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Diseases of Airway Obstruction : Asthma

November 07, 2010 Edit this post

Definition chronic, generally variable inflammatory disorder of the airways resulting in episodes of reversible hyper-responsive inf...

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Definition

  • chronic, generally variable inflammatory disorder of the airways resulting in episodes of reversible hyper-responsive inflammation and bronchospasm causing airflow obstruction
  • paroxysmal or persistent symptoms such as dyspnea, chest tightness, wheezing, sputum production and/or cough
  • associated with reversible airflow limitation and airway hyper-responsiveness to endogenous or exogenous stimuli



Epidemiology

  • common (7-10% of adults), especially in children (10-15%)
  • most children with asthma improve significantly in adolescence
  • often family history of atopy (asthma, allergic rhinitis, eczema)
  • occupational asthma



Etiology and Pathophysiology

  • acute asthma: airway obstruction ---> V/Q mismatch ---> hypoxemia ---> increased ventilation ---> decreased PaCO2 ---> increased pH and muscle fatigue ---> decreased ventilation, increased PaCO2/decreased pH



Triggers

  • URTIs, allergens (pet dander, house dusts, molds), irritants (cigarette smoke, air pollution), drugs (NSAIDs, beta-blockers), preservatives (sulphites, MSG), other (emotion/anxiety, cold air, exercise, GERD)

    Signs and SymptomsParty smile


    • tachypnea, wheezing, chest tightness, cough (especially nocturnal), sputum production


    Important Signs and Symptoms

    Red Flags

    Respiratory Distress

    fatigue

    diminished expiratory effort

    cyanosis  

    silent chest

    decreased LOC

    nasal flaring, tracheal tug

    inability to speak

    accessory muscle use, intercostal indrawing

    pulsus paradoxus

     

    Risk Factors Indicating Poor Asthma Control

    Previous Non-Fatal Episodes

    Ominous Signs and Symptoms

    loss of consciousness during asthma attack

    frequent ER visits

    prior intubation  

    ICU admission

    night time symptoms >1 night/week  

    silent chest

    FEV1 or PEF (peak expiratory flow) <60%

    limited activities of daily living

    use of beta2 agonists >3 times/day

    Criteria for determining whether asthma is well controlled

    1. daytime symptoms <4 days/wk
    2. no asthma-related absence from work/school
    3. night-time symptoms, <1 night/wk         
    4. beta-2 agonist use <4 times/wk
    5. normal physical activity
    6. FEV1 or PEF >90% of personal best
    7. mild, infrequent exacerbations
    8. PEF diurnal variation <10-15%

      Investigations

      • O2 saturation
      • ABGs
        • decreased PaO2 during attack (V/Q mismatch)
        • decreased PaCO2 in mild asthma due to hyperventilation
        • normal or increased PaCO2 ominous as patient is no longer able to hyperventilate (worsened airway obstruction or respiratory muscle fatigue)
      • PFTs (may not be possible during severe attack, do when stable)
        • spirometry: increase in FEV1 >12% with beta2-agonist, or >20% with 10-14 days of steroids, or >20% spontaneous variability
        • provocation testing: decrease in FEV1 >20% with methacholine challenge


      TreatmentPrincess

      • environmental control: avoid relevant triggers
      • patient education: features of the disease, goals of treatment, self-monitoring
      • pharmacological therapy:
        • symptomatic relief in acute episodes: short-acting beta2-agonist, anticholinergic bronchodilators, oral steroids, addition of a long acting beta2-agonist
        • long-term prevention of acute episodes: inhaled/oral corticosteroids, anti-allergic agent, long-acting beta2-agonist, methylxanthine, leukotriene receptor antagonists (LTRA)

      Clinical PearlOpen-mouthed smile

      Central cyanosis is not detectable until the SaO2 is <85%.
      It is more easily detected in polycythemia and less readily detectable in anemia.

      Asthma Triad

      asthma
      ASA/NSAID sensitivity
      nasal polyps

      Guidelines for Asthma Management

      image

      Eemergency Management of Asthma

      1. inhaled beta2-agonist first line (MDI route and spacer device recommended)
      2. add anticholinergic therapy
      3. ketamine and succinylcholine for rapid sequence intubation in life-threatening cases
      4. SC/IV adrenaline, IV salbutamol if unresponsive
      5. all patients admitted to ER for asthma exacerbations should be considered for corticosteroid therapy at discharge

       

      Clinical PearlOpen-mouthed smile

      Remember to step down therapy to lowest doses which control symptoms/signs of bronchoconstriction.

       
      Medical Mnemonics Freezing

       

       

      Beta-1 vs Beta-2 receptor location

      "You have 1 heart and 2 lungs":
      Beta-1 are therefore primarily on heart.
      Beta-2 primarily on lungs.

       

       

      Zafirlukast, Montelukast, Cinalukast: mechanism, usage

      "Zafir-luk-ast, Monte-luk-ast, Cina-luk-ast":
      · Anti-Lukotrienes for Asthma.
      · Dazzle your oral examiner: Zafirlukast antagonizes leukotriene-4.

       

       

      Asthma drugs: leukotriene inhibitor action

      zAfirlukast: Antagonist of lipoxygenase
      zIlueton: Inhibitor of LT receptor

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