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: 1) 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 2) Laboratory data supporting a need for hospitalization: a) 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 b) Arterial blood gas: - PaO₂ < 60 mm Hg - normal or increased CO₂ may be a sign of impending respiratory arrest 3) Signs of severe asthma a) impaired pulmonary function - FEV1 < 1.0 L - PEFR < 80 L/min b) hypoxemia (paO₂ < 60 mm Hg) c) hypercarbia (pCO₂ > 45 mm Hg) & acidosis (pH < 7.35) d) change in mental status - agitation - confusion - lethargy - exhaustion e) atrial or ventricular arrhythmias f) pulsus paradoxus > 20 mm Hg g) pneumothorax 4) Criteria for admission to hospital a) emergency visit within the past 3 days b) failure of subjective improvement following treatment c) failure of FEV1 to increase by > 500 mL or absolute value < 1.6 L d) failure of post-treatment peak expiratory flow rate (PEFR) to increase more than 15% above initial value or absolute value < 200 L/min e) change in mental status - lethargy - agitation - exhaustion - confusion f) failure of hypercarbia to improve after treatment g) presence of pneumothorax

References

Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998