assessment of severity of acute asthma

Classification

Clinical stages of asthma:

stage	paO2	pCO2	pH
Stage 1	paO2 > 80 mm Hg	pCO2 < 35 mm Hg	pH > 7.45
Stage 2	paO2 60-80 mm Hg	pCO2 < 35 mm Hg	pH > 7.45
Stage 3	paO2 < 60 mm Hg	pCO2 35-40 mm Hg	pH > 7.35-7.45
Stage 4	paO2 < 60 mm Hg	pCO2 35-40 mm Hg	pH < 7.35
Stage 5	paO2 < 60 mm Hg	pCO2 > 45 mm Hg	pH < 7.35

Stage 1 & 2 mild, stage 3 moderate, stage 4 & 5 severe asthma. Increased CO2 reflects lactic acidosis related to increased work of breathing

Management

• Indications of severity include:
  • previous need for mechanical ventilation
  • respiratory distress at rest
  • difficulty speaking in full sentences
  • diaphoresis
  • use of accessory respiratory muscles
  • respiratory rate > 28/min
  • pulsus paradoxus > 10 mm Hg
  • subcutaneous emphysema associated with pneumothorax or pneumomediastinum
  • respiratory fatigue
• Laboratory data supporting a need for hospitalization:
  • Spirometry:
    • FEV1 < 30% of predicted value initially, or < 40% with 1 hour of therapy
    • peak flow < 60 L/min or < 50% of predicted value after 1 hour of therapy
  • Arterial blood gas:
    • PaO2 < 60 mm Hg
    • normal or increased CO2 may be a sign of impending respiratory arrest
• Signs of severe asthma
  • impaired pulmonary function
    • FEV1 < 1.0 L
    • PEFR < 80 L/min
  • hypoxemia (paO2 < 60 mm Hg)
  • hypercarbia (pCO2 > 45 mm Hg) & acidosis (pH < 7.35)
  • change in mental status
    • agitation
    • confusion
    • lethargy
    • exhaustion
  • atrial or ventricular arrhythmias
  • pulsus paradoxus > 20 mm Hg
  • pneumothorax
• Criteria for admission to hospital
  • emergency visit within the past 3 days
  • failure of subjective improvement following treatment
  • failure of FEV1 to increase by > 500 mL or absolute value < 1.6 L
  • failure of post-treatment peak expiratory flow rate (PEFR) to increase more than 15% above initial value or absolute value < 200 L/min
  • change in mental status
    • lethargy
    • agitation
    • exhaustion
    • confusion
  • failure of hypercarbia to improve after treatment
  • presence of pneumothorax

More general terms

• symptom assessment