Question

What is the pathophysiological mechanisms of chronic and acute asthma exacerbation. Explain the changes in arterial blood gas patterns

Answer 1

Asthma is a chronic inflammatory disorder of the airways.

Asthma is diffuse, chronic inflammatory disease of large and small airways punctuated by acute exacerbations of airflow obstruction which are at least partially reversible.

*In asthma exacerbation patients that "can't get a deep breath" during an acute attack usually sit upright or slightly bent forward using the accessory muscles of respiration to get enough air.

The more difficult the breathing becomes, the more anxious the patient feels.

*Chronic / Severe and life-threatening asthma exacerbations can occur when the is at rest and the patient speaks in words, not sentences because of the difficulty in breathing and perspire profusely. They become drowsy and confused as the ABG's deteriorate, breath sounds are difficult to hear and there is no wheezing present. Accessory muscles in the neck are straining to lift the chest wall, and the patient is often agitated. Neck vein distention may result.

Acute asthma exacerbation is the acute or sub-acute episode of :

*Progressively worsening shortness of breath

*Cough

*Wheezing

*Chest tightness

#Asthma exacerbation pathophysiology by allergic triggers:

Allergens such as pet dander, dust mites, and pollen $\rightarrow$ Inflammation of airways  $\rightarrow$ may exacerbate the airflow obstruction

#Asthma exacerbation pathophysiology by non-specific triggers:

Nonspecific stimuli such as smoke, exercise and chemical spray $\rightarrow$ irritation of airways $\rightarrow$ exacerbation of airflow obstruction  

#Asthma exacerbation pathophysiology by infection triggers :

Infections such as viral, bacterial and fungal infections $\rightarrow$ inflammation of airways $\rightarrow$ may exacerbate the airflow obstruction

#Asthma exacerbation pathophysiology by mast cell action :

In early stages :

Mast cells in airway mucosa release mediators such as histamine, leukotrienes, platelet activating factor $\rightarrow$ biphasic immune response $\rightarrow$ bronchoconstriction  $\rightarrow$ airflow obstruction

In late stages : (begins 6-8 hours later)

Hypersecretion of mucus, airway edema, epithelial desquamation, and infiltration of inflammatory cells.

#Asthma exacerbation pathophysiology by airway obstruction :

Airway obstruction with nonuniform ventilation and atelectasis leads to ventilation/perfusion (V/Q) mismatch.

Hyperinflation leads to decreased compliance and increased work of breathing.

Increased intra-thoracic pressure impairs venous return and reduces cardiac output

*Asthma exacerbation with a family history of asthma may exacerbate.

# Asthma exacerbation is diagnosed by ABG"S :

ABG is considered obtaining if there is a concern for respiratory insufficiency/failure

For acute exacerbation elevated pH with low PCO2 and normal or low pO2 (respiratory alkalosis)

In severe exacerbation PaCO2 is high or sometimes normal, ie 5-6kPa and PaO2 is <8kPa with or without administration of oxygen with low pH