Assure adequate oxygenation for asthmatic patients receiving albuterol

Assure adequate oxygenation for asthmatic patients receiving albuterol: Excerpt from Avoiding Common Pediatric Errors

Author: Madan Dharmar, MD

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Asthma is a condition where airway hyperresponsiveness due to a chronic inflammatory condition of the lung airways results in episodic airflow obstruction.Theseepisodesofairflowobstructioncanpresentwithmildsymptoms, such as dry coughing, expiratory wheezing, chest tightness, dyspnea; or severe symptoms, such as respiratory distress, hypoxic seizures, respiratory failure, and even death. There is no definitive cause for asthma, but an interplay of genetic and environmental causes seems likely. Nearly 80% of asthmatics report an onset of asthma before the age of 6 and not all children with recurrent wheeze develop persistent asthma in later childhood. A history of parental asthma, allergies in childhood, severe lower respiratory tract infection, wheezing apart from colds, low birth weight, male gender, and environmental tobacco smoke exposure are considered to be important risk factors for persistent asthma.

The National Asthma Education and Prevention Program classifies asthma based on four parameters: (a) frequency of daytime symptoms, (b) nighttime symptoms,(c)degree of airflowobstructionbyspirometry, and/or (d) peak expiratory flow variability. According to this classification, asthmatics can be categorized in four disease severity groups, as "mild intermittent," "persistent mild," "persistent moderate," and "persistent severe." The goal of asthma management is to reduce airway inflammation by the use of daily "controller" anti-inflammatory medications, minimize exposure to proinflammatory environmental exposures, and controlling comorbid conditions that can worsen asthma.

When exacerbations do occur, early intervention using systemic glucocorticoids and β-agonist bronchodilators can reduce the severity of these episodes. The mild intermittent asthma is the only group where a daily anti-inflammatory (controller) is not used and the β-agonist bronchodilators (reliever) is used for all levels of severity groups. Pharmacotherapy in the management of asthma can be divided into quick-relief medication and long-term control medication. Quick-relief medications are used to manage acute episodes of bronchospasm, which include inhaled β2-agonistss (e.g., albuterol), inhaled anticholinergics (e.g., ipratropium), and short-course systemic glucocorticoids (e.g., prednisone). Long-term control medications are used to manage mild-to-moderate persistent asthma, which include nonsteroidal anti-inflammatory agents (e.g., cromolyn), inhaled glucocorticoids (e.g., beclomethasone), sustained-release theophylline, long-acting inhaled β-agonists (e.g., salmeterol), and leukotriene modifiers (e.g., montelukast).

The Role of β-agonist Bronchodilators and Oxygen in Acute Severe Asthma. In acute asthma exacerbation, there is narrowing of the airway. This is caused by in airway inflammation, resulting in mucosal edema and hypersecretion, and airway obstruction due to bronchospasm. The body's homeostatic response is to decrease the blood flow to underventilated lung units. By this mechanism, the body maximizes oxygenation by matching pulmonary perfusion with alveolar ventilation. In acute severe asthma, the pattern of ventilation-perfusion is bimodal, ranging from normally perfused to areas of hypoxic pulmonary vasoconstriction.

In acute severe exacerbation of asthma, the management includes correction of hypoxemia, rapid improvement of airflow obstruction, and prevention of progression or recurrence of symptoms. Children admitted to the hospital for acute severe exacerbations of asthma are treated with supplemental oxygen, frequently administered β2-agonistss, and systemic glucocorticoids. Inhaled β2-agonistss are considered the first line of medication to treat acute asthma exacerbation. Treatment with inhaled β2-agonistss is often given to relieve bronchospasm and improve oxygenation.

In acute severe asthma, nebulization of β2-agonistss without oxygen can cause or worsen hypoxemia. The β2-agonistss can alter the homeostatic response by causing pulmonary vasodilatation and increasing perfusion to poorly ventilated lung units, resulting in ventilation perfusion mismatch and causing more hypoxemia. Hypoxia perpetuates bronchoconstriction, which further worsens the condition of the child. This mechanism was initially seen in isoproterenol, a β-agonist that was commonly used for asthma. It has also been found that salbutamol can worsen ventilation-perfusion mismatch by similar mechanism of pulmonary vasodilatation and increasing cardiac output.

Suggested Readings

Field GB. The effects of posture, oxygen, isoproterenol and atropine on ventilation-perfusion relationships in the lung in asthma. Clin Sci. 1967;32(2):279–288.
Harris L. Comparison of the effect on blood gases, ventilation, and perfusion of isoproterenol- phenylephrine and salbutamol aerosols in chronic bronchitis with asthma. J Allergy Clin Immunol. 1972;49(2):63–71.
Inwald D, Roland M, Kuitert L, et al. Oxygen treatment for acute severe asthma. BMJ. 2001;323(7304):98–100.

Book Source Details

• Book Title: Avoiding Common Pediatric Errors
• Author(s): Anthony D Slonim MD, DrPH; Lisa Marcucci MD
• Year of Publication: 2008
• Copyright Details: Avoiding Common Pediatric Errors, Copyright © 2008 Lippincott Williams & Wilkins.

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• Back to disease: Asthma: Introduction
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: Avoiding Common Pediatric Errors Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7489-6

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