Asthma

22/05/2013 by admin | Respiratory

Asthma

Definition

Asthma is a common chronic inflammatory lung disease of the airways characterised by variable, reversible and recurring symptoms, airflow obstruction and bronchospasm.

Severity Symptom frequency Nighttime symptoms %FEV1 of predicted FEV1 Variability
Intermittent <1 per week 2 per month 80% <20%
Mild persistent >1 per week but <1 per day >2 per month 80% 20–30%
Moderate persistent Daily >1 per week 60–80% >30%
Severe persistent Daily Frequent <60% >30%

 

Incidence

10-15% of population

Total of 300 million worldwide

Who

More common in developed countries = ‘hygiene hypothesis’.

P/c Cough, expiratory wheeze and dyspnoea (nocturnal dyspnoea common), chest tightness, reduced O2 sats, eosinopjillia, mucus plugs, tachycardic/tachypnoeic, reduced breath sounds…

Asthma attack = tachycardia, rhoncus (=course rattling somewhat like snoring caused by bronchila secretions), accessory muscles, intercostals recession, paradoxyical pulse.

Three characteristics:

  1. 1. Airflow limitation – which is usually reversible spontaneously or with treatment
  2. 2. Airway hyperresponsiveness – to a wide range of stimuli
  3. 3. Inflammation of the bronchi – with eosinophils, T lymphocytes and mast cells with associated plasma exudation (=inflammatory), oedema, marked smooth muscle hypertrophy, mucus plugging and epithelial damage.

 

Classification

Divided into:

  1. Extrinsic – implying a definite external cause
    1. o Atopic individuals who show positive skin-prick reactions to common inhalant allergens.
    2. o Childhood asthma is often accompanied by eczema
    3. o Cause of late-onset asthma in adults is sensitisation to chemicals or biological products in the workplace
  2. Intrinsic or cryptogenic – when no causative agent can be identified
    1. o Often starts in middle age

 

Investigations

Respiratory function tests

  1. Measurements of Peak Expiratory Flow (PEF) on waking prior to taking a bronchodilator and before bed after a bronchodilator.
  2. Spirometry is useful, especially in assessing reversibility.

 

Diagnosed by >15% improvement in FEV1 or PEF following the inhalation of a bronchodilator (i.e. REVERSIBLE [labile obstruction]. FIXED IRREVERSIBLE obstruction = COPD).

Aetiology – cause, risk factors

  1. Occupational sensitisers
  2. Cold air/exercise/stress
  3. Atmospheric pollution and irritant dusts, vapours and fumes, animal fur/dander, HDM faeces, pollen, isocyanates (as found in paints and pesticides).
  4. Diet
  5. Drugs
    1. o NSAIDs (particularly aspirin and propionic acid derivatives). Drugs lead to an imbalance in the metabolism of arachidonic acid due to inhibiting of COX pathway.
    2. o Beta-blockers. Inhibition of beta2 receptors lead to bronchoconstriction and airflow limitation in asthmatic patients.

 

Pathophysiology

Complex – ‘weep and sweep’

Varying clinical severity is dependent on interplay between airway inflammation and airway wall remodelling.

Inflammatory component is driven by Th2-type (CD4+) T lymphocytes which facilitate IgE synthesis.

Treatment/management

Drug treatment:

Step PEFR Treatment
1. Occasional symptoms, less frequent than daily 100% predicted As required bronchodilators (salbutamol PRN). If used more than once daily, move to step 2.
2. Daily symptoms <80% predicted Anti-inflammatory drugs. Sodium cromoglicate or low-dose inhaled corticosteroids (beclomethasone OD)

If not controlled, move to step 3

3. Severe symptoms 50-80% predicted (<60% severe) High-dose inhaled corticosteroids up to 2000ug daily
4. Severe symptoms uncontrolled with high-dose inhaled corticosteroids 50-80% predicted Add regular long-acting beta2 agonists (eg salmeterol – s/s – may inc risk of death in asthma?!)
5. Severe symptoms deteriorating <50% predicted Add prednisolone 40mg PO daily
6. Severe symptoms deteriorating in spite of prednisolone <30% predicted Hospital admission

 

Group: SHORT ACTING BETA-2 AGONISTS (increase adrenaline therefore BRONCHODILATE).
Mechanism: Used for mild to moderate symptoms of asthma.

Produce bronchodilation.

Drug Side effects –due to increased sympathetic activity
SALBUTAMOL

TERBUTALINE

Caution in:

  1. Hyperthyroidism
  2. Cardiovascular disease
  3. Arrhythmias (and ectopy)
  4. QT prolongation
  5. Hypertension
  6. tremor

 

 

Group: LONG ACTING RELIEVERS
Mechanism:
Drug Side effects
LONG ACTING BETA2 AGONISTS (LABA’s):

Administered by inhalation.

Add to regular inhaled corticosteroid treatment.

Role in chronic asthma and useful in nocturnal asthma.

SALMETEROL

FORMOTEROL

Caution in:

  1. Hyperthyroidism
  2. Cardiovascular disease
  3. Arrhythmias
  4. QT prolongation
  5. Hypertension

 

Caution in diabetes – risk of ketoacidosis

Side effects:

  1. Fine tremor
  2. Muscle cramps
  3. Palpitations

 

SODIUM CROMOGLICATE

(mast cell stabaliser = reduce histamine release)

Discontinue if eosinophilic pneumonia occurs

  1. Coughing
  2. Transient bronchospasm
  3. Throat irritation

 

LEUKOTRIENE MODIFIERS:

Block effects of cysteinyl leukotrienes .

May be benefit in exercise-induced asthma and in those with concomitant rhinitis.

MONTELUKAST (‘singulair’)

ZAFIRLUKLAST

PRANLUKAST

Rarely Churg-Strauss syndrome is seen in association with taking leukotriene modifiers.

  1. Abdominal pain
  2. Thirst
  3. Hyperkinesia
  4. Headache

 

 

Group: OTHER AGENTS WITH BRONCHODILATOR ACTIVITY
Mechanism: more often reserved for COPD
Drug Side effects
ANTIMUSCARINIC AGENTS:

IPRATROPIUM

OXITROPIUM

Caution:

  1. Benign prostatic hyperplasia
  2. Bladder outflow obstruction
  3. Angle-closure glaucoma

 

Side effects:

  1. Dry mouth

 

THEOPHYLLINE

Used as bronchodilator in asthma and stable COPD

Metabolised in liver.

Plasma-theophylline concentration is increased in:

  1. Heart failure
  2. Cirrhosis
  3. Viral infections
  4. Elderly

 

Concentration decreased in:

  1. Smokers
  2. Chronic alcoholics
  3. Drugs inducing liver metabolism

 

Toxic dose is close to therapeutic dose (TDM required due to narrow TI)

 

Exacerbations:

Features with acute severe asthma typically have:

  1. Inability to complete a sentence in one breath
  2. RR >25 breaths per minute
  3. Tachycardia >110 bpm
  4. PEF <50% of predicted normal or best

 

Features of life threatening attacks are:

  1. A silent chest, cyanosis or feeble respiratory effect
  2. Exhaustion, confusion or coma
  3. Bradycardia or hypotension
  4. PEF <30% of predicted normal or best

 

Management regimens:

Under-5’s:

  1. SA-BD (beta-2 agonist: salbutamol PRN)inhaled steroid (beclomethasone 200-400mcg/d)leukotriene receptor agonist (monteleukast)refer to respiratory doctors

 

5-12 years old:

  1. SA-BDinhaled steroid (beclomethasone 200-400mcg/d)Long acting beta-2 agonist (LABA: salmeterol)leukotriene (monteleukast) or theothyllineinhaled steroid (beclomethasone 800mcg/d)additional daily oral steroid (prednisolone)refer to respiratory doctors

 

Adults:

  1. SA-BDinhaled steroid (beclomethasone 200-800mcg/d)Long acting beta-2 agonist (LABA: salmeterol)leukotriene (monteleukast) or theothyllineinhaled steroid (beclomethasone up to 2000mcg/d)additional daily oral steroid (prednisolone)refer to respiratory doctors 
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