Ventilation-perfusion mismatching in acute severe asthma: effects of salbutamol and 100% oxygen

Oxygen Saturation Sub-analyses Errors in the Dominant Meta-analysis Used to Deimplement Albuterol as a Therapeutic Option for Bronchiolitis

OBJECTIVE

Clinical experience and patient-level physiological studies indicate that albuterol transiently reduces oxygen saturation, irrespective of the underlying respiratory condition causing the wheezing. Three revisions of the Cochrane review, Bronchodilators for Bronchiolitis (Review), have found that albuterol temporarily increases oxygen saturation. Rarely, these findings were even statistically significant, but the direction of effect is consistently opposite from physiological studies. In this study, we attempted to resolve this apparent paradox.

METHODS

The original trial publications included in multiple oxygen saturation sub-analyses in the 2006, 2010, and 2014 updates of the Cochrane review were assessed for appropriate study inclusion, correctness of calculations, and correct analysis with respect to direction of effect. The studies were also reviewed to assess whether the data was correctly transferred to the meta-analysis software. We repeated the meta-analyses calculations after correcting for suspected errors and plotted the results of the meta-analyses as originally reported and in their corrected form on an albatross plot.

RESULTS

We found data miscalculations, errors of transposition of albuterol and placebo data, the inclusion of inpatient data in outpatient analyses, and questionable study inclusions in the 3 Cochrane review updates. After corrections were made, the direction of effect of albuterol switched negative, albeit nonsignificantly, a finding most consistent with clinical and physiological observations. In addition, the very wide heterogeneity between the original meta-analyses disappeared.

CONCLUSION

After multiple suspected data flaws were corrected our reanalyses of the reported data confirmed that decreased oxygen saturation can be expected following administration of albuterol to infants presenting with bronchiolitis syndrome, thereby resolving the apparent paradox in favor of clinical observation and research physiology.

Assessing the pulmonary vascular responsiveness to oxygen with proton MRI

Ventilation-perfusion matching occurs passively and is also actively regulated through hypoxic pulmonary vasoconstriction (HPV). The extent of HPV activity in humans, particularly normal subjects, is uncertain. Current evaluation of HPV assesses changes in ventilation-perfusion relationships/pulmonary vascular resistance with hypoxia and is invasive, or unsuitable for patients because of safety concerns. We used a noninvasive imaging-based approach to quantify the pulmonary vascular response to oxygen as a metric of HPV by measuring perfusion changes between breathing 21% and 30%O2 using arterial spin labeling (ASL) MRI. We hypothesized that the differences between 21% and 30%O2 images reflecting HPV release would be 1) significantly greater than the differences without [Formula: see text] changes (e.g., 21-21% and 30-30%O2) and 2) negatively associated with ventilation-perfusion mismatch. Perfusion was quantified in the right lung in normoxia (baseline), after 15 min of 30% O2 breathing (hyperoxia) and 15 min normoxic recovery (recovery) in healthy subjects (7 M, 7 F; age = 41.4 ± 19.6 yr). Normalized, smoothed, and registered pairs of perfusion images were subtracted and the mean square difference (MSD) was calculated. Separately, regional alveolar ventilation and perfusion were quantified from specific ventilation, proton density, and ASL imaging; the spatial variance of ventilation-perfusion (σ2V̇a/Q̇) distributions was calculated. The O2-responsive MSD was reproducible (R2 = 0.94, P < 0.0001) and greater (0.16 ± 0.06, P < 0.0001) than that from subtracted images collected under the same [Formula: see text] (baseline = 0.09 ± 0.04, hyperoxia = 0.08 ± 0.04, recovery = 0.08 ± 0.03), which were not different from one another (P = 0.2). The O2-responsive MSD was correlated with σ2V̇a/Q̇ (R2 = 0.47, P = 0.007). These data suggest that active HPV optimizes ventilation-perfusion matching in normal subjects. This noninvasive approach could be applied to patients with different disease phenotypes to assess HPV and ventilation-perfusion mismatch.NEW & NOTEWORTHY We developed a new proton MRI method to noninvasively quantify the pulmonary vascular response to oxygen. Using a hyperoxic stimulus to release HPV, we quantified the resulting redistribution of perfusion. The differences between normoxic and hyperoxic images were greater than those between images without [Formula: see text] changes and negatively correlated with ventilation-perfusion mismatch. This suggests that active HPV optimizes ventilation-perfusion matching in normal subjects. This approach is suitable for assessing patients with different disease phenotypes.

Pulmonary MRI with hyperpolarized xenon-129 demonstrates novel alterations in gas transfer across the air-blood barrier in asthma

BACKGROUND

Individuals with asthma can vary widely in clinical presentation, severity, and pathobiology. Hyperpolarized xenon-129 (Xe129) MRI is a novel imaging method to provide 3-D mapping of both ventilation and gas exchange in the human lung.

PURPOSE

To evaluate the functional changes in adults with asthma as compared to healthy controls using Xe129 MRI.

METHODS

All subjects (20 controls and 20 asthmatics) underwent lung function measurements and Xe129 MRI on the same day. Outcome measures included the pulmonary ventilation defect and transfer of inspired Xe129 into two soluble compartments: tissue and blood. Ten asthmatics underwent Xe129 MRI before and after bronchodilator to test whether gas transfer measures change with bronchodilator effects.

RESULTS

Initial analysis of the results revealed striking differences in gas transfer measures based on age, hence we compared outcomes in younger (n = 24, ≤ 35 years) versus older (n = 16, > 45 years) asthmatics and controls. The younger asthmatics exhibited significantly lower Xe129 gas uptake by lung tissue (Asthmatic: 0.98% ± 0.24%, Control: 1.17% ± 0.12%, P = 0.035), and higher Xe129 gas transfer from tissue to the blood (Asthmatic: 0.40 ± 0.10, Control: 0.31% ± 0.03%, P = 0.035) than the younger controls. No significant difference in Xe129 gas transfer was observed in the older group between asthmatics and controls (P > 0.05). No significant change in Xe129 transfer was observed before and after bronchodilator treatment.

CONCLUSIONS

By using Xe129 MRI, we discovered heterogeneous alterations of gas transfer that have associations with age. This finding suggests a heretofore unrecognized physiological derangement in the gas/tissue/blood interface in young adults with asthma that deserves further study.

Pulmonary functional MRI: Detecting the structure-function pathologies that drive asthma symptoms and quality of life

Pulmonary functional MRI (PfMRI) using inhaled hyperpolarized, radiation-free gases (such as ³ He and ¹²⁹ Xe) provides a way to directly visualize inhaled gas distribution and ventilation defects (or ventilation heterogeneity) in real time with high spatial (~mm³ ) resolution. Both gases enable quantitative measurement of terminal airway morphology, while ¹²⁹ Xe uniquely enables imaging the transfer of inhaled gas across the alveolar-capillary tissue barrier to the red blood cells. In patients with asthma, PfMRI abnormalities have been shown to reflect airway smooth muscle dysfunction, airway inflammation and remodelling, luminal occlusions and airway pruning. The method is rapid (8-15 s), cost-effective (~$300/scan) and very well tolerated in patients, even in those who are very young or very ill, because unlike computed tomography (CT), positron emission tomography and single-photon emission CT, there is no ionizing radiation and the examination takes only a few seconds. However, PfMRI is not without limitations, which include the requirement of complex image analysis, specialized equipment and additional training and quality control. We provide an overview of the three main applications of hyperpolarized noble gas MRI in asthma research including: (1) inhaled gas distribution or ventilation imaging, (2) alveolar microstructure and finally (3) gas transfer into the alveolar-capillary tissue space and from the tissue barrier into red blood cells in the pulmonary microvasculature. We highlight the evidence that supports a deeper understanding of the mechanisms of asthma worsening over time and the pathologies responsible for symptoms and disease control. We conclude with a summary of approaches that have the potential for integration into clinical workflows and that may be used to guide personalized treatment planning.

Effect of Salbutamol on Lung Ventilation in Children with Cystic Fibrosis: Comprehensive Assessment Using Spirometry, Multiple-Breath Washout, and Functional Lung Magnetic Resonance Imaging

BACKGROUND

Inhalation therapy is one of the cornerstones of the daily treatment regimen in patients with cystic fibrosis (CF). Recommendations regarding the addition of bronchodilators, especially salbutamol are conflicting due to the lack of evidence. New diagnostic measures such as multiple-breath washout (<underline>MBW)</underline> and functional magnetic resonance imaging (MRI) have the potential to reveal new insights into bronchodilator effects in patients with CF.

OBJECTIVE

The objective of the study was to comprehensively assess the functional response to nebulized inhalation with salbutamol in children with CF.

METHODS

Thirty children aged 6-18 years with stable CF performed pulmonary function tests, MBW, and matrix pencil-MRI before and after standardized nebulized inhalation of salbutamol.

RESULTS

Lung clearance index decreased (improved) by -0.24 turnover (95% confidence interval [CI]: -0.53 to 0.06; p = 0.111). Percentage of the lung volume with impaired fractional ventilation and relative perfusion decreased (improved) by -0.79% (CI: -1.99 to 0.42; p = 0.194) and -1.31% (CI: -2.28 to -0.35; p = 0.009), respectively. Forced expiratory volume (FEV1) increased (improved) by 0.41 z-score (CI: 0.24-0.58; p < 0.0001). We could not identify specific clinical factors associated with a more pronounced effect of salbutamol.

CONCLUSIONS

There is a positive short-term effect of bronchodilator inhalation on FEV1 in patients with CF, which is independent of ventilation inhomogeneity. Heterogeneous response between patients suggests that for prediction of a therapeutic effect this should be tested by spirometry in every patient individually.

Adhatoda vasica rescues the hypoxia-dependent severe asthma symptoms and mitochondrial dysfunction

Severe asthma is a chronic airway disease that exhibits poor response to conventional asthma therapies. Growing evidence suggests that elevated hypoxia increases the severity of asthmatic inflammation among patients and in model systems. In this study, we elucidate the therapeutic effects and mechanistic basis of Adhatoda vasica (AV) aqueous extract on mouse models of acute allergic as well as severe asthma subtypes at physiological, histopathological, and molecular levels. Oral administration of AV extract attenuates the increased airway resistance and inflammation in acute allergic asthmatic mice and alleviates the molecular signatures of steroid (dexamethasone) resistance like IL-17A, KC (murine IL-8 homologue), and HIF-1α (hypoxia-inducible factor-1α) in severe asthmatic mice. AV inhibits HIF-1α levels through restoration of expression of its negative regulator-PHD2 (prolyl hydroxylase domain-2). Alleviation of hypoxic response mediated by AV is further confirmed in the acute and severe asthma model. AV reverses cellular hypoxia-induced mitochondrial dysfunction in human bronchial epithelial cells-evident from bioenergetic profiles and morphological analysis of mitochondria. In silico docking of AV constituents reveal higher negative binding affinity for C and O-glycosides for HIF-1α, IL-6, Janus kinase 1/3, TNF-α, and TGF-β-key players of hypoxia inflammation. This study for the first time provides a molecular basis of action and effect of AV whole extract that is widely used in Ayurveda practice for diverse respiratory ailments. Further, through its effect on hypoxia-induced mitochondrial dysfunction, the study highlights its potential to treat severe steroid-resistant asthma.

Assessment of bronchial obstruction and its reversibility by shape indexes of the flow-volume loop in asthmatic children

Asthma assessment by spirometry is challenging in children as forced expiratory volume in 1 s (FEV1) is frequently normal at baseline. Bronchodilator (BD) reversibility testing may reinforce asthma diagnosis but FEV1 sensitivity in children is controversial. Ventilation inhomogeneity, an early sign of airway obstruction, is described by the upward concavity of the descending limb of the forced expiratory flow-volume loop (FVL), not detected by FEV1. The aim was to test the sensitivity and specificity of FVL shape indexes as β-angle and forced expiratory flow at 50% of the forced vital capacity (FEF50)/peak expiratory flow (PEF) ratio, to identify asthmatics from healthy children in comparison to "usual" spirometric parameters. Seventy-two school-aged asthmatic children and 29 controls were prospectively included. Children performed forced spirometry at baseline and after BD inhalation. Parameters were expressed at baseline as z-scores and BD reversibility as percentage of change reported to baseline value (Δ%). Receiver operating characteristic curves were generated and sensitivity and specificity at respective thresholds reported. Asthmatics presented significantly smaller zβ-angle, zFEF50/PEF and zFEV1 (p ≤ .04) and higher BD reversibility, significant for Δ%FEF50/PEF (p = .02) with no difference for Δ%FEV1. zβ-angle and zFEF50/PEF exhibited better sensitivity (0.58, respectively 0.60) than zFEV1 (0.50), and similar specificity (0.72). Δ%β-angle showed higher sensitivity compared to Δ%FEV1 (0.72 vs. 0.42), but low specificity (0.52 vs. 0.86). Quantitative and qualitative assessment of FVL by adding shape indexes to spirometry interpretation may improve the ability to detect an airway obstruction, FEV1 reflecting more proximal while shape indexes peripheral bronchial obstruction.

Effects of an allosteric hemoglobin affinity modulator on arterial blood gases and cardiopulmonary responses during normoxic and hypoxic low-intensity exercise

Numerous pathophysiological conditions induce hypoxemia-related cardiopulmonary perturbations, decrements in exercise capacity, and debilitating symptoms. Accordingly, this study investigated the efficacy of an allosteric hemoglobin modulator (voxelotor) to enhance arterial oxygen saturation during low-intensity exercise in hypoxia. Eight normal healthy subjects (36 ± 7 yr; 73.8 ± 9.5 kg; 3 women) completed a submaximal cycling test (60 W) under normoxic ([Formula: see text]: 0.21; O₂ partial pressure: 144 mmHg) and hypoxic ([Formula: see text]: 0.125; O₂ partial pressure: 82 mmHg) conditions before (day 1) and after (day 15) 14 days of oral drug administration. While stationary on a cycle ergometer and during exercise, ratings of perceived exertion (RPE) and dyspnea, oxygen consumption (V̇o₂), and cardiac output (Q) were measured noninvasively, while arterial blood pressure (MAP) and blood gases ([Formula: see text], [Formula: see text], and [Formula: see text]) were measured invasively. The 14-day drug administration left shifted the oxygen-hemoglobin dissociation curve (ODC; p50 measured at standard pH and Pco₂; day 1: 28.0 ± 2.1 mmHg vs. day 15: 26.1 ± 1.8 mmHg, P < 0.05). RPE, dyspnea, V̇o₂, Q, and MAP were not different between day 1 and day 15. [Formula: see text] was similar during normoxia on day 1 and day 15 while stationary but higher during exercise (day 1: 95.2 ± 0.4% vs. day 15: 96.6 ± 0.3%, P < 0.05). [Formula: see text] was higher during hypoxia on day 15 while stationary (day 1: 82.9 ± 3.4% vs. day 15: 90.9 ± 1.8%, P < 0.05) and during exercise (day 1: 73.6 ± 2.5% vs. day 15: 84.8 ± 2.7%, P < 0.01). [Formula: see text] and [Formula: see text]were systematically higher and lower, respectively, after drug (P < 0.01), while the alveolar-arterial oxygen difference was unchanged suggesting hyperventilation contributed to the rise in [Formula: see text]. Oral administration of voxelotor left shifted the ODC and stimulated a mild hyperventilation, leading to improved arterial oxygen saturation without altering V̇o₂ and central hemodynamics during rest and low-intensity exercise. This effect was more pronounced during submaximal hypoxic exercise, when arterial desaturation was more evident. Additional studies are needed to determine the effects of voxelotor during maximal exercise and under chronic forms of hypoxia.NEW & NOTEWORTHY In humans, a novel allosteric hemoglobin-oxygen affinity modulator was administered to comprehensively examine the cardiopulmonary consequences of stabilizing a portion of the available hemoglobin in a high-oxygen affinity state during submaximal exercise in normoxia and hypoxia. Oral administration of voxelotor enhanced arterial oxygen saturation during submaximal exercise without altering oxygen consumption and central hemodynamics; however, the partial pressure of arterial carbon dioxide was reduced and the partial pressure of arterial oxygen was increased implying that hyperventilation also contributed to the increase in oxygen saturation. The preservation of arterial oxygen saturation and content was particularly evident during hypoxic submaximal exercise, when arterial desaturation typically occurs, but this did not influence arterial-venous oxygen difference.

Randomized clinical trial of high concentration versus titrated oxygen use in pediatric asthma

OBJECTIVE

To compare the effects of high concentration to titrated oxygen therapy (HCOT) on transcutaneous carbon dioxide (PtCO₂ ) level in pediatric asthma exacerbation. Titrated oxygen therapy (TOT) in acute asthma will avoid a rise in PtCO ₂ in the pediatric population.

METHOD

The study design is a prospective, randomized, clinical trial comparing HCOT (maintain SpO2 92-95%) while being treated for asthma exacerbation in the emergency department (ED).

INCLUSION CRITERIA

2 to 18 years, previously diagnosed asthma with acute exacerbation (asthma score >5). PtCO₂ and asthma scores were measured at 0, 20, 40, 60 minutes and then every 30 minutes until disposition decision. The primary outcome was a change in PtCO ₂ . Secondary outcomes were admission rate and change in asthma score.

RESULTS

A total of 96 patients were enrolled in the study with a mean age of 8.27 years; 49 in HCOT and 47 in the TOT group. The 0 minute PtCO₂ was similar (35.33 + 3.88 HCOT vs 36.66 + 4.69 TOT, P = 0.13); whereas, the 60 minutes PtCO ₂ was higher in the HCOT (38.08 + 5.11 HCOT vs 35.51 + 4.57 TOT, P = 0.01). The asthma score was similar at 0 minute (7.55 + 1.34 HCOT vs 7.30 + 1.18 TOT, P = 0.33); whereas, the 60 minutes asthma score was lower in the TOT (4.71 + 1.38 HCOT vs 3.57 + 1.25 TOT, P = 0.0001). The rate of admission to the hospital was 40.5% in HCOT vs 25.5% in the TOT (P = 0.088).

CONCLUSIONS

HCOT in pediatric asthma exacerbation leads to significantly higher carbon dioxide levels, which increases asthma scores and trends towards the increasing rate of admission. Larger studies are needed to explore this association.

Repeated doses of salbutamol and aeroallergen sensitisation both increased salbutamol-induced hypoxia in children and adolescents with acute asthma

AIM

We aimed to identify the frequency, magnitude and risk factors of salbutamol-induced hypoxia in children with acute asthma.

METHODS

This study was conducted at Hacettepe University on children who presented to the paediatric allergy clinic or the paediatric emergency room with acute asthma between July 2014 and June 2015. Vital signs, pulse oximetry-defined oxygen saturation and modified pulmonary index scores were evaluated before and after the first, second and third doses of nebulised salbutamol and repeated one and 10 days later.

RESULTS

We included 304 patients (65.7% male) from median age of 5.3 years (range 1-18 years). Salbutamol-induced hypoxia was detected in 14.7%, 3.9% and 1.3%, respectively, after the first, second and third doses of salbutamol. The risk factors for hypoxia were younger age and a higher modified pulmonary index score, but the risk factors for salbutamol-induced hypoxia were the number of salbutamol doses given in the last six hours and the presence of aeroallergen sensitisation. The maximum decrease in oxygen saturation after salbutamol was %5.

CONCLUSION

Although bronchodilators are the first-line treatment for acute asthma, they caused modest hypoxaemia, especially at repeated doses and, or, in patients with aeroallergen sensitisation.

Hypoxic Pulmonary Vasoconstriction Does Not Explain All Regional Perfusion Redistribution in Asthma

RATIONALE

Regional hypoventilation in bronchoconstricted patients with asthma is spatially associated with reduced perfusion, which is proposed to result from hypoxic pulmonary vasoconstriction (HPV).

OBJECTIVES

To determine the role of HPV in the regional perfusion redistribution in bronchoconstricted patients with asthma.

METHODS

Eight patients with asthma completed positron emission tomographic/computed tomographic lung imaging at baseline and after bronchoconstriction, breathing either room air or 80% oxygen (80% O₂) on separate days. Relative perfusion, specific ventilation (sV), and gas fraction (Fgas) in the 25% of the lung with the lowest specific ventilation (sV_low) and the remaining lung (sV_high) were quantified and compared.

MEASUREMENTS AND MAIN RESULTS

In the sV_low region, bronchoconstriction caused a significant decrease in sV under both room air and 80% O₂ conditions (baseline vs. bronchoconstriction, mean ± SD, 1.02 ± 0.20 vs. 0.35 ± 0.19 and 1.03 ± 0.20 vs. 0.32 ± 0.16, respectively; P < 0.05). In the sV_low region, relative perfusion decreased after bronchoconstriction under room air conditions and also, to a lesser degree, under 80% O₂ conditions (1.02 ± 0.19 vs. 0.72 ± 0.08 [P < 0.001] and 1.08 ± 0.19 vs. 0.91 ± 0.12 [P < 0.05], respectively). The Fgas increased after bronchoconstriction under room air conditions only (0.99 ± 0.04 vs. 1.00 ± 0.02; P < 0.05). The sV_low subregion analysis indicated that some of the reduction in relative perfusion after bronchoconstriction under 80% O₂ conditions occurred as a result of the presence of regional hypoxia. However, relative perfusion was also significantly reduced in sV_low subregions that were hyperoxic under 80% O₂ conditions.

CONCLUSIONS

HPV is not the only mechanism that contributes to perfusion redistribution in bronchoconstricted patients with asthma, suggesting that another nonhypoxia mechanism also contributes. We propose that this nonhypoxia mechanism may be either direct mechanical interactions and/or unidentified intercellular signaling between constricted airways, the parenchyma, and the surrounding vasculature.

Mechanisms of hypoxemia

Oxygen is an essential element for life and without oxygen humans can survive for few minutes only. There should be a balance between oxygen demand and delivery in order to maintain homeostasis within the body. The two main organ systems responsible for oxygen delivery in the body and maintaining homeostasis are respiratory and cardiovascular system. Abnormal function of any of these two would lead to the development of hypoxemia and its detrimental consequences. There are various mechanisms of hypoxemia but ventilation/perfusion mismatch is the most common underlying mechanism of hypoxemia. The present review will focus on definition, various causes, mechanisms, and approach of hypoxemia in human.

Bronchoconstriction induced by inhaled methacholine delays desflurane uptake and elimination in a piglet model

Bronchoconstriction is a hallmark of asthma and impairs gas exchange. We hypothesized that pharmacokinetics of volatile anesthetics would be affected by bronchoconstriction. Ventilation/perfusion (VA/Q) ratios and pharmacokinetics of desflurane in both healthy state and during inhalational administration of methacholine (MCh) to double peak airway pressure were studied in a piglet model. In piglets, MCh administration by inhalation (100 μg/ml, n=6) increased respiratory resistance, impaired VA/Q distribution, increased shunt, and decreased paO2 in all animals. The uptake and elimination of desflurane in arterial blood was delayed by nebulization of MCh, as determined by Micropore Membrane Inlet Mass Spectrometry (wash-in time to P50, healthy vs. inhalation: 0.5 min vs. 1.1 min, to P90: 4.0 min vs. 14.8 min). Volatile elimination was accordingly delayed. Inhaled methacholine induced severe bronchoconstriction and marked inhomogeneous VA/Q distribution in pigs, which is similar to findings in human asthma exacerbation. Furthermore, MCh-induced bronchoconstriction delayed both uptake and elimination of desflurane. These findings might be considered when administering inhalational anesthesia to asthmatic patients.

Delivery of heliox with a semi-closed circuit during spontaneous breathing: a comparative economic theoretical study

BACKGROUND

Heliox is a mixture of oxygen and helium which reduces airway resistance in patients with airway obstruction. In clinical practice, patients breathing spontaneously receive heliox via an open circuit. Recently, a semi-closed circuit for heliox administration has been proposed which minimizes consumption of heliox and therefore cost of the heliox therapy; although, the semi-closed circuit is associated with additional costs. The aim of the study is to conduct an economical analysis comparing total cost of heliox therapy using an open versus a semi-closed circuit in spontaneously breathing patients with airway obstruction.

METHODS

Four different systems for heliox administration were analyzed: an open circuit and three alternatives of a semi-closed circuit involving a custom made semi-closed circuit and two standard anesthesia machines. Total costs of heliox therapy were calculated for all the systems. For calculation of gas consumption, the clinical procedures limiting continuous heliox therapy including the aerosol therapy, personal hygiene and nutrition were taken into account. A sensitivity analysis was conducted for main input variables that may influence the results of the study.

RESULTS

Price of gases consumed by a semi-closed system represents less than 20 % of price of gases when a standard open circuit is used. This represents a saving of approximately 540 EUR per patient. The initial cost of the custom-made semi-closed circuit recuperates after treatment of 18 patients. The corresponding number of patients is 32 when a low-cost anesthesia machine is initially acquired and rises to 69 when a highly advanced anesthesia machine is considered.

CONCLUSIONS

Heliox therapy in spontaneously breathing patients using a semi-closed circuit becomes more cost-effective compared to the open circuit, currently used in clinical practice, when applied in a sufficient number of cases. The impact of finding a cheaper way of heliox administration on the clinical practice needs to be ascertained.

Blood gas tensions in adult asthma: a systematic review and meta-regression analysis

OBJECTIVE

The last half-century has seen substantial changes in asthma treatment and care. We investigated whether arterial blood gas parameters in acute and non-acute asthma have changed historically.

METHODS

We performed a systematic search of the literature for studies reporting P(aO2) , P(aCO2) and forced expiratory volume in 1 s, percentage of predicted (FEV1%). For each of the blood gas parameters, meta-regression analyses examined its association with four background variables: the publication year, mean FEV1%, mean age and female fraction in the respective studies.

RESULTS

After screening, we included 43 articles comprising 61 datasets published between 1967 and 2013. In studies of habitual-state asthma, mean P(aO2) was positively associated with the publication year (p = 0.001) and negatively with mean age (p < 0.01). Mean P(aCO2) showed a positive association with publication year (p = 0.001) and a negative association with female fraction (p < 0.05). In acute asthma studies, blood gas levels were unassociated with publication year and mean age, mean P(aO2) was positively associated with FEV1% (p < 0.05) whereas mean P(aCO2) showed a negative association with FEV1% (p < 0.05) for studies with mean FEV1% <40. In neither acute nor habitual-state studies was mean arterial pH associated with any of the predictor variables.

CONCLUSIONS

In studies of habitual-state asthma, mean reported P(aO2) and P(aCO2) levels were found to have increased since 1967. In acute asthma studies, mean P(aO2) and P(aCO2) were associated with mean FEV1% but not with either publication year or patient age.

A review of the use of adjunctive therapies in severe acute asthma exacerbation in critically ill children

Asthma is a common and potentially life threatening childhood condition. Asthma involves not only chronic airway remodeling, but may also include frequent exacerbations resulting from bronchospasm, edema, and mucus production. In children with severe exacerbations, standard therapy with β2-agonists, anti-cholinergic agents, oxygen, and systemic steroids may fail to reverse the severe airflow obstruction and necessitate use of adjunctive therapies. These therapies include intravenous or inhaled magnesium, inhaled helium-oxygen mixtures, intravenous methylxanthines, intravenous β2-agonists, and intravenous ketamine. Rarely, these measures are not successful and following the initiation of invasive mechanical ventilation, inhaled anesthetics or extracorporeal life support may be required. In this review, we discuss the mechanisms and evidence for adjunctive therapies in the setting of severe acute asthma exacerbations in children.

Noninvasive ventilation in acute asthma

Noninvasive ventilation (NIV) has well-recognized benefits in acute exacerbation of chronic obstructive pulmonary disease and pulmonary edema. Its utilization in acute asthma, however, remains controversial. In this review, we describe the physiological basis to justify NIV use in acute asthma and contribute a critical appraisal of the available literature relating to this practice. A discussion of some of the more pertinent, clinically relevant practicalities is also provided. Original research articles were identified using the electronic PubMed database. Randomized controlled trials of NIV in the setting of acute asthma were selected. Retrospective observational studies were also included if they were considered to contribute to the literature review. The use of NIV in the acute asthma setting has been shown to be associated with improvements in important physiological variables including measures of airflow and respiratory rate, and lends support to further study in this field. Improvements in airflow may be a direct effect of applied positive airway pressure or an indirect effect secondary to better dispersal of aerosolized medication. Reductions observed in respiratory rate and dyspnea are likely influenced by the amount of pressure support provided. Evidence suggestive of any improvement in mortality, intubation rate, or hospital/intensive care unit length of stay, however, is lacking. Studies to date have been hampered by small numbers and a lack of demonstrable meaningful clinical outcomes. Data relating to mortality, endotracheal intubation rates, and hospital length of stay/admission should be sought in future large clinical trials.

Gas exchange in disease: asthma, chronic obstructive pulmonary disease, cystic fibrosis, and interstitial lung disease

Ventilation-perfusion (VA/Q) inequality is the underlying abnormality determining hypoxemia and hypercapnia in lung diseases. Hypoxemia in asthma is characterized by the presence of low VA/Q units, which persist despite improvement in airway function after an attack. This hypoxemia is generally attenuated by compensatory redistribution of blood flow mediated by hypoxic vasoconstriction and changes in cardiac output, however, mediator release and bronchodilator therapy may cause deterioration. Patients with chronic obstructive pulmonary disease have more complex patterns of VA/Q inequality, which appear more fixed, and changes in blood flow and ventilation have less benefit in improving gas exchange efficiency. The inability of ventilation to match increasing cardiac output limits exercise capacity as the disease progresses. Deteriorating hypoxemia during exacerbations reflects the falling mixed venous oxygen tension from increased respiratory muscle activity, which is not compensated by any redistribution of VA/Q ratios. Shunt is not a feature of any of these diseases. Patients with cystic fibrosis (CF) have no substantial shunt when managed according to modern treatment regimens. Interstitial lung diseases demonstrate impaired oxygen diffusion across the alveolar-capillary barrier, particularly during exercise, although VA/Q inequality still accounts for most of the gas exchange abnormality. Hypoxemia may limit exercise capacity in these diseases and in CF. Persistent hypercapnic respiratory failure is a feature of advancing chronic obstructive pulmonary disease and CF, closely associated with sleep disordered breathing, which is not a prominent feature of the other diseases. Better understanding of the mechanisms of hypercapnic respiratory failure, and of the detailed mechanisms controlling the distribution of ventilation and blood flow in the lung, are high priorities for future research.

Balancing the risks and benefits of oxygen therapy in critically III adults

Oxygen therapy is an integral part of the treatment of critically ill patients. Maintenance of adequate oxygen delivery to vital organs often requires the administration of supplemental oxygen, sometimes at high concentrations. Although oxygen therapy is lifesaving, it may be associated with deleterious effects when administered for prolonged periods at high concentrations. Here, we review the recent advances in our understanding of the molecular responses to hypoxia and high levels of oxygen and review the current guidelines for oxygen therapy in critically ill patients.

The effect of high concentration oxygen therapy on PaCO2 in acute and chronic respiratory disorders

There is evidence that the potential for high concentration oxygen therapy to increase PaCO₂ is not limited to stable and acute exacerbations of COPD, but also to other acute respiratory disorders with abnormal gas exchange such as asthma and pneumonia, and chronic respiratory conditions with hypercapnia such as obesity hypoventilation syndrome. This evidence forms the basis of consensus guidelines which recommend that oxygen therapy is titrated in COPD and other respiratory conditions, to ensure the maximal benefits of oxygen therapy are achieved while reducing the potential for harm due to hyperoxia.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

[Increased inspiratory oxygen fractions (FIO2) using a conventional drug delivery nebuliser]

Nebulised drugs are very useful in COPD exacerbations. The most frequently used propellant is compressed air, which is commonly administered together with nasal oxygen in those patients with respiratory failure. The purpose of this approach is to avoid the risks inherent in breathing high inspiratory oxygen fractions (FIO(2)).

AIM

To analyze the actual FIO(2) obtained with such a common method under experimental conditions.

METHODS

Volunteers breathed using different patterns (quiet breathing, panting and deep breathing), through either the nose or the mouth, with oxygen flows of 0 vs. 4l/min. Then, they repeated quiet breathing and panting patterns, with nebulization of saline propelled by compressed air (8l/min) and oxygen flows of 0, 2, 4, 6 and 8l/min. The F(I)O(2) was simultaneously determined both in retronasal (RN) and retropharyngeal (RF) areas.

RESULTS

During breathing without simultaneous nebulization and oxygen flow of 4l/min, FIO(2) reached mean values of 0.42-0.71 (RN) and 0.29-0.38 (RF) for the three ventilatory patterns analyzed. With nebulisations during quiet breathing, mean FIO(2) values were 0.39 (RN) and 0.27 (RF) for 2l/min O(2) flow, 0.47 (RN), 0.34 (RF) for 4l/min, 0.58 (RN), 0.38 (RF) for 6l/min, and 0.68 (RN) and 0.50 (RF) for 8l/min. Similar results were obtained with the panting pattern.

CONCLUSION

The FIO(2) obtained using the conventional nebulization system (propulsion with compressed air and simultaneous nasal oxygen therapy) are relatively high, and therefore, might involve risks for COPD patients during exacerbations.

Rapid intravenous infusion of 20 ml/kg saline does not impair resting pulmonary gas exchange in the healthy human lung

Rapid infusion of intravenous saline, a model of pulmonary interstitial edema, alters the distribution of pulmonary perfusion, raises pulmonary capillary blood volume, and increases bronchial wall thickness in humans. We hypothesized that infusion would disrupt pulmonary gas exchange by increasing ventilation/perfusion ((.)VA/(.)Q) inequality as opposed to a diffusive impairment in O2 exchange. Seven males (26 +/- 3 yr; FEV1: 110 +/- 16% predicted.) performed spirometry and had (.)VA/(.)Q mismatch measured using the multiple inert gas elimination technique, before and after 20 ml/kg iv of normal saline delivered in approximately 30 min. Infusion increased thoracic fluid content from transthoracic impedance by 12% (P < 0.0001) and left FVC unchanged but reduced expiratory flows (FEF(25-75) falling from 5.1 +/- 0.4 to 4.2 +/- 0.4 l/s, P < 0.05). However, (.)VA/(.)Q mismatch as measured by the log standard deviation of the ventilation (LogSD(.)V) and perfusion (LogSD(.)Q) distributions remained unchanged; LogSD(.)V: 0.40 +/- 0.03 pre, 0.38 +/- 0.04 post, NS; LogSD(.)Q: 0.38 +/- 0.03 pre, 0.37 +/- 0.03 post, NS. There was no significant change in arterial PO2 (99 +/- 2 pre, 99 +/- 3 mmHg post, NS) but arterial PCO2 was decreased (38.7 +/- 0.6 pre, 36.8 +/- 1.2 mmHg post, P < 0.05). Thus, infusion compressed small airways and caused a mild degree of hyperventilation. There was no evidence for a diffusive limitation to O2 exchange, with the measured-predicted alveolar-arterial oxygen partial pressure difference being unaltered by infusion at FIO2 = 0.125 (4.3 +/- 1.0 pre, 5.2 +/- 1.0 post, NS). After infusion, the fraction of perfusion going to areas with (.)VA/(.)Q < 1 was increased when a subject breathed a hyperoxic gas mixture [0.72 +/- 0.06 (FIO2 = 0.21), 0.80 +/- 0.06 (FIO2 = 0.30), P < 0.05] with similar effects on ventilation in the face of unchanged (.)VA and (.)Q. These results suggest active control of blood flow to regions of decreased ventilation during air breathing, thus minimizing the gas exchange consequences.

Ventilation-perfusion imbalance and chronic obstructive pulmonary disease staging severity

Chronic obstructive pulmonary disease (COPD) is characterized by a decline in forced expiratory volume in 1 s (FEV(1)) and, in many advanced patients, by arterial hypoxemia with or without hypercapnia. Spirometric and gas exchange abnormalities have not been found to relate closely, but this may reflect a narrow range of severity in patients studied. Therefore, we assessed the relationship between pulmonary gas exchange and airflow limitation in patients with COPD across the severity spectrum. Ventilation-perfusion (V(A)/Q) mismatch was measured using the multiple inert gas elimination technique in 150 patients from previous studies. The distribution of patients according to the GOLD stage of COPD was: 15 with stage 1; 40 with stage 2; 32 with stage 3; and 63 with stage 4. In GOLD stage 1, AaPo(2) and V(A)/Q mismatch were clearly abnormal; thereafter, hypoxemia, AaPo(2), and V(A)/Q imbalance increased, but the changes from GOLD stages 1-4 were modest. Postbronchodilator FEV(1) was related to Pa(O(2)) (r = 0.62) and Pa(CO(2)) (r = -0.59) and to overall V(A)/Q heterogeneity (r = -0.48) (P < 0.001 each). Pulmonary gas exchange abnormalities in COPD are related to FEV(1) across the spectrum of severity. V(A)/Q imbalance, predominantly perfusion heterogeneity, is disproportionately greater than airflow limitation in GOLD stage 1, suggesting that COPD initially involves the smallest airways, parenchyma, and pulmonary vessels with minimal spirometric disturbances. That progression of V(A)/Q inequality with spirometric severity is modest may reflect pathogenic processes that reduce both local ventilation and blood flow in the same regions through airway and alveolar disease and capillary involvement.

Acute severe asthma: new approaches to assessment and treatment

The precise definition of a severe asthmatic exacerbation is an issue that presents difficulties. The term 'status asthmaticus' relates severity to outcome and has been used to define a severe asthmatic exacerbation that does not respond to and/or perilously delays the repetitive or continuous administration of short-acting inhaled beta(2)-adrenergic receptor agonists (SABA) in the emergency setting. However, a number of limitations exist concerning the quantification of unresponsiveness. Therefore, the term 'acute severe asthma' is widely used, relating severity mostly to a combination of the presenting signs and symptoms and the severity of the cardiorespiratory abnormalities observed, although it is well known that presentation does not foretell outcome. In an acute severe asthma episode, close observation plus aggressive administration of bronchodilators (SABAs plus ipratropium bromide via a nebulizer driven by oxygen) and oral or intravenous corticosteroids are necessary to arrest the progression to severe hypercapnic respiratory failure leading to a decrease in consciousness that requires intensive care unit (ICU) admission and, eventually, ventilatory support. Adjunctive therapies (intravenous magnesium sulfate and/or others) should be considered in order to avoid intubation. Management after admission to the hospital ward because of an incomplete response is similar. The decision to intubate is essentially based on clinical judgement. Although cardiac or respiratory arrest represents an absolute indication for intubation, the usual picture is that of a conscious patient struggling to breathe. Factors associated with the increased likelihood of intubation include exhaustion and fatigue despite maximal therapy, deteriorating mental status, refractory hypoxaemia, increasing hypercapnia, haemodynamic instability and impending coma or apnoea. To intubate, sedation is indicated in order to improve comfort, safety and patient-ventilator synchrony, while at the same time decrease oxygen consumption and carbon dioxide production. Benzodiazepines can be safely used for sedation of the asthmatic patient, but time to awakening after discontinuation is prolonged and difficult to predict. The most common alternative is propofol, which is attractive in patients with sudden-onset (near-fatal) asthma who may be eligible for extubation within a few hours, because it can be titrated rapidly to a deep sedation level and has rapid reversal after discontinuation; in addition, it possesses bronchodilatory properties. The addition of an opioid (fentanyl or remifentanil) administered by continuous infusion to benzodiazepines or propofol is often desirable in order to provide amnesia, sedation, analgesia and respiratory drive suppression. Acute severe asthma is characterized by severe pulmonary hyperinflation due to marked limitation of the expiratory flow. Therefore, the main objective of the initial ventilator management is 2-fold: to ensure adequate gas exchange and to prevent further hyperinflation and ventilator-associated lung injury. This may require hypoventilation of the patient and higher arterial carbon dioxide (PaCO(2)) levels and a more acidic pH. This does not apply to asthmatic patients intubated for cardiac or respiratory arrest. In this setting the post-anoxic brain oedema might demand more careful management of PaCO(2) levels to prevent further elevation of intracranial pressure and subsequent complications. Monitoring lung mechanics is of paramount importance for the safe ventilation of patients with status asthmaticus. The first line of specific pharmacological therapy in ventilated asthmatic patients remains bronchodilation with a SABA, typically salbutamol (albuterol). Administration techniques include nebulizers or metered-dose inhalers with spacers. Systemic corticosteroids are critical components of therapy and should be administered to all ventilated patients, although the dose of systemic corticosteroids in mechanically ventilated asthmatic patients remains controversial. Anticholinergics, inhaled corticosteroids, leukotriene receptor antagonists and methylxanthines offer little benefit, and clinical data favouring their use are lacking. In conclusion, expertise, perseverance, judicious decisions and practice of evidence-based medicine are of paramount importance for successful outcomes for patients with acute severe asthma.

Gas exchange response to short-acting beta2-agonists in chronic obstructive pulmonary disease severe exacerbations

RATIONALE

Short-acting beta(2)-agonists are one of the mainstays of bronchodilator strategy for exacerbations of chronic obstructive pulmonary disease (COPD). The assessment of pulmonary gas exchange after salbutamol in COPD severe exacerbations remains unknown.

OBJECTIVES

We investigated whether the effects of nebulized salbutamol during COPD severe exacerbations are associated with further deterioration of pulmonary gas exchange.

METHODS

We examined patients with severe COPD when hospitalized for exacerbation (n = 9), and while in stable convalescence.

MEASUREMENTS AND MAIN RESULTS

We assessed spirometry, arterial blood gases, systemic hemodynamics, and V/Q relationships 30 and 90 minutes after administration of 5.0 mg salbutamol. At exacerbation, compared with baseline, 30 minutes after salbutamol administration, cardiac output (Q) increased (from 6.5 +/- [SEM] 0.4 to 7.3 +/- 0.5 L . min(-1)) (p < 0.03) alone, without inducing changes in gas exchange indices. When in convalescence, compared with baseline, 30 minutes after salbutamol, there was an increase in Q (from 5.7 +/- 0.5 to 7.0 +/- 0.6 L . min(-1)) and Vo(2) (from 211 +/- 12 to 232 +/- 11 ml . min(-1)) (p < 0.002 each), whereas Pa(O(2)) decreased (from 71 +/- 4 to 63 +/- 3 mm Hg) and alveolar-arterial Po(2) difference increased due to increased perfusion of low-V/Q-ratio regions (from 4.5 +/- 2.6 to 9.6 +/- 4.1% of Q) (p < 0.05); Sa(O(2)) (93 +/- 2%) and Pa(CO(2)) (43 +/- 2 mm Hg) remained unchanged. This deleterious gas exchange response persisted at 90 minutes.

CONCLUSIONS

At exacerbation, salbutamol does not aggravate pulmonary gas exchange abnormalities. When in convalescence, however, baseline lung function improvement was associated with a detrimental gas exchange response to salbutamol, resulting in further V/Q imbalance and small decreases in Pa(O(2)) compounded by small increases in Q and Vo(2).

Effects of rac-albuterol on arterial blood gases in patients with stable hypercapnic chronic obstructive pulmonary disease

AIMS

Many patients with chronic obstructive pulmonary disease (COPD) are treated with high dose beta(2)-adrenoceptor agonists, which can increase ventilation/perfusion mismatching, and tremor and cardiac output, thereby increasing oxygen uptake and carbon dioxide output (VCO(2)). Patients with severe COPD and hypercapnia may be unable to increase ventilation in response to increased VCO(2), in which case arterial carbon dioxide tension (P(a)CO(2)) may rise. Our aim was to determine whether high dose nebulized rac-albuterol could increase P(a)CO(2) in patients with COPD, limited bronchodilator reversibilty and hypercapnia.

METHODS

We compared 10 mg and 400 microg rac-albuterol, given in two doses 1 h apart on nonconsecutive days, in a double-blind randomized crossover study in 14 patients with severe COPD. P(a)CO(2), arterial oxygen tension (P(a)O(2)) and heart rate were measured over 120 min and change from baseline was plotted against time to obtain an area under the curve.

RESULTS

Mean P(a)CO(2) fell slightly over 120 min, with no difference between treatments (0.03 kPa h(-1) (95% confidence interval 0.02, 0.04)) and only three subjects had an increase in P(a)CO(2) after high dose rac-albuterol. High dose rac-albuterol caused a greater fall in P(a)O(2)[0.1 kPa h(-1) (95% confidence interval 0, 0.2)] and increase in heart rate than the low dose, although the differences were small.

CONCLUSIONS

Under stable conditions most subjects with severe COPD and hypercapnia will have a fall in P(a)CO(2) and P(a)O(2) following 10 mg rac-albuterol, suggesting that they maintain capacity to respond to any increase in VCO(2) and prevent a rise in P(a)CO(2).

Comparison between nebulized adrenaline and beta2 agonists for the treatment of acute asthma. A meta-analysis of randomized trials

OBJECTIVE

To evaluate the efficacy of aerosolized adrenaline compared to inhaled beta(2) agonists in the treatment of acute asthma in the emergency setting.

DATA SOURCES

MEDLINE, EMBASE, CINAHI, and Cochrane databases, review articles, and references of included trials.

REVIEW METHODS

Published (1966-2005) randomized controlled trials with pulmonary function as primary outcome.

RESULTS

Six studies met the criteria for inclusion in the meta-analysis. They included 161 adults and 121 children and adolescents. Patients who received inhaled adrenaline showed a nonsignificant improvement in pulmonary function (standardized mean difference = 0.20, 95% confidence interval -0.22 to 0.63, P = .35) compared to patients getting inhaled beta(2) agonists. Moderate heterogeneity was identified between studies (I(2) = 47.2%). Homogeneity was achieved when studies that reported pulmonary function were stratified by intensity of adrenaline treatment. The use of more than 2 mg of adrenaline per dose was equivalent to 5 mg of salbutamol or terbutaline per dose. On the contrary, 2 mg or less of adrenaline per dose was inferior to 2.5 or 5 mg of salbutamol per dose. In addition, there were no differences in heart rate and Pao(2) between treatments.

CONCLUSIONS

There was no statistically significant benefit of nebulized adrenaline over salbutamol or terbutaline in the treatment of children and adults with moderate-severe acute asthma.

Blood gas analysis and chest x-ray findings in infants and preschool children with acute airway obstruction

BACKGROUND

The importance of SaO2 in the assessment of respiratory distress in bronchial asthma has been reported.

OBJECTIVES

To evaluate the correlation between blood gas analysis and chest X-ray lung opacities in young children presenting with acute respiratory symptoms.

METHODS

Eighty patients (43 males and 37 females aged 0.5-24 months; mean+/-SD 9.1+/-7.2 months), either with acute wheezing respiratory symptoms and/or with crackles were enrolled in our study. In all children, blood gas analysis and chest X-rays were performed within 12 h following admission to the emergency department.

RESULTS

In 55 children (68.75%) chest X-rays demonstrated lung opacities. Subjects with normal X-rays had paO2 and SaO2 higher than subjects with lung opacities (p<0.0001 and p=0.0001, respectively). Children with lung opacities almost always presented paO2<80 mm Hg. Sensitivity and specificity for the presence of lung opacities of paO2<80 mm Hg were 81 and 90%, respectively, while sensitivity and specificity of SaO2<95% were 92 and 40%, respectively. paO2<80 mm Hg in association with SaO2<95% had a positive predictive value for the diagnosis of pneumonia of 90.9%.

CONCLUSIONS

Our study suggests that blood gas analysis, particularly paO2, may help in predicting the presence of lung opacities in patients aged less than 2 years. However, chest X-rays may still be needed to define the actual extension of opacities as well as the possible concomitant presence of complications.

Theophylline versus terbutaline in treating critically ill children with status asthmaticus: a prospective, randomized, controlled trial

OBJECTIVE

To compare the efficacy of theophylline, terbutaline, or theophylline combined with terbutaline treatment in critically ill children with status asthmaticus who are already receiving continuous nebulized albuterol and intravenous corticosteroids.

DESIGN

Randomized, prospective, controlled, double-blind trial.

SETTING

Pediatric intensive care unit of a tertiary-care children's medical center.

PATIENTS

Forty critically ill children between the ages of 3 and 15 yrs with impending respiratory failure secondary to status asthmaticus.

INTERVENTIONS

All patients received intravenous methylprednisolone and continuous nebulized albuterol. The three study groups received theophylline plus placebo (group 1), terbutaline plus placebo (group 2), or theophylline and terbutaline together (group 3).

MEASUREMENTS AND MAIN RESULTS

Differences in baseline characteristics, change in clinical asthma score over time, length of pediatric intensive care unit stay, and incidence of adverse events were determined. The three study groups were similar in age, gender, race, asthma severity, and treatment. There were no differences in clinical asthma score over time, length of pediatric intensive care unit stay, or incidence of adverse events between the three groups, with the exception of a higher incidence of nausea in children in group 3. The median hospital cost of medication and theophylline blood levels was significantly lower in group 1 compared with groups 2 and 3 (280 US dollars vs. 3,908 US dollars vs. 4,045 US dollars, respectively, p < .0001).

CONCLUSIONS

Theophylline, when added to continuous nebulized albuterol therapy and intravenous corticosteroids, is as effective as terbutaline in treating critically ill children with status asthmaticus. The addition of theophylline to baseline therapy is more cost-effective when compared with terbutaline alone or terbutaline and theophylline together. Theophylline should be considered for use early in the management of critically ill asthmatic children.

The reversibility of increased airways resistance in chronic heart failure measured by impulse oscillometry

BACKGROUND

Patients with chronic heart failure complain of breathlessness and fatigue on exercise. Airways resistance is increased and lung compliance is reduced in chronic heart failure patients. The aim of this study was to determine whether the pulmonary abnormalities are reversible and whether any improvements lead to changes to exercise capacity or symptoms.

METHODS

Twelve patients with stable chronic heart failure and 10 matched controls underwent repeated assessment of airways resistance using impulse oscillometry and peak exercise testing with metabolic gas exchange after receiving nebulized saline as placebo or combined salbutamol and ipratropium bromide in a double-blind crossover randomized fashion.

RESULTS

Patients had lower peak oxygen consumption and a steeper slope relating ventilation to carbon dioxide production than controls. Bronchodilators reduced peripheral airways resistance in patients (0.53 versus 0.38, P<.02) and controls (0.21 versus 0.19, P<.005) and increased measures of compliance in both groups. There was no effect on the peak oxygen consumption, exercise time, ventilation to carbon dioxide slope, or anaerobic threshold. There was an increase in peak tidal volume (VT) in both groups but this did not lead to an increase in peak ventilation. The slope relating symptoms to ventilation (ie, Borg/VE) was significantly reduced in the patients after bronchodilators (17%+/-8%, P<.05). The relationship between the improvement in VT and reduction in gradient of the Borg/VE slope was significant (r=.40, P<.05).

CONCLUSIONS

Nebulized bronchodilators improve airways resistance, lung reactance, and peak tidal volume during exercise in chronic heart failure but do not increase peak exercise capacity. They do, however, reduce the symptom of breathlessness.

Comparison of nebulized epinephrine and terbutaline in patients with acute severe asthma: a controlled trial

PURPOSE

To compare the efficacy and tolerability of nebulized adrenaline and terbutaline in acute severe asthma.

METHODS

DESIGN

Prospective pilot randomized double-blind cross-over trial.

SETTING

Emergency department of a university hospital.

PATIENTS

Thirty-eight patients admitted with severe acute asthma. Each patient received adrenaline (3 mg) and terbutaline (5 mg) nebulizations over 20 min in randomized order. Additional treatment comprised methylprednisolone, intravenous hydration, and oxygen. The efficacy and tolerability of the two drugs were evaluated at the end of each nebulization as well as potential synergistic effects.

RESULTS

Eighteen patients received adrenaline first, and 20 received terbutaline first. Peak expiratory flow (PEF) improved significantly in both groups after the first nebulization (from 157 L/min +/- 111 L/min to 199 L/min +/- 134 L/min with adrenaline, P <.01; and from 142 L/min +/- 65 L/min to 193 L/min +/- 181 L/min with terbutaline, P <.01). Both drugs induced a significant decrease in respiratory frequency. The improvement in PaO2 was only significant with terbutaline. Respiratory frequency, PEF and PaO2 were not improved by the second nebulization. No adverse effects were observed.

CONCLUSIONS

Adrenaline nebulization was as effective and as well tolerated as terbutaline in acute severe asthma. No synergistic effect between terbutaline and adrenaline was observed.

Acute asthma in adults: a review

All patients with asthma are at risk of having exacerbations. Hospitalizations and emergency department (ED) visits account for a large proportion of the health-care cost burden of asthma, and avoidance or proper management of acute asthma (AA) episodes represent an area with the potential for large reductions in health-care costs. The severity of exacerbations may range from mild to life threatening, and mortality is most often associated with failure to appreciate the severity of the exacerbation, resulting in inadequate emergency treatment and delay in referring to hospital. This review describes the epidemiology, costs, pathophysiology, mortality, and management of adult AA in the ED and in the ICU.

Effects of short-term 28% and 100% oxygen on PaCO2 and peak expiratory flow rate in acute asthma: a randomized trial

STUDY OBJECTIVE

We conducted the first randomized controlled study to assess the effects of short-term 28% and 100% oxygen on PaCO(2) and peak expiratory flow rate (PEFR) in patients with acute severe asthma.

PATIENTS AND INTERVENTIONS

Seventy-four patients (mean age, 37.9 +/- 9.7 years [+/- SD]; PEFR, 41.0 +/- 12.1% of predicted) from two emergency departments were randomized to receive 28% or 100% oxygen during 20 min.

RESULTS

The administration of 100% oxygen significantly increases PaCO(2) (p = 0.03) and decreases PEFR (p = 0.001) as compared with administration of 28% oxygen. PaCO(2) before and during oxygen administration correlated significantly (p = 0.001) in both groups. Patients breathing 28% oxygen experienced a PaCO(2) fall; on the contrary, patients who received 100% oxygen showed an increase in PaCO(2), particularly those with PaCO(2) before oxygen treatment > 40 mm Hg.

CONCLUSIONS

This study confirmed previous observations that oxygen dose should be variable and based on achieving and maintaining target arterial oxygen saturation measured by pulse oximetry > or = 92% rather than on prescribing predetermined concentrations or flow rates of inspired oxygen.

Effects of montelukast on physical performance and exercise economy in adult asthmatics with exercise-induced bronchoconstriction

Leukotriene antagonists are effective in the treatment of exercise-induced bronchoconstriction. Montelukast is a specific cysteinyl-leukotriene receptor1 antagonist without known effects on the pulmonary vessels, which in theory should be advantageous with respect to gas exchange. In addition to lung function, we investigated the effects of montelukast on parameters of gas exchange and physical performance in 16 asthmatics with exercise-induced bronchoconstriction in a double-blind cross-over placebo-controlled study. Subjects were tested at an ambient temperature of -15 degrees C with a tread mill exercise protocol consisting of consecutive workloads of 80% V'O(2max) (6 min), rest (4 min), 60% V'O(2max) (6 min) and step increments of exercise until exhaustion. Montelukast reduced the maximum post-exercise fall in FEV1 (P < 0.01), improved the running time to exhaustion in 11 of 16 test subjects (one unchanged) (P = 0.03), and reduced the Borg score at exhaustion (P = 0.03) and the breathing frequency after 3 min at 60% V'O(2max) (P = 0.03). V'(O2), V'CO(2), minute ventilation, ventilatory equivalents, respiratory exchange ratio, heart rate and oxygen pulse were not significantly different after montelukast and placebo. We conclude that montelukast has a beneficial effect on physical performance in most adults with exercise-induced asthma without any observed effect on gas-exchange parameters.

Pharmacologic treatment of the adult hospitalized asthma patient

Acute severe asthma calls for aggressive and early therapy of a multifaceted and all-inclusive approach (Fig. 2). Therapy merely begins in the ED and manifold distinct issues need to find consideration during ongoing hospital care. Currently, beta-agonists, anti-cholinergic agents, and corticosteroids remain the mainstay of therapy. Methylxanthines and magnesium may find consideration in carefully selected patients. Multiple new therapeutic avenues, such as the anti-leukotriene drugs, seem promising and future studies will hopefully extend our armamentarium against life threatening complication of a common disease. Asthma education begun in the hospital may provide the platform for preventing severe acute exacerbations and hospitalization.

Acute asthma

OBJECTIVE: Asthma is the most common medical emergency in children. It is associated with significant morbidity and mortality rates and poses a tremendous societal burden worldwide. Management of the acute attack involves a stepwise approach that includes beta-agonist and steroid therapy, the mainstay of emergency treatment. Most patients will respond to this regime and can be discharged from the emergency department. Failure to respond to treatment necessitates hospital admission and sometimes admission to the intensive care unit (ICU). Management in the ICU involves intensification of pharmacologic therapy, including nonstandard therapies, in an attempt to avoid intubation and ventilation. When needed, mechanical ventilatory support can be rendered fairly safe with little morbidity if the likely cardiorespiratory physiologic derangements are appreciated and if appropriate ventilatory strategies are used. In the past two decades, the availability of newer potent medications and changes in approach to monitoring and ventilatory strategies have resulted in a decrease in ICU morbidity and mortality rates. Research endeavors are presently underway to further characterize the underlying mechanisms of the disease and are likely to lead to novel therapies. This article reviews the approach to management of acute severe asthma.