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ASTHMA-Etiology, Pathogenesis, Clinical Presentation, Diagnosis & Treatment!

 ASTHMA

Definition:

According to WHO:

"It is a disease characterized by recurring attacks of breathlessness and wheezing which vary in frequency according to the nature of allergen and these symptoms vary from hour to hour or day to day".

According to Principle & Practice of Medicines by Davidson:

"It is chronic inflammatory disorder of airways associated with airway hyper-responsiveness that leads to recurrent episodes of wheezing, breathlessness or coughing particularly at night or early in the morning".

Etiology:

  • Hyperresponsiveness-exaggerated response of airway to any non-specific stimulus which results in airway obstruction.
  • Broncho-constriction- Breathlessness or spasm due to construction of bronchioles in airway stimulus.


Allergens:

  1. Industrial chemicals such as paints, hairsprays or resins
  2. Drugs such as NSAIDs, Beta-blockers
  3. Food products such as dairy products, fish, etc.
  4. Environmental pollutants such as cigarette, smoke
  5. Industrial triggers such as wood
  6. Miscellaneous


Pathophysiology:

  • Hypersensitivity Type-1
  • Atopy- genetic tendency
  • Allergy
  • Platelet activating factors (PAF)

  1. Extrinsic allergens (common in children) or Intrinsic non-allergens (triggered by non-allergen factors such as excessive exercise or other factors except allergens, cause inflammation due to either presence of eosinophils or absence of eosinophils.
  2. Mast cells release antibodies as a result of IgE immediate response (Histamine, Prostaglandin generating factors, Bradykinin, Macrophages, Platelet Activating factors (PAF)

*The PAF are produced by the macrophages which cause hyper-responsiveness and release plasma into bronchial cavity leading to hypertrophy*.

       3. Mucosal cells increase mucosal secretion resulting in wheezing, hypercapnia (CO2 not being exhaled).

Clinical Presentation

  • persistent cough (Most common symptom)
  • Difficulty breathing associated with wheezing.
  • Increased pulse rate (110beats/min)
  • Heart rate (90 beats/min)
  • PFR 100L/min
  • Saturated oxygen level is reduced to < 92%
  • Hypercapnia (increased C02)
*Arterial Blood Gas test (ABG) detects all these changes*.


Investigation

FEV1: 

Force Expiratory volume in 1 second. This is used for the measurement of exhalation (how much we exhale in 1 second)

FVC:

Force Vital Capacity Detects maximum exhalation. Spirometer is used for this purpose.

FEV/FVC ratio should always be greater than 0.7%




Peak Flow Meter (PF Meter): 

This apparatus can be used by the patient itself at home. It checks the flow rate and also the prognosis i.e, either asthma is controlled or not.


Diagnosis:

  • Global Initiative for Asthma control (GINA) states that the diagnosis of asthma can be confirmed with response to bronchodilators and examine the patient variation in peak expiration rate (PEFR) day to day. If there is a diagonal (24hr) variability of 60L/min or more than 20% is highly suggestive for asthma diagnosis.


Treatment:

  • Treatment for chronic asthma according to BTS/SIGN Guidelines include Reliever ( SABA) and Controller/Preventer (Steroids)
  1. Inhale reliever as required (2-4 puffs repeated every 4hrs).
  2. Patient took reliever and is not recovered, so the patient is moved to controllers. Dose recommended is 200-800microgram/day to 400microgram/day. Start the dose of Inhaled Corticosteroids (ICS) according to severity.
  3. Additional add-on therapy:
  • Add LABA. Inhale long acting B2 agonist.
  • Now access the response. If good response, continue. If benefits from LABA but control is still inadequate, continue LABA but increase dose up to 800mg/day. (If not use the same dose).
  • If no response to LABA, stop LABA and increase the dose of ICS. Use the trial of other drugs or sustain release theophylline or leukotriene.
  • Persistent poor control. Increase the dose of ICS upto 200microgram/day and addition of the 4th drug b2 agonist (Salbutamol orally).
  • Continuous or frequently use of oral corticosteroids (OCS). Use daily steroid tablets in lowest dose. Maintain high dose of ICS (200 microgram/day). Consider other tablets to minimize use of steroid tablets.
  • Specialized care to the patients.

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