Diagnosis of Asthma

Asthma symptoms include:

intermittent dyspnoea
Chest tightness or pain
Trouble sleeping by SOB, coughing or wheezing
Audible whistling or wheezing sound when exhaling
Bouts of coughing or wheezin worsened by a respiratory virus eg. cold/flu
acid reflux: known association with asthma

Getting worse..
An increase in the severity and frequency of above
A fall in peak flow rates as measured by a peak flow meter
An increased need to use bronchodilators — medications that open up airways by relaxing the surrounding muscles

Signs:
tachypnoea
audible wheeze
hyperinflated chest
hyperresonant percussion
diminished air entry
widespread polyphonic wheeze

Severe attack:
inability to complete statements, pulse >110bpm, respiraory rate >25.min, PEF 33-50% of predicted

Life-threatening attack:
silent chest, cyanosis, bradycardia, exhaustion, PEF <33% of predicted, confusion, feeble respiratory effort

Diagnosis

Acute:

PEF (peak expiratory flow)
sputum culture
FBC (full blood count)
U&E (Urea & electrolyte)
CRP (C-reactive protein)
blood cultures
ABG (arterial blood gas) analysis shows normal or slightly reduced PaO2 and low PaCO2 (hyperventilation)
[if PaCO2 is raised, transfer to high dependency unit for ventilation, as this shows failing respiratory effort]
CXR (to exclude infection or pneumothorax)

Chronic:

PEF monitoring
diurnal variation of >20% on >3 days a week for 2 weeks
spirometry
obstrucive defect (decrease FEV1/FVC, increase RV)
CXR:hyperinflation

skin-prick test: allergens identification

PEF
- >20% difference on >3days in a week for 2 weeks (marked morning dipping common)
- >20% improvement following treatment
- >20% decrease following exposure to trigger

Based on clinical history & exam: eczema, allergic conditions, family history

IN CHILDREN:
Unable to use airway f(x) test. Medical history and improvement shown with an inhaled bronchodilator medication.

NEW: Chemical marker of Exhaled NO. Higher levels of NO = higher severity of asthma (expensive though..)

DDx

pulmonary oedema ('cardiac asthma')
COPD (often coexist)
large airway obstruction (foreign body/tumour)
SVC obstruction (wheeze/dyspnoea not episodic)
pneumothorax
PE
bronchiectasis
obliterative bronchiolitis (in elderly)

Source: mayoclinic, oxford handbook of clinical medicine