The Effects of Inspiratory Flows, Inspiratory Pause, and Suction Catheter on Aerosol Drug Delivery with Vibrating Mesh Nebulizers During Mechanical Ventilation

Background: Some experts recommend specific ventilator settings during nebulization for mechanically ventilated patients, such as inspiratory pause, high inspiratory to expiratory ratio, and so on. However, it is unclear whether those settings improve aerosol delivery. Thus, we aimed to evaluate the impact of ventilator settings on aerosol delivery during mechanical ventilation (MV). Methods: Salbutamol (5.0 mg/2.5 mL) was nebulized by a vibrating mesh nebulizer (VMN) in an adult MV model. VMN was placed at the inlet of humidifier and 15 cm away from the Y-piece of the inspiratory limb. Eight scenarios with different ventilator settings were compared with endotracheal tube (ETT) connecting 15 cm from the Y-piece, including tidal volumes of 6-8 mL/kg, respiratory rates of 12-20 breaths/min, inspiratory time of 1.0-2.5 seconds, inspiratory pause of 0-0.3 seconds, and bias flow of 3.5 L/min. In-line suction catheter was utilized in two scenarios. Delivered drug distal to the ETT was collected by a filter, and drug was assayed by an ultraviolet spectrophotometry (276 nm). Results: Compared to the use of inspiratory pause, the inhaled dose without inspiratory pause was either higher or similar across all ventilation settings. Inhaled dose was negatively correlated with inspiratory flow with VMN placed at 15 cm away from the Y-piece (rs = -0.68, p < 0.001) and at the inlet of humidifier (rs = -0.83, p < 0.001). The utilization of in-line suction catheter reduced inhaled dose, regardless of the ventilator settings and nebulizer placements. Conclusions: When VMN was placed at the inlet of humidifier, directly connecting the Y-piece to ETT without a suction catheter improved aerosol delivery. In this configuration, the inhaled dose increased as the inspiratory flow decreased, inspiratory pause had either no or a negative impact on aerosol delivery. The inhaled dose was greater with VMN placed at the inlet of humidifier than 15 cm away the Y-piece.

Effects of Ketamine Infusion on Breathing and Encephalography in Spontaneously Breathing ICU Patients

BACKGROUND

Preclinical studies suggest that ketamine stimulates breathing. We investigated whether adding a ketamine infusion at low and high doses to propofol sedation improves inspiratory flow and enhances sedation in spontaneously breathing critically ill patients.

METHODS

In this prospective interventional study, twelve intubated, spontaneously breathing patients received ketamine infusions at 5 mcg/kg/min, followed by 10 mcg/kg/min for 1 h each. Airway flow, pressure, and esophageal pressure were recorded during a spontaneous breathing trial (SBT) at baseline, and during the SBT conducted at the end of each ketamine infusion regimen. SBT consisted of one-minute breathing with zero end-expiratory pressure and no pressure support. Changes in inspiratory flow at the pre-specified time points were assessed as the primary outcome. Ketamine-induced change in beta-gamma electroencephalogram power was the key secondary endpoint. We also analyzed changes in other ventilatory parameters respiratory timing, and resistive and elastic inspiratory work of breathing.

RESULTS

Ketamine infusion of 5 and 10 mcg/kg/min increased inspiratory flow (median, IQR) from 0.36 (0.29-0.46) L/s at baseline to 0.47 (0.32-0.57) L/s and 0.44 (0.33-0.58) L/s, respectively (p = .013). Resistive work of breathing decreased from 0.4 (0.1-0.6) J/l at baseline to 0.2 (0.1-0.3) J/l after ketamine 10 mcg/kg/min (p = .042), while elastic work of breathing remained unchanged. Electroencephalogram beta-gamma power (19-44 Hz) increased compared to baseline (p < .01).

CONCLUSIONS

In intubated, spontaneously breathing patients receiving a constant rate of propofol, ketamine increased inspiratory flow, reduced inspiratory work of breathing, and was associated with an "activated" electroencephalographic pattern. These characteristics might facilitate weaning from mechanical ventilation.

New insights into the optimal management of COPD: Extracts from CHEST 2021 annual meeting (October 17-20, 2021)

The mainstay of treatment for chronic obstructive pulmonary disease (COPD) is inhaled long-acting maintenance therapy, but discordance between real-world prescribing patterns and global treatment guidelines is increasingly being reported in the literature. Furthermore, aspects of the current treatment paradigm are subject to ongoing debate, such as when to supplement single or dual long-acting bronchodilator therapy with inhaled corticosteroids (ICS). Non-pharmacological, patient-related factors, such as inhalation technique and inspiratory flow, remain a key determinant of disease control in COPD, and over the past 18 months, new and unique challenges in the management of COPD have emerged as a result of the COVID-19 pandemic. This article summarizes a series of presentations sponsored by Boehringer Ingelheim and delivered at the annual CHEST congress 2021 (October 17-20, 2021) that explored new insights into the optimal management of COPD. These included evaluating the clinical and health-economic consequences of guideline-discordant prescribing in the US, the comparative effectiveness of dual bronchodilator therapy and ICS-containing triple therapy, the effect of disease severity and contextual factors on patient inspiratory flow, and the potential for a new digital model to revolutionize the way we conduct clinical trials in COPD in the post-COVID setting.

Lung Deposition and Inspiratory Flow Rate in Patients with Chronic Obstructive Pulmonary Disease Using Different Inhalation Devices: A Systematic Literature Review and Expert Opinion

BACKGROUND

Our aim was to describe: 1) lung deposition and inspiratory flow rate; 2) main characteristics of inhaler devices in chronic obstructive pulmonary disease (COPD).

METHODS

A systematic literature review (SLR) was conducted to analyze the features and results of inhaler devices in COPD patients. These devices included pressurized metered-dose inhalers (pMDIs), dry powder inhalers (DPIs), and a soft mist inhaler (SMI). Inclusion and exclusion criteria were established, as well as search strategies (Medline, Embase, and the Cochrane Library up to April 2019). In vitro and in vivo studies were included. Two reviewers selected articles, collected and analyzed data independently. Narrative searches complemented the SLR. We discussed the results of the reviews in a nominal group meeting and agreed on various general principles and recommendations.

RESULTS

The SLR included 71 articles, some were of low-moderate quality, and there was great variability regarding populations and outcomes. Lung deposition rates varied across devices: 8%-53% for pMDIs, 7%-69% for DPIs, and 39%-67% for the SMI. The aerosol exit velocity was high with pMDIs (more than 3 m/s), while it is much slower (0.84-0.72 m/s) with the SMI. In general, pMDIs produce large-sized particles (1.22-8 μm), DPIs produce medium-sized particles (1.8-4.8 µm), and 60% of the particles reach an aerodynamic diameter <5 μm with the SMI. All inhalation devices reach central and peripheral lung regions, but the SMI distribution pattern might be better compared with pMDIs. DPIs' intrinsic resistance is higher than that of pMDIs and SMI, which are relatively similar and low. Depending on the DPI, the minimum flow inspiratory rate required was 30 L/min. pMDIs and SMI did not require a high inspiratory flow rate.

CONCLUSION

Lung deposition and inspiratory flow rate are key factors when selecting an inhalation device in COPD patients.

Evaluation of Suboptimal Peak Inspiratory Flow in Patients with Stable COPD

Objective: Although the importance of assessing inspiratory flow in the selection of treatments for chronic obstructive pulmonary disease (COPD) is understood, evaluation of this factor is not yet widespread or standardized. The objective of the present work was to evaluate the peak inspiratory flow (PIF) of patients with COPD and to explore the variables associated with a suboptimal PIF. Methods: An observational, cross-sectional study was carried out at specialized nursing consultations over a period of 6 months. We collected clinical data as well as data on symptoms, treatment adherence, and patient satisfaction with their inhalers via questionnaires. PIF was determined using the In-Check Dial G16^® device (Clement Clarke International, Ltd., Harlow, UK). In each case, the PIF was considered suboptimal when it was off-target for any of the prescribed inhalers. The association with suboptimal PIF was evaluated using multivariate logistic regression and the results were expressed as the odds ratio (OR) with 95% confidence interval (CI). Results: A total of 122 COPD patients were included in this study, of whom 34 (27.9%) had suboptimal PIF. A total of 229 inhalers were tested, of which 186 (81.2%) were dry powder devices. The multivariate analysis found an association between suboptimal PIF and age (OR = 1.072; 95% CI (1.019, 1.128); p = 0.007) and forced vital capacity (OR = 0.961; 95% CI (0.933, 0.989); p = 0.006). Conclusions: About a third of patients in complex specialized COPD care have suboptimal PIFs, which is related to age and forced vital capacity.

[EFFECT OF INSPIRATORY FLOW ON BREATH SOUND ANALYSIS IN CHILDREN WITH ASTHMA]

BACKGROUND

In order to determine the optimal breathing method for childhood lung sound analyses, it is important to study the effect of airflow on the parameters of lung sounds.

METHODS

Sixty-one well-controlled children with atopic asthma (median; 12 years) participated. After confirming that there was no wheezing or respiratory symptoms, the lung sound spectrums of the inspiratory flow before and after inhalation of a β₂ stimulant were analyzed. At the same time, their lung function was measured by a spirogram and the forced oscillation technique.

RESULTS

Before β₂ agonist inhalation, the area under the entire curve (A_T) and 99% frequency (F₉₉) in the lung sound of inspiratory flow around 2.0L/s due to slightly strong breathing were significantly higher than the lung sound of inspiratory flow around 1.0L/s due to rest breathing. However, no marked differences were observed in the lung sound parameters based on the lung sound spectrum. The improvement in the lung sound parameters after β₂ agonist inhalation was clearer at an inspiratory flow around 1.0L/s than that around 2.0L/s.

CONCLUSION

The present study showed that changes after β₂ agonist inhalation and the correlation with the lung function parameters were clear during resting breathing. This method may be used for the long-term montoring of children with asthma.

The basics of respiratory mechanics: ventilator-derived parameters

Mechanical ventilation is a life-support system used to maintain adequate lung function in patients who are critically ill or undergoing general anesthesia. The benefits and harms of mechanical ventilation depend not only on the operator's setting of the machine (input), but also on their interpretation of ventilator-derived parameters (outputs), which should guide ventilator strategies. Once the inputs-tidal volume (V_T), positive end-expiratory pressure (PEEP), respiratory rate (RR), and inspiratory airflow (V')-have been adjusted, the following outputs should be measured: intrinsic PEEP, peak (Ppeak) and plateau (Pplat) pressures, driving pressure (ΔP), transpulmonary pressure (P_L), mechanical energy, mechanical power, and intensity. During assisted mechanical ventilation, in addition to these parameters, the pressure generated 100 ms after onset of inspiratory effort (P_0.1) and the pressure-time product per minute (PTP/min) should also be evaluated. The aforementioned parameters should be seen as a set of outputs, all of which need to be strictly monitored at bedside in order to develop a personalized, case-by-case approach to mechanical ventilation. Additionally, more clinical research to evaluate the safe thresholds of each parameter in injured and uninjured lungs is required.

Surface electromyographic evaluation of the neuromuscular activation of the inspiratory muscles during progressively increased inspiratory flow under inspiratory-resistive loading

This study aimed to evaluate neuromuscular activation in the scalene and sternocleidomastoid muscles using surface electromyography (EMG) during progressively increased inspiratory flow, produced by increasing the respiratory rate under inspiratory-resistive loading using a mask ventilator. Moreover, we attempted to identify the EMG inflection point (EMG^IP) on the graph, at which the root mean square (RMS) of the EMG signal values of the inspiratory muscles against the inspiratory flow velocity acceleration abruptly increases, similarly to the EMG anaerobic threshold (EMG^AT) reported during incremental-resistive loading in other skeletal muscles. We measured neuromuscular activation of healthy male subjects and found that the inspiratory flow velocity increased by approximately 1.6-fold. We successfully observed an increase in RMS that corresponded to inspiratory flow acceleration with ρ ≥ 0.7 (Spearman's rank correlation) in 17 of 27 subjects who completed the experimental protocol. To identify EMG^IP, we analyzed the fitting to either a straight or non-straight line related to the increasing inspiratory flow and RMS using piecewise linear spline functions. As a result, EMG^IP was identified in the scalene and sternocleidomastoid muscles of 17 subjects. We believe that the identification of EMG^IP in this study infers the existence of EMG^AT in inspiratory muscles. Application of surface EMG, followed by identification of EMG^IP, for evaluating the neuromuscular activation of respiratory muscles may be allowed to estimate the signs of the respiratory failure, including labored respiration, objectively and non-invasively accompanied using accessory muscles in clinical respiratory care.

Treatment effect of idebenone on inspiratory function in patients with Duchenne muscular dystrophy

Assessment of dynamic inspiratory function may provide valuable information about the degree and progression of pulmonary involvement in patients with Duchenne muscular dystrophy (DMD). The aims of this study were to characterize inspiratory function and to assess the efficacy of idebenone on this pulmonary function outcome in a large and well-characterized cohort of 10-18 year-old DMD patients not taking glucocorticoid steroids (GCs) enrolled in the phase 3 randomized controlled DELOS trial. We evaluated the effect of idebenone on the highest flow generated during an inspiratory FVC maneuver (maximum inspiratory flow; V'I,max(FVC)) and the ratio between the largest inspiratory flow during tidal breathing (tidal inspiratory flow; V'I,max(t)) and the V'I,max(FVC). The fraction of the maximum flow that is not used during tidal breathing has been termed inspiratory flow reserve (IFR). DMD patients in both treatment groups of DELOS (idebenone, n = 31; placebo: n = 33) had comparable and abnormally low V'I,max(FVC) at baseline. During the study period, V'I,max(FVC) further declined by -0.29 L/sec in patients on placebo (95%CI: -0.51, -0.08; P = 0.008 at week 52), whereas it remained stable in patients on idebenone (change from baseline to week 52: 0.01 L/sec; 95%CI: -0.22, 0.24; P = 0.950). The between-group difference favoring idebenone was 0.27 L/sec (P = 0.043) at week 26 and 0.30 L/sec (P = 0.061) at week 52. In addition, during the study period, IFR improved by 2.8% in patients receiving idebenone and worsened by -3.0% among patients on placebo (between-group difference 5.8% at week 52; P = 0.040). Although the clinical interpretation of these data is currently limited due to the scarcity of routine clinical practice experience with dynamic inspiratory function outcomes in DMD, these findings from a randomized controlled study nevertheless suggest that idebenone preserved inspiratory muscle function as assessed by V'I,max(FVC) and IFR in patients with DMD. Pediatr Pulmonol. 2017;52:508-515. © 2016 The Authors. Pediatric Pulmonology Published by Wiley Periodicals, Inc.

Inhalation of tobramycin using simulated cystic fibrosis patient profiles

INTRODUCTION

TOBI^® Podhaler™ is a capsule-based drug-device combination (tobramycin inhalation powder [TIP] 28 mg capsules via unit-dose dry powder T-326 Inhaler [Podhaler™]) developed for treatment of Pseudomonas aeruginosa infection in cystic fibrosis (CF). We explored how inspiratory flow profiles and mouth-throat geometries affect drug delivery with the T-326 Inhaler.

METHODS

Inspiratory flow profiles were recorded from 38 subjects aged 6-71 who had CF and varying degrees of lung function impairment. Ten of the inspiratory flow profiles were simulated in the laboratory using a custom breath simulator to determine delivered dose (DD) from the T-326 Inhaler. In vitro total lung dose (TLD_{in vitro} ) was measured using four anatomical throat models, ranging from a child to a large adult.

RESULTS

Aerosol performance was assessed across a range of inspiratory flow profiles. Mean DD ranged from 88.8% to 97.0% of declared capsule content. TLD_{in vitro} ranged from 54.8% to 72.4% of capsule content between the flow profile/throat options tested, and the mean TLD_{in vitro} across the range of flow profiles and anatomical throats tested was 63 ± 5%.

CONCLUSIONS

Our findings indicate that the T-326 Inhaler provides reliable drug delivery at flow rates likely to be achieved by a broad spectrum of patients with CF. Importantly, forceful inhalation was not required to achieve a robust TLD_{in vitro} . Pediatr Pulmonol. 2016;51:1159-1167. © 2016 Wiley Periodicals, Inc.

In Vitro Determination of Respimat® Dose Delivery in Children: An Evaluation Based on Inhalation Flow Profiles and Mouth-Throat Models

Background: Aerosol therapy in young children can be difficult. A realistic model based on handling studies and in vitro investigations can complement clinical deposition studies and be used to enable dose-to-the-lung (DTL) predictions.

Methods: Predictions on dose delivery to the lung were based on (1) representative inhalation flow profiles from children enrolled in a Respimat^® handling study, (2) in vitro measurement of the fine-particle DTL using mouth–throat models derived from nuclear magnetic resonance/computed tomography (NMR/CT) scans of children, and (3) a mathematical model to predict the tiotropium DTL. Accuracy of the prediction was confirmed using pharmacokinetic (PK) data from children with cystic fibrosis enrolled in a phase 3 clinical trial of tiotropium Respimat with valved holding chamber (VHC).

Results: Representative inhalation flow profiles for each age group were obtained from 56 children who successfully inhaled a volume >0.15 L from the Respimat with VHC. Average dimensions of the mouth–throat region for 38 children aged 1–<2 years, 2–<3 years, 3–<4 years, and 4–<5 years were determined from NMR/CT scans. The DTL from the Respimat plus VHC were determined by in vitro measurement and were 5.1±1.1%, 15.6%±1.4%, 17.9%±1.5%, and 37.1%±1.8% of the delivered dose for child models 0–<2 years, 2–<3 years, 3–<4 years, and 4–<5 years, respectively. This provides a possible explanation for the age dependence of clinical PK data obtained from the phase 3 tiotropium trial. Calculated in vitro DTL per body mass (μg/kg [±SD]) were 0.031±0.014, 0.066±0.031, 0.058±0.024, and 0.059±0.029, respectively, compared to 0.046 in adults. Therefore, efficacy of the treatment was not negatively impacted in spite of the seemingly low percentages of the DTL.

Conclusions: We conclude that the combination of real-life inhalation profiles with respective mouth–throat models and in vitro determination of delivered DTL is a good predictor of the drug delivery to children via the Respimat with VHC. The data provided can be used to support data from appropriate clinical trials.

Influence of inspiratory flow pattern and nebulizer position on aerosol delivery with a vibrating-mesh nebulizer during invasive mechanical ventilation: an in vitro analysis

BACKGROUND

Aerosol delivery during invasive mechanical ventilation (IMV) depends on nebulizer type, placement of the nebulizer and ventilator settings. The purpose of this study was to determine the influence of two inspiratory flow patterns on amikacin delivery with a vibrating-mesh nebulizer placed at different positions on an adult lung model of IMV equipped with a proximal flow sensor (PFS).

METHODS

IMV was simulated using a ventilator connected to a lung model through an 8-mm inner-diameter endotracheal tube. The impact of a decelerating and a constant flow pattern on aerosol delivery was evaluated in volume-controlled mode (tidal volume 500 mL, 20 breaths/min, inspiratory time of 1 sec, bias flow of 10 L/min). An amikacin solution (250 mg/3 mL) was nebulized with Aeroneb Solo(®) placed at five positions on the ventilator circuit equipped with a PFS: connected to the endotracheal tube (A), to the Y-piece (B), placed at 15 cm (C) and 45 cm upstream of the Y-piece (D), and placed at 15 cm of the inspiratory outlet of the ventilator (E). The four last positions were also tested without PFS. Deposited doses of amikacin were measured using the gravimetric residual method.

RESULTS

Amikacin delivery was significantly reduced with a decelerating inspiratory flow pattern compared to a constant flow (p<0.05). With a constant inspiratory flow pattern, connecting the nebulizer to the endotracheal tube enabled similar deposited doses than these obtained when connecting the nebulizer close to the ventilator. The PFS reduced deposited doses only when the nebulizer was connected to the Y-piece with both flow patterns or placed at 15 cm of the Y-piece with a constant inspiratory flow (p<0.01).

CONCLUSIONS

Using similar tidal volume and inspiratory time, a constant flow pattern (30 L/min) delivers a higher amount of amikacin through an endotracheal tube compared to a decelerating inspiratory flow pattern (peak inspiratory flow around 60 L/min). The optimal nebulizer position depends on the inspiratory flow pattern and the presence of a PFS.