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CPAP and Asthma

Question# 870

Why is asthma listed as a contraindication for CPAP?

I understand how it may not be the first thing to reach for in an asthma exacerbation, however more often than not I hear about older patients getting CPAP withheld because the medic was informed of a history of asthma alongside a diagnosis of COPD. The hard contraindication as opposed to a clinical consideration makes it awkward to justify putting the CPAP on these patients to support their ventilation in these mixed cases.

I also understand that in some Canadian paramedic services asthma is a specific indication for CPAP, and many of these pure asthma patients I have brought in (or see getting brought in) get placed on CPAP by respiratory therapy in order to help avoid needing the BVM and especially intubation.

Thanks for the help on clarifying the tools exclusion in these patients.

Answer:

Asthma and chronic obstructive pulmonary disease (COPD) are both respiratory conditions that affect airflow, but they differ in their underlying pathophysiology, which impacts the use of therapies like CPAP (Continuous Positive Airway Pressure) and NIV (Noninvasive Ventilation).

Asthma involves reversible airway inflammation and bronchoconstriction, leading to airflow obstruction, especially during an attack. During an asthma exacerbation, the airways constrict and become inflamed, making it difficult for air to flow in and out of the lungs. The concern with CPAP in asthma lies in its potential to worsen these symptoms. Increased pressure from CPAP could further narrow the already-constricted airways, making it harder for air to flow. Moreover, the airway narrowing from bronchospasm combined with CPAP's continuous positive pressure can cause air to accumulate, or "stack," in the lungs. This creates difficulty with exhalation, as the lungs are inflated but struggle to expel the air, worsening respiratory distress. In addition, because asthmatic patients often have a slower expiratory rate, CPAP can contribute to overinflation and barotrauma, further damaging the lungs. As such, CPAP is generally contraindicated in asthma, especially during an acute exacerbation. Having said that, the directive speaks to a contraindication of an asthma exacerbation. A patient with a history of asthma can still benefit from CPAP therapy.

Conversely, COPD involves progressive, irreversible airway damage, often due to emphysema and chronic bronchitis. In these patients, CPAP is typically beneficial for several reasons. COPD results in a loss of lung elasticity, which can cause airway collapse. CPAP helps keep the airways open, preventing this collapse and improving overall oxygenation and ventilation. Unlike asthma, where the lung tissue is usually normal and the obstruction is primarily in the airways, the damaged, "floppy" lungs in COPD are more tolerant of the positive pressure from CPAP, reducing the risk of barotrauma.

Noninvasive ventilation (NIV) such as BiPAP (Bilevel Positive Airway Pressure) is commonly used for patients with COPD, especially during acute exacerbations, to improve ventilation and reduce hypercapnia (high CO2 levels). BiPAP's dual pressure system, where higher pressure is applied during inhalation and lower pressure during exhalation, helps improve alveolar ventilation, decreases the work of breathing, and improves gas exchange. However, in asthma, the role of NIV is less clear. Though NIV, especially BiPAP, can help reduce respiratory distress and prevent invasive intubation in severe asthma exacerbations, the evidence for its benefit is limited. Some studies suggest that it may reduce the need for invasive ventilation in cooperative patients who are not yet in respiratory failure, but overall data on its efficacy in asthma is not as strong as in COPD.

The use of NIV in asthma is still being studied, and while it may offer temporary relief in certain cases, it should be considered with caution. Noninvasive ventilation might be appropriate for patients who are experiencing severe, persistent exacerbations despite maximal bronchodilator therapy but do not require immediate intubation. In these patients, NIV can reduce the work of breathing, decrease airway resistance, and help re-expand collapsed alveoli, potentially avoiding the need for invasive mechanical ventilation.

In summary, CPAP is generally contraindicated in asthma due to the risk of worsening airway narrowing, air stacking, and barotrauma. In contrast, CPAP and NIV can be beneficial in COPD, where the lungs are already structurally damaged and better tolerate positive pressure. NIV, particularly BiPAP, is increasingly used in patients with severe asthma exacerbations, but its role is still evolving, and it should be carefully considered, particularly for patients not on the verge of respiratory failure.

References


UpToDate

- Acute exacerbations of asthma in adults: emergency department and inpatient management
- An overview of asthma management in children and adults
- Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications
- Airway management in acute severe asthma for emergency medicine and critical care
- Acute severe asthma exacerbations in children and adolescents: Endotracheal intubation and mechanical ventilation
- Invasive mechanical ventilation in adults with acute exacerbations of asthma

Published

31 January 2025

ALSPCS Version

5.3

Views

77

Please reference the MOST RECENT ALS PCS for updates and changes to these directives.