Asthma requiring mechanical ventilation. A low morbidity approach

Asthma Outcomes and Management During Pregnancy

Asthma during pregnancy poses a common, increasingly prevalent threat to the health of women and their children. The present article reviews recent insights gained from the epidemiology of asthma during pregnancy, demonstrating the many short- and long-term risks to mother and fetus incurred by poorly controlled maternal asthma. We further discuss emerging evidence that active management of asthma during pregnancy can positively influence and perhaps completely mitigate these poor outcomes. Recent high-quality trials examining best methods for asthma treatment are reviewed and synthesized to offer an evidence-based pathway for comprehensive treatment of asthma in the outpatient setting. Safe and effective medications, as well as nonpharmacologic interventions, for asthma during pregnancy are discussed, and treatment options for related conditions of pregnancy, including depression, rhinitis, and gastroesophageal reflux, are presented. Throughout, we emphasize that an effective treatment strategy relies on a detailed patient evaluation, patient education, objective measurement of asthma control, and frequent and supportive follow-up. The cardiovascular and respiratory physiology of pregnancy is reviewed, as well as its implications for the management of patients with asthma, including patients requiring intubation and mechanical ventilation. For the situation when outpatient asthma management has failed, an approach to the critically ill pregnant patient with status asthmaticus is detailed. Multidisciplinary teams that include pulmonary specialists, obstetricians, primary care providers, nurses, pharmacists, and asthma educators improve the care of pregnant women with asthma.

Managing Respiratory Failure in Obstructive Lung Disease

Exacerbations of obstructive lung disease are common causes of acute respiratory failure. Short-acting bronchodilators and systemic glucocorticoids are the foundation of pharmacologic management. For patients requiring ventilator support, use of noninvasive ventilation reduces the risk of mortality and progression to invasive mechanical ventilation. Challenges associated with invasive ventilation include ventilator dyssynchrony, air trapping, and dynamic hyperinflation. Careful monitoring and adjustment of ventilatory support parameters helps to optimize the patient-ventilator interaction and minimizes the risk of associated morbidity. Extracorporeal life support is an emerging treatment for refractory hypercapnic respiratory failure associated with obstructive lung disease.

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.

Pediatric Respiratory Emergencies

Respiratory emergencies are 1 of the most common reasons parents seek evaluation for the their children in the emergency department (ED) each year, and respiratory failure is the most common cause of cardiopulmonary arrest in pediatric patients. Whereas many respiratory illnesses are mild and self-limiting, others are life threatening and require prompt diagnosis and management. Therefore, it is imperative that emergency clinicians be able to promptly recognize and manage these illnesses. This article reviews ED diagnosis and management of foreign body aspiration, asthma exacerbation, epiglottitis, bronchiolitis, community-acquired pneumonia, and pertussis.

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.

Anesthesia and ventilation strategies in children with asthma: part II - intraoperative management

PURPOSE OF REVIEW

As asthma is a frequent disease especially in children, anesthetists are increasingly providing anesthesia for children requiring elective surgery with well controlled asthma but also for those requiring urgent surgery with poorly controlled or undiagnosed asthma. This second part of this two-part review details the medical and ventilatory management throughout the perioperative period in general but also includes the perioperative management of acute bronchospasm and asthma exacerbations in children with asthma.

RECENT FINDINGS

Multiple observational trials assessing perioperative respiratory adverse events in healthy and asthmatic children provide the basis for identifying risk reduction strategies. Mainly, animal experiments and to a small extent clinical data have advanced our understanding of how anesthetic agents effect bronchial smooth muscle tone and blunt reflex bronchoconstriction. Asthma treatment outside anesthesia is well founded on a large body of evidence.Perioperative prevention strategies have increasingly been studied. However, evidence on the perioperative management, including mechanical ventilation strategies of asthmatic children, is still only fair, and further research is required.

SUMMARY

To minimize the considerable risk of perioperative respiratory adverse events in asthmatic children, perioperative management should be based on two main pillars: the preoperative optimization of asthma treatment (please refer to the first part of this two-part review) and - the focus of this second part of this review - the optimization of anesthesia management in order to optimize lung function and minimize bronchial hyperreactivity in the perioperative period.

Characteristics of asthma patients admitted to an intermediate respiratory care unit

INTRODUCTION

Intermediate respiratory care units (IRCU) provide continuous monitoring and non-invasive mechanical ventilation (NIMV) in patients with severe respiratory failure who are usually admitted to intensive care units (ICU). The usefulness of IRCU in managing severe asthma exacerbations has never been evaluated.

METHODS

Clinical data were prospectively and systematically compiled from patients admitted to the IRCU with a principal diagnosis of bronchial asthma exacerbation. We assessed therapeutic failure (intubation or exitus) and patient evolution up until 6 months after discharge compared with a group of patients admitted to a conventional hospital ward, paired for age and sex, and with the same principal diagnosis.

RESULTS

A total of 74 asthma patients were included (37 admitted to IRCU and 37 to the hospital ward) with a mean age (±SD) of 58±20, who were predominantly women (67%), with previous diagnosis of asthma and persistent asthma treatment. The main cause of admittance to the IRCU was severe respiratory failure. The patients who were admitted to the IRCU presented more radiological affectation (alveolar infiltrates) and had significantly higher pCO(2). Ten patients admitted to the IRCU required NIMV. There were no differences between the two groups regarding either therapeutic failure or the 6-month follow-up after discharge.

CONCLUSIONS

Patients with severe asthma exacerbations can be managed in an IRCU while avoiding hospitalization in an ICU and demonstrating a prognosis similar to milder exacerbations treated in conventional hospital wards.

Pediatric fiberoptic bronchoscopy as adjunctive therapy in acute asthma with respiratory failure

BACKGROUND

Status asthmaticus respiratory failure is associated with thickened mucus secretions necessitating aggressive pulmonary clearance. The role of bronchoscopy in pediatric mechanically ventilated asthmatic patients has not been published.

METHODS

A chart review was performed on all pediatric intensive care unit (PICU) asthmatics with respiratory failure over 13 years. Forty-four patients were identified. Patients were managed per standardized guidelines for status asthmaticus with mechanical ventilation. Ventilator management prioritized spontaneous breathing with pressure support. Extubation criteria included spontaneous tidal volumes of 5-7 cm(3) /kg on low-pressure support. Standard endotracheal tube pulmonary toilet were implemented. Twenty-nine patients underwent bronchoscopy as an adjunctive therapy. Indications for bronchoscopy included: Pathogen identification via bronchoalveolar ravage, atelectasis, mucus obstruction resulting in severe air trapping, suspected aspiration, and poor response to standard therapy. Clinical outcomes of this intervention were compared to the fifteen patient cohort who did not undergo bronchoscopy.

RESULTS

Bronchoscopies revealed thick mucus plugs, secretions, and bronchial casts. The large airways were lavaged for clearance of obstructive secretions with normal saline. All patients tolerated the procedure without any complications. Demonstrable improvement in pulmonary compliance was noted. The median time of intubation for the bronchoscopy group was 10 hr compared to 20.5 hr for the control group (P < 0.0005). The mean intensive care unit length of stay was 3.06 days for the bronchoscopy group versus 3.4 days for the non-bronchoscopy group (P < 0.05).

CONCLUSION

Flexible bronchoscopy with bronchial lavage is a safe adjunctive therapy in pediatric asthmatics with respiratory failure resulting in reduced mechanical ventilation and intensive care length of stay. Restoring lung volume in certain asthmatics during respiratory failure may be deemed beneficial. Further validated studies are necessary to recommend bronchoscopy to the present, accepted treatment regimen in pediatric asthmatic respiratory failure.

Common pediatric respiratory emergencies

Pediatric respiratory illnesses are a huge burden to emergency departments worldwide. This article reviews the latest evidence in the epidemiology, assessment, management, and disposition of children presenting to the emergency department with asthma, croup, bronchiolitis, and pneumonia.

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.

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.

Aspirin-sensitive respiratory disease

Aspirin-sensitive respiratory disease (ASRD) is a condition characterized by persistent and often severe inflammation of the upper and lower respiratory tracts. Patients develop chronic eosinophilic rhinosinusitis, nasal polyposis, and asthma. The ingestion of aspirin and other cyclooxygenase-1 (COX-1) inhibitors induces exacerbations of airway disease that may be life-threatening. Thus, aspirin sensitivity is a phenotypic marker for the syndrome, yet nearly all affected individuals can be desensitized by the administration of graded doses of aspirin, leading to long-term clinical benefits. Patients with aspirin sensitivity are often able to tolerate selective COX-2 inhibitors. The pathogenesis of ASRD is underpinned by abnormalities in eicosanoid biosynthesis and eicosanoid receptor expression coupled with intense mast cell and eosinophilic infiltration of the entire respiratory tract. This review focuses on the molecular, cellular, and biochemical abnormalities characterizing ASRD and highlights unanswered questions in the literature and potential future areas of investigation.

Experience with use of extracorporeal life support for severe refractory status asthmaticus in children

Introduction

Severe status asthmaticus (SA) in children may require intubation and mechanical ventilation with a subsequent increased risk of death. In the patient with SA and refractory hypercapnoeic respiratory failure, use of extracorporeal life support (ECLS) has been anecdotally reported for carbon dioxide removal and respiratory support. We aimed to review the experience of a single paediatric centre with the use of ECLS in children with severe refractory SA, and to compare this with international experience from the Extracorporeal Life Support Organization (ELSO) registry.

Methods

All paediatric patients (aged from 1 to 17 years) with primary International Classification of Diseases (ICD)-9 diagnoses of SA receiving ECLS for respiratory failure from both the Children's Healthcare of Atlanta at Egleston (Children's at Egleston) database and the ELSO registry were reviewed.

Results

Thirteen children received ECLS for refractory SA at the Children's at Egleston from 1986 to 2007. The median age of the children was 10 years (range 1 to 16 years). Patients generally received aggressive use of medical and anaesthetic therapies for SA before cannulation with a median partial pressure of arterial carbon dioxide (PaCO₂) of 130 mmHg (range 102 to 186 mmHg) and serum pH 6.89 (range 6.75 to 7.03). The median time of ECLS support was 95 hours (range 42 to 395 hours). All 13 children survived without neurological sequelae. An ELSO registry review found 64 children with SA receiving ECLS during the same time period (51 excluding the Children's at Egleston cohort). Median age, pre-ECLS PaCO₂ and pH were not different in non-Children's ELSO patients. Overall survival was 60 of 64 (94%) children, including all 13 from the Children's at Egleston cohort. Survival was not significantly associated with age, pre-ECLS PaCO₂, pH, cardiac arrest, mode of cannulation or time on ECLS. Significant neurological complications were noted in 3 of 64 (4%) patients; patients with neurological complications were not significantly more likely to die (P = 0.67).

Conclusions

Single centre and ELSO registry experience provide results of a cohort of children with refractory SA managed with ECLS support. Further study is necessary to determine if use of ECLS in this setting produces better outcomes than careful mechanical ventilation and medical therapy alone.

Mechanical ventilation for asthma: a 10-year experience

BACKGROUND

Asthmatics requiring admission to the intensive care unit and/or mechanical ventilation have increased morbidity and mortality. The purpose of this study is to examine morbidity and mortality in patients requiring intubation and mechanical ventilation for asthma over a 10-year period. This study also reviews the clinical features and management of these patients.

METHODS

We performed a retrospective review of medical records over a 10-year period of adult patients who required mechanical ventilation for a primary diagnosis of asthma. The study was conducted at a university-affiliated, county hospital.

RESULTS

One hundred twenty-seven patients with 162 episodes of asthma requiring mechanical ventilation were identified. The majority of the patients (64%) were women. The predominant ethnicity was African-American (65%). These patients had multiple risk factors for asthma mortality, including recent hospital admissions, prior episodes of near-fatal asthma, medication non-compliance, and poor outpatient follow-up. Over the 10 years of the study, outpatient management of these patients changed, with the percentage of admissions in which patients had been given inhaled corticosteroids increasing from 18 percent in 1990 to 80 percent in 1998. Management of mechanical ventilation also changed. The average tidal volume settings significantly decreased after 1995. The most common complication was atelectasis, which was seen in 33 cases. Evidence of barotrauma, including pneumothorax, pneumomediastinum, and subcutaneous emphysema, was present in 10 cases. There were four deaths. All four of the patients suffered cardiopulmonary arrest in the field with subsequent anoxic brain injury and withdrawal of care.

CONCLUSIONS

Although these patients had multiple risk factors for mortality from asthma, no deaths in this study were related to complications of mechanical ventilation. This low mortality may be related to changes in management of mechanical ventilation as well as changes in chronic outpatient asthma therapy.

Improved outcomes from acute severe asthma in Australian intensive care units (1996 2003)

BACKGROUND

There is limited information on changes in the epidemiology and outcome of patients with asthma admitted to intensive care units (ICUs) in the last decade. A database sampling intensive care activity in hospitals throughout Australia offers the opportunity to examine these changes.

METHODS

The Australian and New Zealand Intensive Care Society Adult Patient Database was examined for all patients with asthma admitted to ICUs from 1996 to 2003. Demographic, physiological and outcome information was obtained and analysed from 22 hospitals which had submitted data continuously over this period.

RESULTS

ICU admissions with the primary diagnosis of asthma represented 1899 (1.5%) of 126 906 admissions during the 8-year period. 36.1% received mechanical ventilation during the first 24 h. The overall incidence of admission to ICU fell from 1.9% in 1996 to 1.1% in 2003 (p<0.001). Overall hospital mortality was 3.2%. There was a significant decline in mortality from a peak of 4.7% in 1997 to 1.1% in 2003 (p = 0.014). This was despite increasing severity of illness (as evidenced by an increasing predicted risk of death derived from the APACHE II score) over the 8-year period (p = 0.002).

CONCLUSIONS

There has been a significant decline in the incidence of asthma requiring ICU admission between 1996 and 2003 among units sampled by the Australian and New Zealand Intensive Care Society Adult Patient Database. The mortality of these patients has also decreased over time and is lower than reported in other studies.

Brief review: Nondepolarizing neuromuscular blocking drugs and critical illness myopathy

PURPOSE

Critically-ill patients who receive nondepolarizing neuromuscular blocking drugs (NMBDs) may be at risk of developing profound muscle weakness that may last for months after the NMBD is discontinued, especially when large cumulative doses of NMBDs and corticosteroids are co-administered to septic, mechanically ventilated patients. This review focuses on the etiology and clinical features of critical illness myopathy (CIM), summarizes specific risk factors for its development, and discusses strategies that might be used to attenuate or even prevent the development of this potentially devastating syndrome.

CLINICAL FEATURES

The etiology of CIM is unknown. Whether it can develop in at-risk patients who undergo lengthy operations during which they receive NMBDs is also unknown. In some patients following exposure to NMBDs their motor systems are impaired secondary to loss of thick (myosin) filaments that render the muscle unexcitable to direct electrical stimulation, while the sensory system is spared. Management of patients who develop NMBD myopathy is supportive, consisting of nutritional support, physical therapy, and daily trials of decreased ventilatory support.

CONCLUSION

Recent guidelines recommend that NMBDs be used in critically ill patients only when absolutely necessary, that the depth of muscle paralysis be monitored to avoid overdosing and metabolite accumulation, and that drug administration be curtailed periodically to allow interruption of sustained NMBD effect.

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.

A rational approach to the management of severe refractory asthma

Severe refractory asthma is a heterogeneous condition with different patterns of severity and different reasons for loss of asthma control. The three main patterns include asthma with frequent exacerbations, asthma with irreversible airway obstruction, and asthma with reduced sensitivity or resistance to corticosteroids. Each of these patterns has distinct risk factors. The assessment of patients with severe asthma requires a systematic, diagnostic and management protocol. The majority of patients will benefit from thorough analysis and treatment of aggravating factors. In some patients with severe refractory asthma, in particular those with concomitant chronic rhinosinusitis, long-term administration of systemic corticosteroids may be necessary. In these patients all efforts should be directed towards reducing the dose of corticosteroids as much as possible. Although several corticosteroid-sparing agents and immunosuppressants have been proposed in the literature, none of these has gained complete acceptance in clinical practice, either because of limited efficacy or unacceptable adverse effects. Novel potent anti-inflammatory therapies aimed at reducing the need for systemic corticosteroids in patients with severe, refractory asthma are urgently needed.

Management of mechanical ventilation in acute severe asthma: practical aspects

BACKGROUND

Acute severe asthma induces marked alterations in respiratory mechanics, characterized by a critical limitation of expiratory flow and a heterogeneous and reversible increase in airway resistance, resulting in premature airway closure, lung, and chest wall dynamic hyperinflation and high intrinsic PEEP.

DISCUSSION

These abnormalities increase the work of breathing and can lead to respiratory muscle fatigue and life-threatening respiratory failure, in which case mechanical ventilation is life-saving. When instituting mechanical ventilation in this setting, a major concern is the risk of worsening lung hyperinflation (thereby provoking barotrauma) and inducing or aggravating hemodynamic instability. Guidelines for mechanical ventilation in acute severe asthma are not supported by strong clinical evidence. Controlled hypoventilation with permissive hypercapnia may reduce morbidity and mortality compared to conventional normocapnic ventilation. Profound pathological alterations in respiratory mechanics occur during acute severe asthma, which clinicians should keep in mind when caring for ventilated asthmatics.

CONCLUSION

We focus on the practical management of controlled hypoventilation. Particular attention must be paid to ventilator settings, monitoring of lung hyperinflation, the role of extrinsic PEEP, and administering inhaled bronchodilators. We also underline the importance of deep sedation with respiratory drive-suppressing opioids to maintain patient-ventilator synchrony while avoiding as much as can be muscle paralysis and the ensuing risk of myopathy. Finally, the role of noninvasive positive pressure ventilation for the treatment of respiratory failure during severe asthma is discussed.

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.

Effect of prolongation of expiratory time on dynamic hyperinflation in mechanically ventilated patients with severe asthma

OBJECTIVE

To assess the effect of a decrease in respiratory rate on dynamic hyperinflation, as determined by changes in plateau airway pressure, in patients with status asthmaticus whose baseline minute ventilation approximated 10 L/min.

DESIGN

Observational descriptive study.

SETTING

Medical intensive care unit.

PATIENTS

Twelve patients with severe asthma mechanically ventilated in the assist control mode with a tidal volume of 613 +/- 100 mL and an inspiratory flow rate of 79 +/- 4 L/min.

INTERVENTIONS

A decrease in respiratory rate from 18 to 12 and 6 breaths/min.

MEASUREMENTS AND MAIN RESULTS

Plateau airway pressure decreased by approximately 2 cm H2O (25.4 +/- 2.8 vs. 23.3 +/- 2.6 cm H2O, p <.01) when respiratory rate was decreased from 18 to 12 breaths/min (increase in expiratory time 1.7 secs) and by a similar amount (23.3 +/- 2.6 vs. 21.3 +/- 2.9 cm H2O, p <.01) when respiratory rate was decreased from 12 to 6 breaths/min (increase in expiratory time 5 secs). Peak airway pressure was similar at the three respiratory rates (66.8 +/- 8.7 vs. 66.4 +/- 9.5 vs. 67.8 +/- 11.1 cm H2O at 18, 12, and 6 breaths/min, respectively). End-expiratory flow rates (n = 7) were 61.4 +/- 12.6, 38.6 +/- 4.5, and 23.1 +/- 5.8 mL/sec at respiratory rates of 18, 12, and 6 breaths/min, respectively.

CONCLUSIONS

Prolongation of expiratory time decreases dynamic hyperinflation in patients with status asthmaticus, as evidenced by a reduction in plateau airway pressure, but the magnitude of this effect is relatively modest when baseline minute ventilation is < or = 10 L/min, because of the low end-expiratory flow rates. Since flow progressively decreases throughout expiration, the reduction in dynamic hyperinflation resulting from a given prolongation of expiratory time will depend on the baseline respiratory rate (i.e., less reduction in dynamic hyperinflation at a lower respiratory rate). Changes in peak airway pressure may not always reflect the changes in dynamic hyperinflation that result from prolongation of expiratory time.

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.

Pressure-controlled ventilation in children with severe status asthmaticus

OBJECTIVE

The optimum strategy for mechanical ventilation in a child with status asthmaticus is not established. Volume-controlled ventilation continues to be the traditional approach in such children. Pressure-controlled ventilation may be theoretically more advantageous in allowing for more uniform ventilation. We describe our experience with pressure-controlled ventilation in children with severe respiratory failure from status asthmaticus.

DESIGN

Retrospective review.

SETTING

Pediatric intensive care unit in a university-affiliated children's hospital.

PATIENTS

All patients who received mechanical ventilation for status asthmaticus.

INTERVENTIONS

Pressure-controlled ventilation was used as the initial ventilatory strategy. The optimum pressure control, rate, and inspiratory and expiratory time were determined based on blood gas values, flow waveform, and exhaled tidal volume.

MEASUREMENT AND MAIN RESULTS

Forty patients were admitted for 51 episodes of severe status asthmaticus requiring mechanical ventilation. Before the institution of pressure-controlled ventilation, median pH and Pco(2) were 7.21 (range, 6.65-7.39) and 65 torr (29-264 torr), respectively. Four hours after pressure-controlled ventilation, median pH increased to 7.31 (6.98-7.45, p <.005), and Pco(2) decreased to 41 torr (21-118 torr, p <.005). For patients with respiratory acidosis (Pco(2) >45 torr) within 1 hr of starting pressure-controlled ventilation, the median length of time until Pco(2) decreased to <45 torr was 5 hrs (1-51 hrs). Oxygen saturation was maintained >95% in all patients. Two patients had pneumomediastinum before pressure-controlled ventilation. One patient each developed pneumothorax and subcutaneous emphysema after initiation of pressure-controlled ventilation. All patients survived without any neurologic morbidity. Median duration of mechanical ventilation was 29 hrs (4-107 hrs), intensive care stay was 56 hrs (17-183 hrs), and hospitalization was 5 days (2-20 days).

CONCLUSIONS

Based on this retrospective study, we suggest that pressure-controlled ventilation is an effective ventilatory strategy in severe status asthmaticus in children. Pressure-controlled ventilation represents a therapeutic option in the management of such children.

[Ventilation in special situations. Mechanical ventilation in status asthmaticus]

The indications for mechanical ventilation in status asthmaticus are cardiopulmonary arrest, significant alteration of consciousness, respiratory exhaustion, and progressive respiratory insufficiency despite aggressive bronchodilator treatment. In mechanical ventilation for status asthmaticus, a specific strategy directed at reducing dynamic hyperinflation must be used, with low tidal volumes and long expiratory times, achieved by diminishing respiratory frequency. This ventilatory pattern produces permissive hypercapnia, which is generally well tolerated with suitable sedation. The best methods for detecting and/or controlling dynamic hyperinflation in ventilated patients with status asthmaticus are the flow/time and flow/volume respiratory curves, pulmonary volume at the end of inspiration, and the pressure plateau. In addition to mechanical ventilation the child must receive sedation with or without a muscle relaxant to prevent barotrauma and accidental extubation. Bronchodilator treatment with beta-adrenergic agonists, methyl-prednisolone, and intravenous aminophylline are also required. A combination of inhaled salbutamol and nebulized ipratropium in the inspiratory branch of the ventilator should be used in patients in whom this treatment is effective. Currently there is insufficient evidence on the efficiency of other treatments in status asthmaticus and these should be used as rescue treatments.

Correlates of prolonged hospitalization in inner-city ICU patients receiving noninvasive and invasive positive pressure ventilation for status asthmaticus

STUDY OBJECTIVES

To describe the outcome of patients with status asthmaticus (SA) treated in a medical ICU with positive pressure ventilation (PPV), and to identify those factors associated with increased length of hospital stay.

DESIGN

Retrospective chart review.

SETTING

University-based hospital in Chicago, IL.

PATIENTS

All patients admitted with SA and treated with PPV over a 5-year period.

RESULTS

The first ICU admission for each of 78 patients was analyzed. Fifty-six patients underwent endotracheal intubation (ETI) during the hospitalization, while 22 patients were treated with noninvasive PPV alone. Three patients died. The median hospital length of stay was 5.5 days. Cox regression analysis revealed the following factors to be independently associated with increased length of hospital stay: female gender (p < 0.01), ETI (p < 0.01), the administration of neuromuscular blockers for > 24 h (p < 0.01), inhaled corticosteroid use prior to ICU admission (p = 0.01), and increasing APACHE (acute physiology and chronic health evaluation) II score (p < 0.01).

CONCLUSIONS

This study suggests that while the mortality associated with SA treated with contemporary methods of PPV is low, certain factors, including female gender, ETI, and the prolonged use of neuromuscular blockade, are associated with an increased length of hospital stay. The development of respiratory failure despite preadmission use of inhaled corticosteroids is also associated with prolonged hospitalization.

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.

Clinical course and outcome of patients admitted to an ICU for status asthmaticus

STUDY OBJECTIVES

To describe the prognostic factors, clinical course, and outcome of patients with status asthmaticus treated in a medical ICU (MICU).

DESIGN

Analysis of prospective data.

SETTING

A multidisciplinary MICU of an inner-city university hospital.

PATIENTS

We collected data on 132 hospital admissions of 89 patients with status asthmaticus treated in our MICU from August 1995 through July 1998.

MEASUREMENTS

APACHE (acute physiology and chronic health evaluation) II scores were among the parameters measured.

RESULTS

Seventy-nine percent of the patients were female, and 67% were African American (mean +/- SD age, 42.4 +/- 15.1 years). Patients in 48 of the 132 hospital admissions (36%) required invasive mechanical ventilation; sepsis developed in patients during 17 hospital admissions (13%), nonpulmonary organ failure developed during 16 hospital admissions (12%), and ARDS developed during 2 hospital admissions (2%). Pneumothorax developed in four patients and required tube thoracostomy in all four patients. The median APACHE II score was 11. Predicted mortality and actual mortality were 6.7% and 8.3%, respectively. The two most common immediate causes of death were pneumothorax (n = 3) and nosocomial infection (n = 3). All the deaths occurred in female patients. Compared with survivors, nonsurvivors had higher APACHE II scores (median, 26 vs 15; p < 0.0001), PaCO(2) (63.8 +/- 21.3 mm Hg vs 47.8 +/- 19.1 mm Hg, p = 0.0101), and lower arterial pH (7.09 +/- 0.12 vs 7.27 +/- 0.12, p < 0.0001), respectively. Patients in 10 of 48 hospital admissions (21%) who required mechanical ventilation died.

CONCLUSIONS

The hospital mortality of patients admitted to an MICU for status asthmaticus is higher than expected. Higher APACHE II score and PaCO(2) and lower arterial pH within 24 h of hospital admission are associated with increased mortality. Sepsis and nonpulmonary organ failure are more likely to develop in nonsurvivors than survivors.

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.

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.

The ventilator: selection of mechanical ventilators

A comprehensive ventilator selection process can be a time-consuming and an overwhelming task. The needs assessment becomes the primary driving tool in the design of the selection process. From the needs assessment, the evaluation can be planned and organized according to the facility requirements, time constraints, and resources. The strategy can expand to an extensive project or have a succinct and condensed design. The needs assessment determines the criteria for the selection, whether it be cost, ventilator specifications, educational needs, manufacturer support needs, maintenance requirements, accessory items, or combinations of any item. Once the data have been collected, it must be analyzed and critiqued. How this examination is performed can be expansive or scaled down according to the facility's resources. Important items in the selection must be maintained and used more extensively in the decision, whereas less important items take a backseat in the operation. The final selection comes from the culmination of the entire process.

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.

Control of ventilation during lung volume changes and permissive hypercapnia in dogs

We investigated the effect changes in end-expiratory lung volume (EEVL) had on the response to progressive hypercapnia (CO2-response curve) in eight open-chest, anesthetized dogs, in order to clarify the role that vagal lung mechanoreceptors have in altered respiratory drive during permissive hypercapnia. The dogs were ventilated using a positive-pressure ventilator driven by phrenic neural activity. Systemic arterial CO2 tension (PaCO2) was elevated by increasing the fraction of CO2 delivered to the ventilator. EEVL was altered from approximated functional residual capacity ("FRC") to 1.5 and 0.5 "FRC" by changing positive end-expiratory pressure. Although the tidal volume (VT)-PaCO2 and inspiratory time (TI)-PaCO2 relationships were not affected, decreasing EEVL from 1.5 "FRC" to "FRC" and then to 0.5 "FRC" caused a significant (p < 0.01) upward shift in the CO2-response curves for minute ventilation (V I) and frequency (f ), and a significant (p < 0.01) downward shift in the CO2- response curve for expiratory time (TE). We conclude that these shifts were explained by a decrease in the inhibitory activity of slowly adapting pulmonary stretch receptors (PSRs) as EEVL was lowered. In addition, increases in EEVL from 0.5 "FRC" to 1.5 "FRC" caused a significant (p < 0.05) increase in the apneic threshold, which we attribute to an inhibitory effect on central drive caused by increased PSR activity.

Severe acute asthma in a community hospital pediatric intensive care unit: a ten years' experience

BACKGROUND

The clinical literature on the incidence and subsequent mortality of asthma has come primarily from the experiences of large tertiary referral centers, particularly in Western Europe and North America. Consequently, very little has been published on the incidence, management, and outcome of asthma in smaller, community-based intensive care units.

OBJECTIVES

The purpose of this study was to explore the course and outcome of children with acute severe asthma treated within a community hospital PICU compared with those described in the literature from larger tertiary referral centers.

DESIGN

A retrospective analysis of 49 asthmatic children admitted to the Pediatric Intensive Care Unit (PICU) over a 10-year period was performed.

MEASUREMENTS AND RESULTS

The mean age was 5.2 years (range 2 months to 16 years), and the male:female ratio was 3:1. Duration of symptoms prior to admission to hospital was less than 24 hours in 60.4% of the patients. The majority of patients was not treated with either inhaled or oral steroids before admission. Drugs used in the PICU included nebulized beta2-agonists, theophylline, steroids, intravenous salbutamol, and intravenous isoproterenol. Although a pharmacologic approach was successful in the majority of patients, intubation and mechanical ventilation were necessary for progressive hypercapnea, exhaustion, and cardiorespiratory arrest in 11/49 of these patients. The average stay in the ICU for our patient group was 2.4 days. Intubated patients had a mean average stay of 3.5 days. Two patients had pneumothorax related to positive pressure ventilation, requiring chest tube insertion for drainage. There were no deaths among the 49 patients admitted to our PICU.

CONCLUSIONS

These data show that for acute severe asthma, outcome is comparable in a community PICU to a tertiary referral institution. We conclude that early ICU admission along with close monitoring is important in reducing morbidity and mortality in children with severe asthma.

Status asthmaticus

Despite improved understanding of the pathophysiology and treatment of asthma, significant morbidity and mortality exist for both the pediatric and adult patient. The critical care practitioner must understand the chronic as well as the acute nature of the condition in order to provide effective intervention. This article reviews the epidemiology and pathophysiology of asthma, clinical assessment, management principles, therapeutic modalities, and future approaches to the management of asthma.

Preventing complications of mechanical ventilation: permissive hypercapnia

Research suggests that the forces exerted on the lungs by mechanical ventilators may cause as much damage to the lungs as the original pathologic process. In an attempt to limit additional injury to damaged lungs and improve the morbidity and mortality of patients requiring mechanical ventilation, investigators have proposed a controversial method of ventilatory management, permissive hypercapnia. This method attempts to maintain adequate oxygenation while allowing ventilation to decrease; carbon dioxide increases. The use of permissive hypercapnia is advocated in patients with acute lung injury and status asthmaticus. Ventilating pressures and volumes are lowered, with a resultant lower minute ventilation. Few adverse effects have been noted when this process has occurred gradually. By using permissive hypercapnia from the initiation of mechanical ventilation, it is possible to support the body through the resolution of the disease process while preventing additional lung injury.

Mechanical ventilation in obstructive lung disease

This article reviews selected topics relevant to the use of mechanical ventilation in patients with severe airflow obstruction. Areas discussed include the bedside assessment of respiratory system mechanics, the ventilatory determinants of dynamic pulmonary hyperinflation, the role of controlled hypoventilation with permissive hypercapnia, and the delivery of bronchodilators during mechanical ventilation.

Clinical features, management, and outcome of patients with severe asthma admitted to the intensive care unit

The objective of this study was to retrospectively review the medical records of 38 consecutive admissions to the medical intensive care unit of a tertiary-care university hospital of patients with severe asthma, and to determine the clinical characteristics of these patients, treatment regimens, and ultimate outcome. The 38 patients presented with severe asthma accompanied by hypoxemia, hypercapnia (mean pCO2 of 54.3 +/- 4.5 mm Hg), and decreased peak flow rates (125.5 +/- 12.4 L/min). The patients spent a mean of 60.1 +/- 9.7 hr in the medical intensive care unit. Seventeen of the 38 patients required intubation and mechanical ventilation. Overall, there were no deaths or significant complications. All 38 patients were discharged from the hospital. We conclude that severe, life-threatening asthma can be appropriately managed in the medical intensive care unit with a low incidence of complications and death. Prolonged mechanical ventilation is rarely required and most patients respond while the relatively simple management strategies.