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"

Differential Diagnosis

Acute dyspnea

Emergent

• Pulmonary
  • Airway obstruction
  • Anaphylaxis
  • Angioedema
  • Aspiration
  • Asthma
  • Cor pulmonale
  • Inhalation exposure
  • Noncardiogenic pulmonary edema
  • Pneumonia
  • Pneumocystis Pneumonia (PCP)
  • Pulmonary embolism
  • Pulmonary hypertension
  • Tension pneumothorax
  • Idiopathic pulmonary fibrosis acute exacerbation
  • Cystic fibrosis exacerbation
• Cardiac
  • Cardiac tamponade
  • Cardiogenic pulmonary edema (CHF)
  • Myocardial Infarction
  • Pericarditis
  • Myocarditis
• Other Associated with Normal/↑ Respiratory Effort
  • Abdominal distension
  • Anemia
  • CO Poisoning
  • Salicylate toxicity
  • Diabetic ketoacidosis (DKA)
  • Diaphragm injury
  • Electrolyte abnormalities
  • Epiglottitis
  • Flail chest
  • Hypotension
  • Metabolic acidosis
  • Pneumonia
  • Pneumothorax/hemothorax
  • Renal Failure
  • Sepsis
  • Toxic ingestion
• Other Associated with ↓ Respiratory Effort
  • Guillain-Barre syndrome
  • Multiple sclerosis
  • Myasthenia Gravis
  • Lambert-Eaton Syndrome
  • Organophosphate toxicity
  • Stroke (Main)
  • Tick paralysis

Non-Emergent

• ALS
• Ascites
• Uncorrected ASD
• Congenital heart disease
• COPD exacerbation
• Fever
• Hyperventilation
• Interstitial lung disease
• Neoplasm
• Obesity
• Panic attack
• Pleural effusion
• Polymyositis
• Porphyria
• Pregnancy
• Rib fracture
• Spontaneous pneumothorax
• Thyroid Disease
• URI

Work-Up

Consider CXR if:

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

Treatment

Albuterol

Favor continuous nebulization to decrease the chance of admission when compared to intermittent dosing

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

Ipratropium

1. 0.5mg q20min x3

Steroids

Should be given in the first hour with effects to reduce admission

1. Dexamethasone
   1. As effective as prednisone especially in children
   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
   1. 1mg/kg IV q 4–6hr
   2. Only use IV if cannot tolerate PO since equal effectiveness between dosing routes

Magnesium

1. 1-2gm IV over 30min
2. Duration of action approx 20 min
3. In patients with moderate to severe asthma there is a decreased rate of admission with an NNT of 2
4. Epinephrine
   1. 1:1000 0.01mg/kg (max 0.5mg) subQ or IM Q20min x 3

Terbutaline

• Longer-acting beta2-agonist promoting bronchodilation

1. 1. 0.25mg subQ q20min x 3
      • Caution in elderly/CHF

Heliox

• 60 to 80% helium is blended with 20 to 40% oxygen
• Heliox improves non laminar flow and may increases the diffusion of carbon dioxide by improving ventilation

Ketamine

• Provides bronchodilation and sedation however it does promote secretions
• Ketamine is the preferred induction agent for intubation in an asthmatic.
• Dosing 1-2mg/kg

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

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
   3. Start slow to avoid air-trapping
   4. RR ~ 10
   5. Make sure plateau pressure <30
   6. If >30 must lower resp rate
   7. May require "permissive hypoventilation"
      1. Low peak pressure/avoidance of breath stacking more important than correcting CO2
   8. Tidal volume 8cc/kg ideal wt
   9. PEEP 0
   10. Flow rate 80
4. Use bronchodilators even when intubated

Disposition

• A short course of glucocorticoids (prednisone in adults or dexamethasone in children (0.6mg/kg) decreases change of relapse
• Although classically disposition is based on peak flow measurements such results are often not available in the ED
  • 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 and adequate home support

See Also

Ventilator Desaturation