Clinical features and outcome in patients with acute asthma presenting with hypercapnia

German S3 Guideline: Oxygen Therapy in the Acute Care of Adult Patients

BACKGROUND

Oxygen (O2) is a drug with specific biochemical and physiological properties, a range of effective doses and may have side effects. In 2015, 14% of over 55,000 hospital patients in the UK were using oxygen. 42% of patients received this supplemental oxygen without a valid prescription. Health care professionals are frequently uncertain about the relevance of hypoxemia and have low awareness about the risks of hyperoxemia. Numerous randomized controlled trials about targets of oxygen therapy have been published in recent years. A national guideline is urgently needed.

METHODS

A national S3 guideline was developed and published within the Program for National Disease Management Guidelines (AWMF) with participation of 10 medical associations. A literature search was performed until February 1, 2021, to answer 10 key questions. The Oxford Centre for Evidence-Based Medicine (CEBM) System ("The Oxford 2011 Levels of Evidence") was used to classify types of studies in terms of validity. Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was used for assessing the quality of evidence and for grading guideline recommendation, and a formal consensus-building process was performed.

RESULTS

The guideline includes 34 evidence-based recommendations about indications, prescription, monitoring and discontinuation of oxygen therapy in acute care. The main indication for O2 therapy is hypoxemia. In acute care both hypoxemia and hyperoxemia should be avoided. Hyperoxemia also seems to be associated with increased mortality, especially in patients with hypercapnia. The guideline provides recommended target oxygen saturation for acute medicine without differentiating between diagnoses. Target ranges for oxygen saturation are based depending on ventilation status risk for hypercapnia. The guideline provides an overview of available oxygen delivery systems and includes recommendations for their selection based on patient safety and comfort.

CONCLUSION

This is the first national guideline on the use of oxygen in acute care. It addresses health care professionals using oxygen in acute out-of-hospital and in-hospital settings.

[German S3 Guideline - Oxygen Therapy in the Acute Care of Adult Patients]

BACKGROUND

 Oxygen (O₂) is a drug with specific biochemical and physiologic properties, a range of effective doses and may have side effects. In 2015, 14 % of over 55 000 hospital patients in the UK were using oxygen. 42 % of patients received this supplemental oxygen without a valid prescription. Healthcare professionals are frequently uncertain about the relevance of hypoxemia and have low awareness about the risks of hyperoxemia. Numerous randomized controlled trials about targets of oxygen therapy have been published in recent years. A national guideline is urgently needed.

METHODS

 A S3-guideline was developed and published within the Program for National Disease Management Guidelines (AWMF) with participation of 10 medical associations. Literature search was performed until Feb 1st 2021 to answer 10 key questions. The Oxford Centre for Evidence-Based Medicine (CEBM) System ("The Oxford 2011 Levels of Evidence") was used to classify types of studies in terms of validity. Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was used and for assessing the quality of evidence and for grading guideline recommendation and a formal consensus-building process was performed.

RESULTS

 The guideline includes 34 evidence-based recommendations about indications, prescription, monitoring and discontinuation of oxygen therapy in acute care. The main indication for O₂ therapy is hypoxemia. In acute care both hypoxemia and hyperoxemia should be avoided. Hyperoxemia also seems to be associated with increased mortality, especially in patients with hypercapnia. The guideline provides recommended target oxygen saturation for acute medicine without differentiating between diagnoses. Target ranges for oxygen saturation are depending on ventilation status risk for hypercapnia. The guideline provides an overview of available oxygen delivery systems and includes recommendations for their selection based on patient safety and comfort.

CONCLUSION

 This is the first national guideline on the use of oxygen in acute care. It addresses healthcare professionals using oxygen in acute out-of-hospital and in-hospital settings. The guideline will be valid for 3 years until June 30, 2024.

Elevated CO2 modulates airway contractility

Carbon dioxide (CO₂), a primary product of oxidative metabolism, can be sensed by eukaryotic cells eliciting unique responses via specific signalling pathways. Severe lung diseases such as chronic obstructive pulmonary disease are associated with hypoventilation that can lead to the elevation of CO₂ levels in lung tissues and the bloodstream (hypercapnia). However, the pathophysiological effects of hypercapnia on the lungs and specific lung cells are incompletely understood. We have recently reported using combined unbiased molecular approaches with studies in mice and cell culture systems on the mechanisms by which hypercapnia alters airway smooth muscle contractility. In this review, we provide a pathophysiological and mechanistic perspective on the effects of hypercapnia on the lung airways and discuss the recent understanding of high CO₂ modulation of the airway contractility.

Hypercapnia: An Aggravating Factor in Asthma

Asthma is a common chronic respiratory disorder with relatively good outcomes in the majority of patients with appropriate maintenance therapy. However, in a small minority, patients can experience severe asthma with respiratory failure and hypercapnia, necessitating intensive care unit admission. Hypercapnia occurs due to alveolar hypoventilation and insufficient removal of carbon dioxide (CO₂) from the blood. Although mild hypercapnia is generally well tolerated in patients with asthma, there is accumulating evidence that elevated levels of CO₂ can act as a gaso-signaling molecule, triggering deleterious effects in various organs such as the lung, skeletal muscles and the innate immune system. Here, we review recent advances on pathophysiological response to hypercapnia and discuss potential detrimental effects of hypercapnia in patients with asthma.

Acid-Base Disturbances in Patients with Asthma: A Literature Review and Comments on Their Pathophysiology

Asthma is a common illness throughout the world that affects the respiratory system function, i.e., a system whose operational adequacy determines the respiratory gases exchange. It is therefore expected that acute severe asthma will be associated with respiratory acid-base disorders. In addition, the resulting hypoxemia along with the circulatory compromise due to heart–lung interactions can reduce tissue oxygenation, with a particular impact on respiratory muscles that have increased energy needs due to the increased workload. Thus, anaerobic metabolism may ensue, leading to lactic acidosis. Additionally, chronic hypocapnia in asthma can cause a compensatory drop in plasma bicarbonate concentration, resulting in non-anion gap acidosis. Indeed, studies have shown that in acute severe asthma, metabolic acid-base disorders may occur, i.e., high anion gap or non-anion gap metabolic acidosis. This review briefly presents studies that have investigated acid-base disorders in asthma, with comments on their underlying pathophysiology.

Noninvasive Positive Pressure Ventilation for Acute Respiratory Failure in Emergency Department: a Qualitative Review

The roles of noninvasive positive pressure ventilation (NIPPV) as a treatment modality for patients presenting with acute respiratory failure (ARF) to the emergency department (ED) have not been clearly identified. The major advantages of NIPPV are avoiding patient's discomforts and complications relating to endotracheal intubation and mechanical ventilation. This review is to explore the current evidence on the effectiveness of NIPPV in various subgroups of patients with ARF. The rationales, advantages, complications and contraindications in the usage of NIPPV will also be discussed. There is robust evidence to support the use of NIPPV in severe acute exacerbation of chronic obstructive airway disease (COAD). A modest amount of favourable evidence supports the use of Continuous Positive Airway Pressure (CPAP) in cardiogenic pulmonary oedema, although the potential for harm has not been excluded. There exists no solid evidence supporting the use of NIPPV in asthma and pneumonia. Early institution of NIPPV in the ED is appropriate, feasible, likely to be beneficial and without major complications. Further good quality studies to evaluate the roles of NIPPV for ARF in the ED setting are needed to define which groups of patients can gain most benefit from this type of treatment.

Acute severe asthma

Preview How can the severity of an acute episode of asthma be assessed? What is a reasonable approach to corticosteroid administration in acute severe asthma? For which patients should mechanical ventilation be considered? The answers to these and other questions can be found in this guide to the evaluation and management of potentially fatal exacerbations of asthma.

Prognostic nomogram for inpatients with asthma exacerbation

Background

Asthma exacerbation may require a visit to the emergency room as well as hospitalization and can occasionally be fatal. However, there is limited information about the prognostic factors for asthma exacerbation requiring hospitalization, and no methods are available to predict an inpatient’s prognosis. We investigated the clinical features and factors affecting in-hospital mortality of patients with asthma exacerbation and generated a nomogram to predict in-hospital death using a national inpatient database in Japan.

Methods

We retrospectively collected data concerning hospitalization of adult patients with asthma exacerbation between July 2010 and March 2013 using the Japanese Diagnosis Procedure Combination database. We recorded patient characteristics and performed Cox proportional hazards regression analysis to assess the factors associated with all-cause in-hospital mortality. Then, we constructed a nomogram to predict in-hospital death.

Results

A total of 19,684 patients with asthma exacerbation were identified; their mean age was 58.8 years (standard deviation, 19.7 years) and median length of hospital stay was 8 days (interquartile range, 5–12 days). Among study patients, 118 died in the hospital (0.6%). Factors associated with higher in-hospital mortality included older age, male sex, reduced level of consciousness, pneumonia, and heart failure. A nomogram was generated to predict the in-hospital death based on the existence of seven variables at admission. The nomogram allowed us to estimate the probability of in-hospital death, and the calibration plot based on these results was well fitted to predict the in-hospital prognosis.

Conclusion

Our nomogram allows physicians to predict individual risk of in-hospital death in patients with asthma exacerbation.

Endotracheal Intubation after Acute Drug Overdoses: Incidence, Complications, and Risk Factors

BACKGROUND

Drug overdose is the leading cause of injury-related fatality in the United States, and respiratory failure remains a major source of morbidity and mortality.

OBJECTIVES

We aimed to identify the incidence and risk factors for endotracheal intubation after acute drug overdose.

METHODS

This secondary data analysis was performed on a 5-year prospective cohort at two urban tertiary-care hospitals. The present study analyzed adult patients with suspected acute drug overdose to derive independent clinical predictors of endotracheal intubation.

RESULTS

We analyzed 2497 patients with acute drug overdose, of whom 87 (3.5%) underwent endotracheal intubation. Independent clinical risk factors for endotracheal intubation were: younger age (odds ratio [OR] 0.97, 95% confidence interval [CI] 0.96-0.98), and history of obstructive lung disease (OR 6.6, 95% CI 3.5-12.3); however, heart failure had no association. Patients with obstructive lung disease had significantly more hypercapnia (mean difference 6.8 mm Hg, 95% CI 2.3-11.3) and a higher degree of acidemia (mean pH difference 0.04, 95% CI 0.01-0.07) than patients without obstructive lung disease. Lack of rapid sequence sedative/paralytic was associated with in-hospital fatality. Early complications of endotracheal intubation itself included desaturation (3.4%) and bradycardia (1%).

CONCLUSIONS

Endotracheal intubation was infrequently performed on patients with acute drug overdose, and complications were rare when performed. Risk factors associated with endotracheal intubation included younger age and prior obstructive lung disease.

Severity Stratification in Life-threatening Asthma

Severity differences may in part explain the large varia tions in asthma mortality that occur in different coun tries. This study examines the use of APACHE II for measuring asthma severity in 118 adult asthma admis sions at one intensive care unit in New Zealand during 1987-1988. Most admissions were hypercapnic (72%), and 61 % had an altered level of consciousness. Mean APACHE II score was 20 in the emergency department and 12 upon ICU admission. We summarize the extent of physiological derangement using four acute physiol ogy score (APS) ranges. Each APS range stratified admis sions into groups with differing clinical course, therapy, and outcome. These results document a high level of asthma severity among patients treated in New Zealand, the country with the world's highest asthma mortality. APACHE II provides a valid and reproducible measure of asthma severity and should be useful for describing and comparing international differences in asthma severity and as a case-mix control in studies of asthma therapy.

Contemporary treatment of children with critical and near-fatal asthma

Asthma is the most common chronic illness in childhood. Although the vast majority of children with acute asthma exacerbations do not require critical care, some fail to respond to standard treatment and require escalation of support. Children with critical or near-fatal asthma require close monitoring for deterioration and may require aggressive treatment strategies. This review examines the available evidence supporting therapies for critical and near-fatal asthma and summarizes the contemporary clinical care of these children. Typical treatment includes parenteral corticosteroids and inhaled or intravenous beta-agonist drugs. For children with an inadequate response to standard therapy, inhaled ipratropium bromide, intravenous magnesium sulfate, methylxanthines, helium-oxygen mixtures, and non-invasive mechanical support can be used. Patients with progressive respiratory failure benefit from mechanical ventilation with a strategy that employs large tidal volumes and low ventilator rates to minimize dynamic hyperinflation, barotrauma, and hypotension. Sedatives, analgesics and a neuromuscular blocker are often necessary in the early phase of treatment to facilitate a state of controlled hypoventilation and permissive hypercapnia. Patients who fail to improve with mechanical ventilation may be considered for less common approaches, such as inhaled anesthetics, bronchoscopy, and extracorporeal life support. This contemporary approach has resulted in extremely low mortality rates, even in children requiring mechanical support.

Mechanical ventilation for severe asthma

Acute exacerbations of asthma can lead to respiratory failure requiring ventilatory assistance. Noninvasive ventilation may prevent the need for endotracheal intubation in selected patients. For patients who are intubated and undergo mechanical ventilation, a strategy that prioritizes avoidance of ventilator-related complications over correction of hypercapnia was first proposed 30 years ago and has become the preferred approach. Excessive pulmonary hyperinflation is a major cause of hypotension and barotrauma. An appreciation of the key determinants of hyperinflation is essential to rational ventilator management. Standard therapy for patients with asthma undergoing mechanical ventilation consists of inhaled bronchodilators, corticosteroids, and drugs used to facilitate controlled hypoventilation. Nonconventional interventions such as heliox, general anesthesia, bronchoscopy, and extracorporeal life support have also been advocated for patients with fulminant asthma but are rarely necessary. Immediate mortality for patients who are mechanically ventilated for acute severe asthma is very low and is often associated with out-of-hospital cardiorespiratory arrest before intubation. However, patients who have been intubated for severe asthma are at increased risk for death from subsequent exacerbations and must be managed accordingly in the outpatient setting.

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.

Critical Asthma Syndrome in the ICU

Critical asthma syndrome represents the most severe subset of asthma exacerbations, and the critical asthma syndrome is an umbrella term for life-threatening asthma, status asthmaticus, and near-fatal asthma. According to the 2007 National Asthma Education and Prevention Program guidelines, a life-threatening asthma exacerbation is marked by an inability to speak, a reduced peak expiratory flow rate of <25 % of a patient's personal best, and a failed response to frequent bronchodilator administration and intravenous steroids. Almost all critical asthma syndrome cases require emergency care, and most cases require hospitalization, often in an intensive care unit. Among asthmatics, those with the critical asthma syndrome are difficult to manage and there is little room for error. Patients with the critical asthma syndrome are prone to complications, they utilize immense resources, and they incite anxiety in many care providers. Managing this syndrome is anything but routine, and it requires attention, alacrity, and accuracy. The specific management strategies of adults with the critical asthma syndrome in the hospital with a focus on intensive care are discussed. Topics include the initial assessment for critical illness, initial ventilation management, hemodynamic issues, novel diagnostic tools and interventions, and common pitfalls. We highlight the use of critical care ultrasound, and we provide practical guidelines on how to manage deteriorating patients such as those with pneumothoraces. When standard asthma management fails, we provide experience-driven recommendations coupled with available evidence to guide the care team through advanced treatment. Though we do not discuss medications in detail, we highlight recent advances.

The critically ill asthmatic--from ICU to discharge

Status asthmaticus (SA) is defined as an acute, severe asthma exacerbation that does not respond readily to initial intensive therapy, while near-fatal asthma (NFA) refers loosely to a status asthmaticus attack that progresses to respiratory failure. The in-hospital mortality rate for all asthmatics is between 1% to 5%, but for critically ill asthmatics that require intubation the mortality rate is between 10% to 25% primarily from anoxia and cardiopulmonary arrest. Timely evaluation and treatment in the clinic, emergency room, or ultimately the intensive care unit (ICU) can prevent the morbidity and mortality associated with respiratory failure. Fatal asthma occurs from cardiopulmonary arrest, cerebral anoxia, or a complication of treatments, e.g., barotraumas, and ventilator-associated pneumonia. Mortality is highest in African-Americans, Puerto Rican-Americans, Cuban-Americans, women, and persons aged ≥ 65 years. Critical care physicians or intensivists must be skilled in managing the critically ill asthmatics with respiratory failure and knowledgeable about the few but potentially serious complications associated with mechanical ventilation. Bronchodilator and anti-inflammatory medications remain the standard therapies for managing SA and NFA patients in the ICU. NFA patients on mechanical ventilation require modes that allow for prolonged expiratory time and reverse the dynamic hyperinflation associated with the attack. Several adjuncts to mechanical ventilation, including heliox, general anesthesia, and extra-corporeal carbon dioxide removal, can be used as life-saving measures in extreme cases. Coordination of discharge and follow-up care can safely reduce the length of hospital stay and prevent future attacks of status asthmaticus.

Status asthmaticus in the medical intensive care unit: a 30-year experience

OBJECTIVES

To investigate the characteristics, trends in management (permissive hypercapnia; mechanical ventilation (MV); neuromuscular blockade) and their impact on complications and outcomes in Status Asthmaticus (SA).

METHODS

We performed a retrospective observational study of subjects admitted with SA to a single multidisciplinary MICU over a 30-year period. All laboratory, radiologic, respiratory care, physician notes and orders were extracted from an electronic medical record (EMR) maintained during the entire duration of the study.

RESULTS

Two hundred and twenty-seven subjects were admitted with 280 episodes of SA. While subjects reflected our regional population (52% Hispanic), African Americans were over-represented (22%) and Caucasians under-represented (21%). Thirty-eight percent reported childhood asthma, 27% were steroid dependent (10% in the last 10 years), and 18% had a recent steroid taper. One hundred and thirty-nine (61.2%) required intubation. The duration of hospitalization was similar between mechanically ventilated and non-ventilated subjects (5.8±4.41 vs. 6.8±7.22 days; p=0.07). The overall complication rate remained low irrespective of the use of permissive hypercapnia or mode of mechanical ventilation (overall mortality 0.4%; pneumothorax 2.5%; pneumonia 2.9%). The frequency of SA declined significantly in the last 10 years of the study (12.4 vs. 3.2 cases/year).

CONCLUSIONS

Despite the frequent use of mechanical ventilation, mortality/complication rates remained extremely low. MV did not significantly increase the duration of hospitalization. At our institution, the frequency of SA significantly decreased despite an increase in emergency room visits for asthma.

Analytic review: management of life-threatening asthma in adults

Asthma remains a troubling health problem despite the availability of effective treatment. A small but significant number of asthmatics experience life-threatening attacks culminating in intensive care unit admission. Standard treatment includes high dose systemic corticosteroids and inhaled bronchodilators. Patients with especially severe attacks may develop respiratory failure and need endotracheal intubation and mechanical ventilation. Severe airway obstruction may lead to dynamic hyperinflation and the possibility of hemodynamic collapse and barotrauma. Fortunately, most intubated asthmatics survive if physicians adhere to key management principles intended to avoid or minimize hyperinflation. The purpose of this review is to discuss the pathogenesis of life-threatening asthma and to provide practical guidance to promote rationale, safe, and effective management.

Acute severe asthma

Acute severe asthma remains a major economic and health burden. The natural history of acute decompensations is one of resolution and only about 0.4% of patients succumb overall. Mortality in medical intensive care units is higher but is less than 3% of hospital admissions. "Near-fatal" episodes may be more frequent, but precise figures are lacking. However, about 30% of medical intensive care unit admissions require intubation and mechanical ventilation with mortality of 8%. Morbidity and mortality increase with socioeconomic deprivation and ethnicity. Seventy to 80% of patients in emergency departments clear within 2 hours with standardized care. The relapse rate varies between 7 and 15%, depending on how aggressively the patient is treated. The airway obstruction in the 20-30% of people resistant to adrenergic agonists in the emergency department slowly reverses over 36-48 hours but requires intense treatment to do so. Current therapeutic options for this group consist of ipratropium and corticosteroids in combination with beta2 selective drugs. Even so, such regimens are not optimal and better approaches are needed. The long-term prognosis after a near-fatal episode is poor and mortality may approach 10%.

Outcome of patients with severe asthma in the intensive care unit

BACKGROUND

Because little has been reported about the outcome of severe asthma outside the US and western Europe, we performed a retrospective case analysis of patients treated in the medical intensive care unit (MICU) of a university hospital in Riyadh, Saudi Arabia, to determine the management, complications and outcome of severe asthma requiring ICU admission.

METHODS

The records of patients with severe asthma admitted to the MICU between the periods of January 1996 to December 2003 were reviewed. Sixty-one episodes from 54 patients were studied, of which 27 (44%) were male.

RESULTS

All patients were hypercapnic; 23 (38%) were ventilated. The Acute Physiological and Health Evaluation (APACHE) score II was significantly higher in the ventilated group (P<0.0001). The pH was significantly lower and PaCO2 was significantly higher in the ventilated group (P<0.0001). All patients survived. Only 42% of patients our series received inhaled corticosteroids before admission.

CONCLUSION

Our results suggest that severe asthma requiring ICU admission is now safely managed in ICUs. Our results are comparable to recently published data on the treatment of severe asthma in the ICU.

Overcoming gaps in the management of asthma in older patients: new insights

Asthma is under-recognised and undertreated in older populations. This is not surprising, given that one-third of older people experience significant breathlessness. The differential diagnosis commonly includes asthma, chronic obstructive pulmonary disease (COPD), heart failure, malignancy, aspiration and infections. Because symptoms and signs of several cardiorespiratory diseases are nonspecific in older people and diseases commonly co-exist, investigations are important. A simple strategy for the investigation of breathlessness in older people should include a full blood count, chest radiograph, ECG, peak flow diary and/or spirometry with reversibility as a minimum. If there are major abnormalities on the ECG, an echocardiogram should also be performed. Diurnal variability in peak flow readings >or=20% or >or=15% reversibility in forced expiratory volume in 1 second, spontaneously or with treatment, support a diagnosis of asthma. Distinguishing asthma from COPD is important to allow appropriate management of disease based on aetiology, accurate prediction of treatment response, correct prognosis and appropriate management of the chest condition and co-morbidities. The two conditions are usually readily differentiated by clinical features, particularly age at onset, variability of symptoms and nocturnal symptoms in asthma, supported by the results of reversibility testing. Full lung function tests may not necessarily help in differentiating the two entities, although gas transfer factor is characteristically reduced in COPD and usually normal or high in asthma. Methacholine challenge tests previously mainly used in research are now also used widely and safely to confirm asthma in clinical settings. Interest in exhaled nitric oxide as a biomarker of airways inflammation is increasing as a noninvasive tool in the diagnosis and monitoring of asthma. Regular inhaled corticosteroids (ICS) are the mainstay of treatment of asthma. Even in mild disease in older adults, regular preventive treatment should be considered, given the poor perception of bronchoconstriction by older asthmatic patients. If symptoms persist despite ICS, addition of long-acting beta(2)-adrenoceptor agonists (LABA) should be considered. Addition of LABA to ICS improves asthma control and allows reduction in ICS dose. However, older people have been grossly under-represented in trials of LABA, many trials having excluded those >or=65 years of age. On meta-analysis, beta(2)-adrenoceptor agonists (both short acting and long acting) are associated with increased cardiovascular mortality and morbidity in asthma and COPD. While the evidence for excess cardiovascular mortality is stronger for short-acting beta(2)-adrenoceptor agonists, it would be prudent to exercise particular care in using beta(2)-adrenoceptor agonists (long acting and short acting) in those at risk of adverse cardiovascular outcomes, including older people. Regular review of cardiovascular status (and monitoring of serum potassium concentration) in patients taking beta(2)-adrenoceptor agonists is crucial. The response to LABA should be carefully monitored and alternative 'add-on' therapy such as leukotriene receptor antagonists (LRA) should be considered. LRA have fewer adverse effects and in individual cases may be more effective and appropriate than LABA. Long-term trials evaluating beta(2)-adrenoceptor agonists and other bronchodilator strategies are needed particularly in the elderly and in patients with cardiovascular co-morbidities. There is no evidence that addition of anticholinergics improves control of asthma further, although the role of long-acting anticholinergics in the prevention of disease progression is currently being researched. Older patients need to be taught good inhaler technique to improve delivery of medications to lungs, minimise adverse effects and reduce the need for oral corticosteroids. Nurse-led education programmes that include a written asthma self-management plan have the potential to improve outcomes.

Clinical review: Mechanical ventilation in severe asthma

Respiratory failure from severe asthma is a potentially reversible, life-threatening condition. Poor outcome in this setting is frequently a result of the development of gas-trapping. This condition can arise in any mechanically ventilated patient, but those with severe airflow limitation have a predisposition. It is important that clinicians managing these types of patients understand that the use of mechanical ventilation can lead to or worsen gas-trapping. In this review we discuss the development of this complication during mechanical ventilation, techniques to measure it and strategies to limit its severity. We hope that by understanding such concepts clinicians will be able to reduce further the poor outcomes occasionally related to severe asthma.

Severe exacerbations of asthma

All asthmatics regardless of their perceived severity, are at risk of exacerbation, particularly if they are suboptimally treated in the outpatient arena. Fortunately most patients recover after administration of bronchodilators and anti-inflammatory medications, but preventable deaths continue to occur and refractory cases result in hospitalization and need for mechanical ventilation. We begin this article by reviewing the pathophysiology of acute exacerbations to build a foundation for the assessment of clinical status and to provide the rationale for a carefully contemplated and evidence-based therapeutic approach. We end this article with an in-depth examination of the particular problems that are encountered during mechanical ventilation and offer a strategy that helps minimize complications. In the final analysis, however, the greatest gains in the field of acute asthma will come not from its treatment but from its prevention by enhanced educational and environmental efforts and by the delivery of optimal medications at home.

Characteristics and outcome for admissions to adult, general critical care units with acute severe asthma: a secondary analysis of the ICNARC Case Mix Programme Database

INTRODUCTION

This report describes the case mix, outcome and activity (duration of intensive care unit [ICU] and hospital stay, inter-hospital transfer, and readmissions to the ICU) for admissions to ICUs for acute severe asthma, and investigates the effect of case mix factors on outcome.

METHODS

We conducted a secondary analysis of data from a high-quality clinical database (the Intensive Care National Audit and Research Centre [ICNARC] Case Mix Programme Database) of 129,647 admissions to 128 adult, general critical care units across England, Wales and Northern Ireland over the period 1995-2001.

RESULTS

Asthma accounted for 2152 (1.7%) admissions, and in 57% mechanical ventilation was employed during the first 24 hours in the ICU. A total of 147 (7.1%) patients died in intensive care and 199 (9.8%) died before discharge from hospital. The mean age was 43.6 years, and the ratio of women to men was 2:1. Median length of stay was 1.5 days in the ICU and 8 days in hospital. Older age, female sex, having received cardiopulmonary resuscitation (CPR) within 24 hours before admission, having suffered a neurological insult during the first 24 hours in the ICU, higher heart rate, and hypercapnia were associated with greater risk for in-hospital death after adjusting for Acute Physiology and Chronic Health Evaluation II score. CPR before admission, neurological insult, hypoxaemia and hypercapnia were associated with receipt of mechanical ventilation after adjusting for Acute Physiology and Chronic Health Evaluation II score.

CONCLUSION

ICU admission for asthma is relatively uncommon but remains associated with appreciable in-hospital mortality. The greatest determinant of poor hospital survival in asthma patients was receipt of CPR within 24 hours before admission to ICU. Clinical management of these patients should be directed at preventing cardiac arrest before admission.

Management of respiratory failure in status asthmaticus

Status asthmaticus is a life-threatening episode of asthma that is refractory to usual therapy. Recent studies report an increase in the severity and mortality associated with asthma. In the airways, inflammatory cell infiltration and activation and cytokine generation produce airway injury and edema, bronchoconstriction and mucus plugging. The key pathophysiological consequence of severe airflow obstruction is dynamic hyperinflation. The resulting hypoxemia, tachypnea together with increased metabolic demands on the muscles of respiration may lead to respiratory muscle failure. The management of status asthmaticus involves intensive pharmacological therapy particularly with beta-adrenoceptor agonists (beta-agonists) and corticosteroids. Albuterol (salbutamol) is the most commonly used beta2-selective inhaled bronchodilator in the US. Epinephrine (adrenaline) or terbutaline, administered subcutaneously, have not been shown to provide greater bronchodilatation compared with inhaled beta-agonists. Corticosteroids such as methylprednisolone should be administered early. Aerosolized corticosteroids are not recommended for patients with status asthmaticus. Inhaled anticholinergic agents may be useful in patients refractory to inhaled beta-agonists and corticosteroids. In patients requiring mechanical ventilation, the strategy aims to avoid dynamic hyperinflation by enhancing expiratory time to allow complete exhalation. Complications of dynamic inflation are hypotension and barotrauma. Sedation with opioids, benzodiazepines or propofol is required to facilitate ventilator synchrony but neuromuscular blockade should be avoided as myopathy has been a reported complication. Overall, in the management of patients with status asthmaticus, the challenge to the pulmonary/critical care clinician is to provide optimal pharmacological and ventilatory support and avoid the adverse consequences of dynamic hyperinflation.

The pulmonary physician in critical care . 12: Acute severe asthma in the intensive care unit

Most deaths from acute asthma occur outside hospital, but the at-risk patient may be recognised on the basis of prior ICU admission and asthma medication history. Patients who fail to improve significantly in the emergency department should be admitted to an HDU or ICU for observation, monitoring, and treatment. Hypoxia, dehydration, acidosis, and hypokalaemia render the severe acute asthmatic patient vulnerable to cardiac dysrrhythmia and cardiorespiratory arrest. Mechanical ventilation may be required for a small proportion of patients for whom it may be life saving. Aggressive bronchodilator (continuous nebulised beta agonist) and anti-inflammatory therapy must continue throughout the period of mechanical ventilation. Recognised complications of mechanical ventilation include hypotension, barotrauma, and nosocomial pneumonia. Low ventilator respiratory rates, long expiratory times, and small tidal volumes help to prevent hyperinflation. Volatile anaesthetic agents may produce bronchodilation in patients resistant to beta agonists. Fatalities in acute asthmatics admitted to HDU/ICU are rare.

The management of acute severe asthma

Asthma is a common cause of morbidity and mortality in the United States, with over two million Emergency Department (ED) visits each year. Airway inflammation is recognized as a major component in the pathophysiology of asthma. The classic presentation of asthma is that of wheezing, cough, and dyspnea, however, the severity of airflow limitation correlates poorly with clinical signs. Forced exhaled volume in 1 s (FEV(1)) and the peak expiratory flow rate (PEFR) are direct reflections of the severity of airflow obstruction and are the standard measures used in the ED to assess the severity of airflow obstruction and the response to therapy. Beta2-adrenergic bronchodilators, ipratropium bromide, and corticosteroids form the cornerstone of therapy. Inhaled corticosteroids, leukotriene modifying drugs, and noninvasive positive pressure ventilation should be considered in patients with severe disease and in those who have responded poorly to standard therapy. Mechanical ventilation is usually well tolerated and may be lifesaving in patients with refractory asthma. Precautions are required to prevent dynamic hyperinflation during assisted ventilation.

Noninvasive positive-pressure ventilation in pediatric status asthmaticus

OBJECTIVE: To describe the use of noninvasive positive-pressure ventilation in children with status asthmaticus. DESIGN: Brief report. SETTING: Pediatric intensive care unit in two tertiary institutions. SUBJECTS: Children with severe acute asthma and hypercarbic respiratory failure. INTERVENTIONS: Noninvasive positive-pressure ventilation using a bilevel positive-pressure (BIPAP) device. MEASUREMENTS AND MAIN RESULTS: Three children, ages 9, 11, and 15 yrs, were treated for hypercarbic respiratory failure caused by status asthmaticus by using BIPAP. The duration of pediatric intensive care unit admission was 48 hrs, and the duration of therapy ranged from 12 to 17 hrs. Inspiratory positive airway pressure ranged from 10 to 14 cm H(2)O (0.98-1.37 kPa), with a mean of 12 cm H(2)O (1.18 kPa). Expiratory positive airway pressure ranged from 4 to 5 cm H(2)O (0.39-0.49 kPa), with a mean of 5 cm H(2)O (0.49 kPa). Pulse oximetry was monitored continuously until resolution of symptoms. The mean values for respiratory rate, pH, and CO(2) tension were compared at initiation, 3-4 hrs, and >12 hrs after beginning BIPAP. BIPAP treatment resulted in improved ventilatory status as shown by an increase in pH from a mean of 7.26 on admission to 7.38 after 3-4 hrs and after 12 hrs, respectively. However, respiratory rate showed a steady decrease from a mean of 31.7 breaths/min on admission to 24 breaths/min at 3-4 hrs and 19 breaths/min at >12 hrs of BIPAP therapy. CO(2) tension (Pco(2)) decreased from a mean value of 54.6 mm Hg (7.28 kPa) on admission to 36.4 mm Hg (4.85 kPa) at 3-4 hrs of treatment; the mean Pco(2) after >12 hrs of treatment was 39.8 mm Hg (5.31 kPa). CONCLUSION: In three children with status asthmaticus, BIPAP seemed to improve ventilation and gas exchange, culminating in resolution of hypercarbic respiratory failure. A prospective, randomized, and controlled study is required to determine its role in pediatric status asthmaticus.

Severe status asthmaticus: management with permissive hypercapnia and inhalation anesthesia

OBJECTIVE

To describe the difficulties that can be encountered during mechanical ventilation of severe status asthmaticus and to discuss the safety of permissive hypercapnia as a ventilatory strategy and the role and limitations of inhalation anesthesia in the treatment of refractory cases.

DESIGN

Case series and review of literature.

SETTING

Intensive care unit of a tertiary care hospital.

PATIENTS

Two patients with severe status asthmaticus.

INTERVENTIONS

Administration of inhalational anesthetics.

MEASUREMENTS AND MAIN RESULTS

Both patients had respiratory failure secondary to status asthmaticus requiring mechanical ventilation and permissive hypercapnia. They also received inhalational anesthetics because of refractory bronchoconstriction. Levels of PaCO(2) in each case were among the highest and most prolonged elevations (>150 mm Hg for several hours) reported to date. In one case, life-threatening difficulties with ventilation were encountered related to the use of an anesthesia ventilator. Although they had complications related to the severity of their illnesses, both were treated to recovery.

CONCLUSIONS

Mechanical ventilation in severe status asthmaticus can be challenging. Permissive hypercapnia is a relatively safe strategy in the ventilatory management of asthma. High levels of hypercapnia and associated severe acidosis are well tolerated in the absence of contraindications (i.e., preexisting intracranial hypertension). Inhalation anesthesia may be useful in the treatment of refractory cases of asthma but should be used carefully because it may be hazardous owing to poor flow capabilities of most anesthesia ventilators.

Changes in fatal and near-fatal asthma in an urban area of South Africa from 1980-1997

Over the past two decades, changes in the health services designed to improve access to and quality of asthma care have occurred in South Africa. The aim of this study was to investigate the incidence of fatal and near-fatal asthma (NFA) from 1980-1997 in an urban part of South Africa. A retrospective analysis of fatal asthma and NFA in the Cape Town City Council area was performed. Mortality data were obtained from death notification records. Data on NFA were obtained from the records of patients admitted for asthma to intensive care units (ICUs) at major academic hospitals serving the area. There were 1,506 deaths (mean age 56 yrs) from asthma reported; 39 and 3% occurred in people under 55 and 15 yrs, respectively. Average annual asthma mortality rate (8.1 +/- 1.9 per 100,000 population) was highest amongst people of mixed race (10.1 +/- 2.0), followed by Blacks (6.8 +/- 3.1) and Whites (5.0 +/- 1.9, p<0.001). Asthma mortality declined by 0.28 deaths per 100,000 population per year; rates decreased in all ethnic groups. Most deaths (72.3%) were outside a health facility and a higher number of deaths occurred on weekends (223 deaths x day(-1)) than weekdays (207 deaths x day(-1), p=0.014). Paediatric asthma ICU admissions declined by 1.81 children yr(-1). The annual number of adults admitted to ICU for asthma, and the proportion requiring intermittent positive pressure ventilation did not change. These results indicate that the incidence of fatal and near-fatal asthma in this area has declined over the period and this may reflect improved asthma management. However, the relatively high asthma mortality rate in people of mixed race and the predominance of deaths outside health facilities and on weekends suggest problems with access to care.

Status asthmaticus in children: a review

About 10% of American children have asthma, and its prevalence, morbidity, and mortality have been increasing. Asthma is an inflammatory disease with edema, bronchial constriction, and mucous plugging. Status asthmaticus in children requires aggressive treatment with beta-agonists, anticholinergics, and corticosteroids. Intubation and mechanical ventilation should be avoided if at all possible, as the underlying dynamic hyperinflation will worsen with positive-pressure ventilation. If mechanical ventilation becomes necessary, controlled hypoventilation with low tidal volume and long expiratory time may lessen the risk of barotrauma and hypotension. Unusual and nonestablished therapies for severe asthma are discussed.

Influence of gender on rates of hospitalization, hospital course, and hypercapnea in high-risk patients admitted for asthma : a 10-year retrospective study at Yale-New Haven Hospital

STUDY OBJECTIVES

To compare the relative numbers and hospital course of men vs women admitted at least twice with asthma or status asthmaticus to Yale-New Haven Hospital (YNHH) during the period from 1985 to 1994.

DESIGN

A retrospective chart review.

SETTING

YNHH.

PATIENTS

High-risk men and women (age range, 18 to 50 years) admitted at least twice during the study period with the discharge diagnosis of asthma or status asthmaticus.

RESULTS

Of 561 adult asthma patients admitted during the study period, 188 were admitted at least twice and accounted for 68% of the total asthma admissions. One hundred three of the 188 patients were randomly selected, and all of their asthma admissions were retrospectively reviewed. The 103 patients accounted for 382 admissions. Seventy-two percent of these patients and 68.6% of the admissions were women. The proportions of each gender requiring admission to the medical ICU (15.65% women vs 11.67% men) or intubation (8.00% women vs 5.80% men) were not significantly different. Women did exhibit a definite trend toward longer admissions (4.92 days vs 4.04 days; p < 0.554). A significantly higher proportion of female patient admissions underwent initial arterial blood gas analysis than men (56.9% vs 44.2%; p < 0.05). Factorial analysis demonstrated a highly significant main effect of gender on PCO(2) levels (p < 0.0001). Men, overall, had higher PCO(2) levels than women (48.73 mm Hg vs 41.04 mm Hg; p < 0.036). Male patients admitted to the medical ICU or requiring intubation had significantly higher PCO(2) levels than their respective female counterparts (p < 0.05).

CONCLUSIONS

At YNHH, 68% of all admissions for asthma in this age group are attributable to high-risk patients. High-risk female patients are admitted twice as often as high-risk male patients and tend to have longer admissions. Once admitted, however, the proportion of men and women requiring the medical MICU or intubation were similar. High-risk male patients on presentation are consistently more hypercapneic than high-risk female patients. Therefore, the mechanisms contributing to the gender differences in asthma admissions may include differences in the ventilatory response to hypercapnea or in the tolerance to airway obstruction.

The pathobiology of acute asthma

Acute bronchial asthma is a common problem with immense medical and economic impacts. It is estimated that this disease affects 12 to 14 million people in the United States with costs in excess of $6 billion per year. Most of the morbidity and all of the mortality of asthma tends to be associated with acute exacerbations, and treatment of these events accounts for the majority of expenditures in money and health care resources. Unfortunately, the factors that contribute to the destabilization of asthma are rarely studied and much of the pathogenesis and pathobiology of acute asthma remains unknown. This article examines these issues and suggests treatment for acute asthma.

Uncontrolled oxygen administration and respiratory failure in acute asthma

STUDY OBJECTIVES

To determine if 100% oxygen administration adversely influences gas exchange in acutely ill asthmatic subjects.

DESIGN

Prospective preinterventional and postinterventional comparison.

SETTING

University hospital emergency department.

PATIENTS

Thirty-seven asthmatic subjects seeking care for symptomatic exacerbations.

INTERVENTIONS

Twenty minutes of 100% oxygen administration by face mask.

MEASUREMENTS AND RESULTS

Arterial blood gases and FEV(1) were measured before and during the last minute of oxygen administration. On presentation, the subjects had moderately severe airway obstruction (FEV(1), 49.1 +/- 3.6% of predicted); hypocarbia (PaCO(2), 36.8 +/- 1.1 mm Hg); hypoxemia (PaO(2), 70.2 +/- 2.5 mm Hg); and respiratory alkalosis (pH, 7.43 +/- 0.01). During oxygen breathing, 25 patients (67.6%) experienced elevations in PaCO(2) ranging from 1 to 10 mm Hg (mean, 4.1 +/- 0.6 mm Hg; p = 0.0003). The increase was considered to be a physiologic manifestation of the Haldane effect (ie, < or = 2 mm Hg) in 10 subjects, but in the remaining 15 subjects (40.5% of the total studied), the elevation represented worsening gas exchange. In seven of these patients (46.7%), hypercapnic respiratory failure developed (PaCO(2) before oxygen, 39.6 +/- 0.6; during oxygen, 44.7 +/- 0.7 mm Hg; p = 0.005), and in six patients (40%), it worsened (PaCO(2) before oxygen, 46.8 +/- 1.9; during oxygen, 52.0 +/- 3.1 mm Hg; p = 0.03). In general, the tendency toward hypercarbia was the greatest in the participants with the most severe airway obstructions.

CONCLUSIONS

Our data demonstrate that the administration of 100% oxygen to acutely ill asthmatics may adversely influence carbon dioxide elimination.

Management of respiratory failure in patients with asthma

The goal of management of patients with respiratory failure is to restore them to a state of quiet breathing, without complication. This goal is often achieved by pharmacotherapy alone. Inhaled albuterol sulfate, oxygen, and systemic corticosteroids are mainstays of acute care drug management, whereas other data support the use of inhaled steroids, ipratropium bromide, magnesium sulfate, theophylline, and heliox. Assisted ventilation by face mask or endotracheal tube may be required in refractory patients. In intubated patients, a ventilatory strategy that prolongs exhalation time and accepts hypercapnia minimizes lung hyperinflation and generally results in a good outcome. Acute asthma often represents failure of outpatient management; key aspects of the outpatient program should be addressed in the acute care setting to help prevent recurrent attacks.

Ventilation of patients with asthma and obstructive lung disease

Mechanical ventilation in a patient with obstructive airway disease may be a lifesaving measure; however, it may also be associated with significant morbidity and mortality. It is important for a physician to be familiar with the potential complications of mechanical ventilation in this group of patients and to know how to avoid them by carefully applying safe ventilator strategies. The cornerstone of such strategies is to minimize minute ventilation, maximize time for expiration, and avoid hyperinflation of the lung. Several bedside parameters (iPEEP, VEI, Pplat) that reflect presence of gas trapping and potential hyperinflation may be measured. In addition to mechanical ventilation, management should include inhaled bronchodilators and systemic corticosteroid therapies. In the event controlled hypoventilation is necessary, sedation with or without the use of muscle relaxants may be required. Unconventional therapies such as the use of Heliox, magnesium sulfate, ketamine, and inhalational anesthetics may be attempted in severe cases that do not respond to conventional management. With appropriate use of ventilator strategies, a reduction in the mortality and morbidity of patients with obstructive airway disease requiring mechanical ventilation has recently been noted.

An evidence-based approach to noninvasive ventilation in acute respiratory failure

This article reviews the literature of noninvasive positive pressure ventilation (NPPV) in patients with acute respiratory failure. The article divides acute respiratory failure into the categories of primary ventilation failure and oxygenation failure, and examines various diagnostic groups within these categories. Although the use of NPPV for patients with acute respiratory failure of other etiologies requires further study, the authors conclude that there is sufficient evidence to support the use of NPPV in acute, severe exacerbations of chronic obstructive pulmonary disease.

Medical and ventilatory management of status asthmaticus

Despite improved understanding of the basic mechanisms underlying asthma, morbidity and mortality remain high, especially in the "inner cities." The treatment of choice in status asthmaticus includes high doses of inhaled beta 2-agonists, systemic corticosteroids, and supplemental oxygen. The roles of theophylline and anticholinergics remain controversial, although in general these agents appear to add little to the bronchodilator effect of inhaled beta-agonists in most patients. Anti-leukotriene medications have not yet been evaluated in acute asthma. Other therapies, such as magnesium sulfate and heliox, have their advocates but are not recommended as part of routine care. If pharmacological therapy does not reverse severe airflow obstruction in the asthmatic attack, mechanical ventilation may be temporarily required. Based on our current understanding of ventilator-induced lung injury, optimal ventilation of asthmatic patients avoids excessive lung inflation by limiting minute ventilation and prolonging expiratory time, despite consequent hypercapnia. Unless respiratory function is extremely unstable, the use of paralytic agents is discouraged because of the increased risk of intensive care myopathy. Patients who have suffered respiratory failure due to asthma are at increased risk for subsequent death due to asthma (14% mortality at 3 years) and should receive very close medical follow-up. In general, severe asthmatic attacks can best be prevented by early intervention in the outpatient setting. In the words of Dr. Thomas Petty, "... the best treatment of status asthmaticus is to treat it three days before it occurs".