Block 3: asthma, COPD, PE Flashcards
Asthma definition
Asthma is a chronicrespiratorycondition characterized by recurrent episodes of airflow obstruction, bronchial hyperresponsiveness, and underlying inflammation.
Asthma pathophysiology
- Driven by Th2 inflammation (eosinophils, lymphocytes and mast cells)
- 1/4 of asthma is non-eosinophilic and driven by neutrophils. Less steroid responsive and harder to treat
- Airway obstruction develops through smooth muscle constriction, mucosal infiltration and mucous hyper-secretion
- Eventually remodelling can develop causing loss of reversibility in chronic asthma
- Eczema, seasonal allergic rhinitis and nasal polyps are often associated with high IgE and asthma
- Sinusitis, reflux and obstructive sleep apnoea can all worsen asthma control
Asthma risk factors
- Genetics
- Environmental: allergens (pollen, dust), respiratory infection, tobacco smoke and air pollution
- Immunological factors: imbalance in immune response particularly type 2 helper cells
- personal or family history ofatopy
- antenatal factors: maternal smoking, viral infection during pregnancy (especially RSV)
- low birth weight
- not being breastfed
- maternal smoking around child
Atopy and occupational asthma
Atopy: IgE mediated conditions i.e. atopic dermatitis (eczema) and allergic rhinitis (hay fever)
Occupational asthmais usually diagnosed by observing reduced peak flows during the working week with normal readings when not at work. Examples of common occupational allergens include isocyanates and flour. Ask if their symptoms are better on holiday or at the weekend
Asthma physical changes
- A chronic inflammatory of the airways secondary to type 1 hypersensitivity
- Causes reversible bronchospasm resulting in airway obstruction
- Airway inflammation: causes oedema, mucus production and bronchoconstriction
- Bronchoconstriction: contraction of airway smooth muscle due to histamine and leukotrienes
- Airway hyperresponsiveness: narrowing in response to allergens, irritants and cold air
- Mucus production and airway remodelling: changes include subepithelial fibrosis, increased smooth muscle mass, mucus gland hypertrophy, and angiogenesis. Airway remodelling can cause irreversible airflow obstruction and progressive decline in lung function, may not be entirely reversible
Asthma: clinical features
- Wheeze: high pitched whistling sound that occurs in expiration
- Cough: worse at night/early morning
- Chest tightness
Asthma testing patients >= 17 years
- patients should be asked if their symptoms are better on days away from work/during holidays. If so, patients should be referred to a specialist as possible occupational asthma
- all patients should have spirometry with a bronchodilator reversibility (BDR) test
- all patients should have a FeNO test
Asthma testing children 5-16 years and <5 years
- all children should have spirometry with a bronchodilator reversibility (BDR) test
- a FeNO test should be requested if there is normal spirometry or[obstructive spirometry]with a negative bronchodilator reversibility (BDR) test
<5 years: on clinical judgement, cant be confirmed till >5
Tests available for asthma: FeNO and spirometry
- FeNO= in adults level of >= 40 parts per billion (ppb) is considered positive. In children a level of >= 35 parts per billion (ppb) is considered positive
- Spirometry= FEV1/FVC ratio less than 70% (or below the lower limit of normal if this value is available) is considered obstructive
Testing available for asthma: reversibility and peak flow monitoring
- Reversibility testing in response to nebulised salbutamol (spirometry)= in adults, a positive test is indicated by an improvement in FEV1 of 12% or more and increase in volume of 200 ml or more. In children, a positive test is indicated by an improvement in FEV1 of 12% or more
- Peak flow monitoring (2-4 weeks can be useful), variability in peak flow of 20% suggests asthma
Asthma treatment in adults
- Newly diagnosed asthma: SABA (salbutamol)
- SABA + low dose ICS (400mg) (beclometasone)
- SABA + low dose ICS + leukotriene receptor antagonist (LTRA) (montelukast)
- SABA + low dose ICS + LABA (salmeterol). Continue LTRA depending on patients response
- SABA +/- LTRA. Switch ICS/LABA for a maintenance and reliever therapy (MART) that includes a low dose ICS
- SABA +/- LTRA + medium dose ICS MART. OR consider changing to fixed dose of moderate ICS and a separate LABA
Asthma: maintenance and reliever therapy (MART)
- a form of combined ICS and LABA treatment in which a single inhaler, containing both ICS and a fast-acting LABA, is used for both daily maintenance therapy and the relief of symptoms as required
- MART is only available for ICS and LABA combinations in which the LABA has a fast-acting component (for example, formoterol)
Asthma: dosage of ICS
- <= 400 micrograms budesonide or equivalent = low dose
- 400 micrograms - 800 micrograms budesonide or equivalent = moderate dose
- > 800 micrograms budesonide or equivalent= high dose.
Moderate acute asthma exacerbation
- Increasing symptoms.
- PEFR >50-75% of the patient’s best or predicted score.
- No features of acute severe asthma.
Acute severe asthma exacerbation
- PEFR 33-50% of the patient’s best or predicted score.
- Respiratory rate (RR) ≥ 25 breaths per minute.
- Heart rate (HR) ≥ 110 beats per minute.
- Inability to complete sentences in one breath.
Life threatening asthma exacerbation
- PEFR <33% of the patient’s best or predicted score.
- SpO₂ <92%, PaCO2 is normal
- PaO₂ <8kPa.
- Absence of audible breath sounds over the chest (silent chest).
- Cyanosis (usually of the lips), hypotension
- Reduced respiratory effort, exhaustion
- New-onset arrhythmia.
- Reduced Glasgow coma score (GCS).
Near fatal asthma exacerbation
Raised PaCO₂ (>6kPa) and/or need for mechanical ventilation.
Acute asthma exacerbation
- Can be unprovoked or provoked by viruses, bacteria, allergens like mould or tobacco smoke
- Tend to develop in less than 6 hours with worsening of breathlessness, cough, wheeze and chest tightness
- Things that suggest increased severity: tachypnoea, tachycardia, inability to speak in full sentences, silent chest
Acute asthma exacerbation: investigations
- PEFR and FEV1 assess severity, PEFR is expressed as a percentage of the patients best or predicted score
- SpO2: drop to <92% suggests its life threatening
- Arterial blood gas (ABG): indicated if the patient’s SpO₂ is <92% or PEFR is ≤30% of best or predicted. Hypercapnia (PaCO₂ >6kPa) suggests that a patient’s attack is near-fatal. Most patients will have respiratory alkalosis in severe cases with hypercapnia they have metabolic acidosis
- Venous blood gas: less useful