Acute asthma exacerbation

Background

• 3 questions
  • 1. Does this pt have asthma?
    • Most wheezing in pt <3yr is not asthma
  • 2. What is the severity?
  • 3. Is there a treatable preciptant?

Diagnosis

• Dyspnea, wheezing, and cough
• Prolonged expiration
• Accessory muscle use
• Sign of impending ventilatory failure
  • Paradoxical respiration
    • Chest deflation and abdominal protrusion during inspriation
  • Altered mental status
  • "Silent chest"

DDX

1. CHF ("cardiac asthma")
2. Upper airway obstruction
3. Aspiration of foreign body or gastric acid
4. Bronchogenic carcinoma with endobronchial obstruction
5. Metastatic carcinoma with lymphangitic metastasis
6. Sarcoidosis with endobronchial obstruction
7. Vocal cord dysfunction
8. Multiple pulmonary emboli (rare)

Work-Up

Consider CXR if:

1. Fever > 102.2
2. Worsening sx
3. Poor response to Rx
4. 1st wheeze

Treatment

1. Albuterol
   1. Nebulizer
      1. 2.5-5mg q20min x3, then 2.5-10mg q1-4hr as needed OR
      2. Continuous = 0.15mg/kg/hr (max 25mg/hr)
   2. MDI
      1. 4-8 puffs q20min up to 4h, then q1-4hr as needed
2. Ipratropium
   1. 0.5mg q20min x3
3. Steroids
   1. Dexamethasone
      1. As effective as prednisone
      2. 0.6mg/kg IV or PO (max 16mg); 2nd dose 24hr later
   2. Prednisone
      1. 40-60mg/day in one or two divided doses x5d
   3. Methylprednisolone
   4. 1mg/kg IV q 4–6hr
   5. Only use IV if cannot tolerate PO
4. Magnesium
   1. 1-2gm IV over 30min
   2. Duration of action approx 20min
5. Epinephrine
   1. 1:1000 0.01mg/kg (max 0.5mg) subQ Q20min x 3 OR
6. Terbutaline
   1. 0.25mg subQ q20min x 3
      • Caution in elderly/CHF
7. Heliox
8. Ketamine
9. Non-invasive Ventilation
   1. Consider as alternative to intubation
   2. Alleviates muscle fatigue which leads to larger tidal volumes
   3. Maximize inspiratory support
      1. Inspiratory pressure 8
      2. PEEP 0-3
10. Intubation
    1. Consider induction w/ ketamine
    2. Ventilation of asthmatic pts requires deep sedation
       1. Benzos, propfol, or ketamine (1mg/kg/hr)
    3. Settings
       1. Assist-control ventilation
       2. Resp rate
          1. Start slow to avoid air-trapping
          2. RR ~ 10
          3. Make sure plateau pressure <30
             1. If >30 must lower resp rate
          4. May require "permissive hypoventilation"
             1. Low peak pressure/avoidance of breath stacking more important than correcting CO2
       3. Tidal volume 8cc/kg ideal wt
       4. PEEP 0
       5. Flow rate 80
    4. Use bronchodilators even when intubated

Disposition

• Dispo based in part on peak flow
  • Predicted = (30 x age (yrs)) + 30
  • Discharge if symptoms resolved and PEF >70% predicted
  • Admit if symptoms persist and PEF <40% predicted
  • Discharge versus admit based on physician judgment if some symptoms persist, PEF 40-69% predicted

See Also

Ventilator Desaturation

Source

• Rosen's
• Tintinalli
• EMcrit Podcast 15