatal ventilator circuits: a rabbit lung model

The benefits of inhaled therapy in ventilated neonates are recognized, but the reliability of drug delivery in nebulizer-ventilator circuits is uncertain. We quantified the effect of changing variables. Twenty-three freshly killed rabbits (1.15-1.9 kg) were ventilated via a tracheostomy by a pressure-limited, time-cycled ventilator (Neovent). A radioaerosol of 99Tcm pertechnetate from an Ultravent nebulizer (Mallinkrodt) was fed into the proximal ventilator tubing. Two 3-minute nebulizations at "standard settings" were followed by 2 at altered pressure, frequency, gas flow, I:E ratio, or position of the nebulizer in the circuit. Each nebulization was followed by a 3-minute gamma camera image and total deposited radioactivity was measured in excised lungs and trachea. Images demonstrated good peripheral aerosol deposition. At standard settings, lung deposition averaged 2.8% of the aerosol released. This was decreased markedly by reducing tidal volume (ventilator pressures) and residence time of aerosol (I:E ratio). Reduced gas flow decreased deposition slightly, presumably by increased particle size and marginally reduced tidal volume. Deposition did not change with increased frequency; increased minute ventilation was offset by decreased residence time of the aerosol. We conclude that the Ultravent nebulizer can be used to nebulize drugs in a standard neonatal circuit, although the dose delivered is small. Tidal volume and aerosol residence time are important determinants of aerosol delivery.