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🌟 Asthma

 🎯 Pathology​

  • an inflammatory condition that affects the airways characterised by airway hyper-responsiveness to specific triggers and episodic airway limitation caused by bronchospasms (contraction of airway smooth muscle cells)

 💡 Causes​

  • the exact aetiology is known, although it is associated with other atopic conditions including eczema, allergic rhinitis (hay fever) and food allergies

  • triggers

    • infection

    • drugs: aspirin, beta-blockers, adenosine

    • occupational: isocyanates

    • exercise

    • animal dander

    • dust

    • cigarette smoke

🩺 Clinical features​

  • symptoms

    • dyspnoea

    • chest tightness

  • signs

    • wheeze

    • increased accessory muscle use

    • prolonged expiration

    • severe asthma causes pulsus paradoxus (fall in systolic blood pressure more than 10 mm Hg during inspiration)

  • Aspirin-exacerbated respiratory disease (Samter’s triad of asthma)

    • a triad of: nasal polyps + sensitivity to aspirin or NSAIDs + chronic rhinosinusitis

    • it is NOT an IgE-mediated reaction

🕵️‍♂️ Investigations

  • spirometry

    • obstructive pattern: FEV1/FVC ratio < 70%

  • reversibility testing

    • involves repeating spirometry testing following the administration of a short-acting beta-2 agonist

    • improvement in FEV1 by ≥ 12% or increase by ≥ 200 ml in volume = positive result

  • fractional exhaled nitric oxide (FeNO)

    • shows how much nitric oxide is exhaled with each breath

    • nitric oxide is a marker of inflammation

    • ≥ 40 parts per billion = positive result

  • peak flow variability

    • recorded over 2-4 weeks

    • variability by ≥ 20% = positive result

  • methacholine challenge

    • methacholine is used to induce bronchoconstriction

    • decrease in FEV1 by ≥ 20% = positive result

  • arterial blood gas (ABG)

    • respiratory alkalosis in acute asthma exacerbation due to hyperventilation

  • chest x-ray

    • may be normal or demonstrate hyperinflation

💆‍♂️ Management (BTS/SIGN 2019) guidelines

  • 1st line

    • short-acting beta-2 agonist (SABA) e.g. salbutamol

    • this is known as reliever therapy

  • 2nd line

    • add low dose inhaled corticosteroids (ICS)

  • 3rd line

    • add long-acting beta-2 agonist (LABA) e.g. salbutamol/formoterol

    • ICS and LABA are combined in one inhaler (brown inhaler) also known as maintenance and reliever therapy (MART) e.g. Symbicort/Fostair

  • 4th line

    • add leukotriene receptor antagonist (LTRA) e.g. montelukast, or

    • increase ICS to a medium dose

  • 5th line

    • refer to specialist

😢 Acute asthma exacerbation

Clinical features​

  • not responding to reliever therapy

  • worsening shortness of breath

  • wheeze

  • may be preceded by a respiratory infection

Severity

  • moderate

    • peak expiratory flow rate 50-75% best or predicted

  • severe

    • peak expiratory flow rate 33-50% best or predicted

    • respiratory rate > 25

    • heart rate > 110

    • cannot complete sentences

  • life-threatening (”33-92-CHEST”)

    • peak expiratory flow rate 33% best or predicted

    • SpO2 < 92%

    • Confusion

    • Hypotension

    • Exhaustion

    • Silent chest

    • Tachycardia

  • near-fatal

    • raised PaCO2 which is is indicative of exhaustion

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Management

  • immediate management

    • ​back-to-back nebulisers with oxygen

      • salbutamol

      • ipratropium (if unresponsive to salbutamol, severe or life-threatening)

    • prednisolone or hydrocortisone

  • additional therapy requiring specialist input

    • magnesium sulfate

    • theophylline

    • mechanical ventilation

​

Criteria for discharge

  • FEV1 and/or PEF should be > 75% best or predicted

  • SpO2 > 94%

  • install a personalised asthma action plan

  • inhaler technique must be checked

  • arrange follow-up

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