• Information
  1. Definition
  2. Risk Factors for Life-Threatening Asthma (Table 3)
  3. Initial Treatment
  4. Mechanical Ventilation
  5. Heliox Therapy

A. Definition

1. Respiratory arrest with asthma
2. Fails to clear with usual treatment
3. Requires intubation and mechanical ventillation
4. Underlying bronchitis and/or pneumonia may be present
5. Picornavirus or adenovirus infection may trigger severe asthma attacks [2]

B. Risk Factors for Life-Threatening Asthma (Table 3, Ref [3])

1. Long duration and/or poor control of asthma
2. Dependence on systemic glucocorticoids
3. Noncompliance with medications
4. Psychosocial factors
5. Poor socioeconomic conditions
6. Inconsistent medical followup
7. Delayed medical care
8. Older age
9. Cigarette smoking
10. Aspirin sensitivity
11. Prior hospitalization for asthma
12. Prior use of mechanical ventilation

C. Initial Treatment

1. Components of severe asthma therapy
   1. Oxygen
   2. ß2-adrenergic agonist therapy - nebulized, subcutaneous (SC) or intravenous (IV)
   3. Epinephrine (non-specific adrenergic activity) - SC or IV
   4. Methylprednisolone - 125mg IV bolus then 60-80mg IV q6-8° (children 1-1.5mg/kg IV)
   5. Antibiotics - potential benefits may outweigh risks (consider cefuroxime 750mg IV q8°)
   6. Intubation
   7. Aminophylline
2. ß2-Agonist Therapy
   1. ß2-agonist nebulization every 15-20 minutes
   2. Albuterol, metoproteranol, salbutamol are typically used
   3. Nebulized albuterol 5.0mg q40 minutes is preferred to 2.5mg q20 minutes [4]
   4. Severe asthma impedes entrance of nebulized drug to small airways
   5. Intravenous salbutamol in children reduced hospital stay and oxygen requirements [5]
   6. Epinephrine - usually for patients <40yrs, no history CAD. Initial dose 0.3cc 1:1000 sc.
   7. Consider adjunctive ipatropium bromide (Atrovent®) nebulizer (0.5mg in 3cc saline)
3. Intubation and Mechanical Ventilation
   1. Usual indication: failed response to usual therapies (see below)
   2. Usually requires paralysis or at least sedation; set FiO2 100%
   3. If it requires paralysis, set low tidal volumes and low respiratory rates
   4. This allows for exhalation of delivered breaths, reduced barotrauma (high pressures)
4. Aminophylline
   1. Generally recommended for severe asthma, especially when epinephrine cannot be used
   2. Load with 4-6mg/kg iv then drip 0.4-0.6mg/kg/hr
   3. Levels should be maintained 8-12µg/ml range, never >15µg/ml of serum
   4. There is no added benefit at >15µg/ml range and side effects are severe
5. Other Bronchodilators
   1. Epinephrine - 0.3mL SC q20 minutes x 3 doses maximum; patients <30-35 years of age
   2. Terbutaline - may be used in pediatric cases, given SC or IV
   3. Isoproterenol - in very difficult cases with resistant disease, IV at 0.1mg/minute

D. Mechanical Ventilation

1. Indications
   1. Respiratory rate increasing to >40 breaths per minute
   2. Peak flows decreasing with patient fatigue
   3. Rising PaCO2 and/or falling pH despite therapies
2. Paralysis and sedation are often required
   1. Atracurium (curare derivative) may be used
   2. Vecuronium / Pavulon may lead to post-paralytic myopathy in up to 70% of patients
   3. Curare is relatively contraindicated due to increased histamine release
   4. Sedation with fentanyl, morphine, ± lorazepam or diazepam or midazolam
   5. Propofol may have bronchodilating effects and can be used for sedation
3. AC or IMV Modes with initial tidal volumes 7-8cc/kg (as low as 5 cc/kg)
4. High intrathoracic pressures and autopeep may lead to hypotension
   1. Support with generous IV fluids
   2. Up to 1 liter/hour
   3. Because of the poor venous return due to high intrathoracic pressures, patients require high intravascular volumes to maintain blood pressure
5. Peak Inspiratory Pressure (PIP) typically ~90 cm
   1. Generally, these high PIPs are expected and not concerning
   2. PIPs should be used to follow improvement
   3. Plateau pressures should be normal
6. Maintain plateau pressure <20cm
7. Follow arterial blood gases (ABGs) for correction of acidosis
   1. Typically, initial ABG on 100% FiO2: pH 7.03, pO2 114, pCO2 92
   2. Acidosis should be corrected with bicarbonate to maintain pH > 7.25
   3. A HCO3- drip may be needed
8. Weaning should only be attempted when PIPs
   1. Follow ventillator pressures
   2. Sedation may be lightened
   3. Diuretics may be used to improve compliance (especially if high volumes given initially)
   4. Acetazolamide (Diamox®; eg. 500mg iv qd) can decrease HCO3- and maintain pH

E. Heliox Therapy [1,6]

1. Heliox is a blend of oxygen and helium with lower density and higher viscosity than air
2. Inhalation of heliox converts turbulent flow in some bronchospastic airways to laminar
3. Reduces the resistive work of breathing, unloads respiratory muscles
4. Reverses hypercapnea in some patients with severe status asthmaticus
5. Composed of 60-80% helium with oxygen mixed
6. Use restricted to trained personell

References

1. Manthous CA. 1995. Am J Med. 99(3):298
2. Tan WC, Xiang X, Qiu D, et al. 2003. Am J Med. 115(4):272
3. Wechsler ME, Shepard JO, Mark EJ. 2007. NEJM. 356(20):2083 (Case Record)
4. McFadden ER Jr, Strauss L, Hejal R, et al. 1998. Am J Med. 105(1):12
5. Browne GJ, Penna AS, Phung X, Soo M. 1997. Lancet. 349:301
6. Kass JE and Castriotta RJ. 1995. Chest. 107:757