Author:
Melissa H.White
TylerGiberson
Description
- Increased expiratory resistance:
- Airway inflammation
- Bronchospasm
- Mucosal edema
- Mucous plugging
- Smooth muscle hypertrophy
- Consequences:
- Air trapping
- Airway remodeling
- Increased dead space
- Hyperinflation
- Status asthmaticus refers to disease that does not respond to therapy within 30-60 min
- Risk factors for life-threatening disease:
- Prior intubations
- Intensive care unit admissions
- Chronic steroid use
- Hospital admission for asthma during the past year
- Inadequate medical management
- Increasing age
- Ethnicity (African Americans)
- Lack of access to medical care
- Multiple comorbidities
Etiology
- Inflammatory process of the airways evidenced by episodic and reversible airflow obstruction and hyperresponsiveness with many cells and cellular elements contributing to the disease:
- Neutrophils
- Mast cells
- Eosinophils
- Macrophages
- T-lymphocytes
- Epithelial cells
- Cytokines
- Triggers:
- Pollen
- Dust mites
- Molds
- Animal dand er
- Other environmental allergens
- Viral upper respiratory infections
- Occupational chemicals
- Tobacco smoke
- Environmental change
- Cold air
- Exercise induced
- Emotional factors
- Menstrual associated
- Drugs:
Signs and Symptoms
- Wheezing
- Dyspnea
- Chest tightness
- Cough
- Tachypnea
- Tachycardia
- Respiratory distress:
- Posture sitting upright or leaning forward
- Use of accessory muscles
- Inability to speak in full sentences
- Diaphoresis
- Poor air movement
- Impending failure:
- Altered mental status
- Worsening fatigue
- Paradoxical respiration
- Pulsus paradoxus >18 mm Hg
Essential Workup
- Primarily a clinical diagnosis
- Measure and follow severity with peak expiratory flow rate (PEFR)
- Assess for underlying disease
Diagnostic Tests & Interpretation
Lab
- Arterial blood gas:
- Not helpful during the initial evaluation
- The decision to intubate should be based on clinical criteria
- Mild-moderate asthma: Respiratory alkalosis
- Severe airflow obstruction and fatigue: Respiratory acidosis and PaCO2 >42
- Pulse oximetry:
- <90% is indicative of severe respiratory distress
- Patients with impending respiratory compromise may still maintain saturation above 90% until sudden collapse
- WBC:
- Leukocytosis is nonspecific
- Pneumonia
- Chronic steroid use
- Stress of an asthma exacerbation
- Demargination occurs after administration of epinephrine and steroids
Diagnostic Procedures/Surgery
- PEFR:
- Estimates the degree of airflow obstruction:
- Normal peak flow (adult) is 400-600
- 100-300 indicates moderate airway obstruction
- <100 is indicative of severe airway obstruction
- Use serially as an objective measure of the response to therapy
- Forced expiratory volume (FEV):
- More reliable measure of lung function than PEFR
- Difficult to use as a screening tool
- Often unavailable in the ED
- Severe airway obstruction: FEV1<30-50%
- CXR:
- Indications:
- Fever
- Suspicion of pneumonia
- Suspicion of pneumothorax or pneumomediastinum
- Foreign body aspiration
- First episode of asthma
- Comorbid illness: e.g., diabetes, renal failure, CHF, AIDS, cancer
- Not responding to treatment
- Typical findings:
- Hyperinflation
- Scattered atelectasis
- ECG:
- Indicated in patients at risk for cardiac disease:
- Dysrhythmias
- Myocardial ischemia
- Transient changes in severe asthma:
- Right axis deviation
- Right bundle branch block
- Abnormal P-waves
- Nonspecific ST-T-wave changes
Differential Diagnosis
- Allergic reaction
- Angioedema
- Bronchiolitis
- Bronchitis
- Carcinoid tumors
- Chemical pneumonitis
- Chronic cor pulmonale
- Chronic obstructive pulmonary disease
- CHF
- Croup
- Foreign body aspiration
- Immersion injury
- Myocardial ischemia
- Pneumonia
- Pulmonary embolus
- Smoke inhalation
- Upper airway obstruction
- Venous air embolus
Prehospital
- Recognize the “quiet chest” as respiratory distress
- Supplemental oxygen
- Continuous nebulized β-agonist/anticholinergics
- Administration of IM/SC epinephrine
- Administration of corticosteroids
Initial Stabilization/Therapy
- Immediate initiation of inhaled β-agonist treatment
- Intubate for fatigue and respiratory distress
- Steroids (if not given by EMS)
ED Treatment/Procedures
- Oxygen:
- Maintain an oxygen saturation >90%
- β-Adrenergic agonist:
- Selective β2-agonists (albuterol)
- Mild-moderate asthmatic: Administer every 20 min
- Severe asthmatic: Continuous nebulized treatment
- SC β-agonist (terbutaline and epinephrine):
- Suspected allergic reaction
- Severe exacerbations
- Limited inhalation of aerosolized medicine
- More side effects because of systemic absorption
- Terbutaline - longer-acting β2 agonist with bronchodilating effects equivalent to epinephrine in acute asthma
- Relative contraindication: Age >40 yr and coronary disease
- Corticosteroids:
- Reduce airway wall inflammation
- Administered early
- Onset of action may take 4-6 hr
- Administer IV/PO
- IV methylprednisolone (Solu-Medrol) in the treatment of severe asthma exacerbation
- Mild-moderate exacerbations may be treated with oral prednisone burst or methylprednisolone acetate (Depo-Medrol) IM
- Solu-Medrol is quick but short acting (hours) and Depo-Medrol is slow, but long acting (days)
- Inhaled corticosteroids are currently not recommended as initial therapy
- Anticholinergic agents:
- If minimal response to initial β-agonist treatment
- Severe airflow obstruction
- Inhaled anticholinergic agents should be used in conjunction with β-agonists
- Magnesium sulfate:
- May have a benefit in severe asthma
- No benefit in mild-moderate asthma
- Aminophylline:
- Rare utility in acute management
- May be of benefit if patient previously maintained on theophylline/aminophylline
- Leukotriene inhibitors:
- May be useful in setting of asthma triggered by aspirin or other NSAID
- Not recommended for routine use
- Heliox:
- Mixture of helium and oxygen (80:20, 70:30, 60:40)
- Decreased density may improve delivery to bronchospastic lungs
- Decrease airway resistance
- Decrease in respiratory exhaustion
- Not currently recommended for routine use
- Consider in severe asthma
- Noninvasive positive pressure ventilation:
- CPAP and BiPAP
- May improve oxygenation and decrease respiratory fatigue
- Can only be used in an alert patient
- Should not replace intubation
- May force nebulized treatments deeper into airways
- Not currently recommended for routine use
- Consider in severe asthma
- Ketamine:
- Bronchodilator and an anesthetic agent
- Useful as an induction agent during intubation
- Use with caution in patients with CAD, CHF, HTN
- Halothane:
- Inhalation anesthetics are potent bronchodilators
- Refractory asthma in intubated patients
- Intubation of the asthmatic patient:
- Rapid sequence intubation
- Can consider lidocaine to attenuate airway reflexes
- Ketamine is preferred as induction agent
- Propofol also thought to have bronchodilatory properties but should be used with caution as it will cause hypotension
- Etomidate can be used if contraindication to ketamine/propofol
- Succinylcholine should be administered to achieve paralysis
- A large endotracheal tube >7 mm should be used to facilitate ventilation
- May need to mechanically exhale for the patient
- Permissive hypercapnia
Medication
- β-agonists:
- Albuterol: 2.5 mg in 2.5 mL NS q20min inhaled (peds: 0.1-0.15 mg/kg/dose q20min [min dose 1.25 mg])
- Epinephrine: Adult: 0.3 mg (1:1,000) SC q0.5-4h × 3 doses (peds: 0.01 mg/kg up to 0.3 mg SC)
- Terbutaline: 0.25 mg SC q0.5h × 2 doses (peds: 0.01 mg/kg up to 0.3 mg SC)
- Corticosteroids:
- Methylprednisolone: 60-125 mg IV (peds: 1-2 mg/kg/dose IV/PO q6h × 24 hr)
- Prednisone: 40-60 mg PO (peds: 1-2 mg/kg/d in single or divided doses)
- Depo-Medrol: 160 mg IM
- Anticholinergics:
- Magnesium: 2 g IV over 20 min (peds: 25-75 mg/kg)
- Aminophylline: 0.6 mg/kg/hr IV infusion
- Rapid sequence intubation:
- Ketamine: 1-1.5 mg/kg IV, propofol: 2 mg/kg IV, or etomidate: 0.3 mg/kg IV
- Lidocaine: 1-1.5 mg/kg IV
- Succinylcholine: 1.5 mg/kg IV
Disposition
Admission Criteria
Medical Wards
Medical Wards- PEFR <40% and minimal air movement
- Persistent respiratory distress:
- Factors that should favor admission:
- Prior intubation
- Recent ED visit
- Multiple ED visits or hospitalizations
- Symptoms for more than 1 wk
- Failure of outpatient therapy
- Use of steroids
- Inadequate follow-up mechanisms
- Psychiatric illness
Medical Wards
Observation Unit- PEFR >40% but <70% of predicted
- Patients without subjective improvement
- Patients with continued wheeze and diminished air movement
- Patients with moderate response to therapy and no respiratory distress
Discharge Criteria
- PEFR >70% should be >300
- Patient reports subjective improvement
- Clear lungs with good air movement
- Adequate follow-up within 48-72 hr
Follow-up Recommendations
Encourage patients to contact their PMD or pulmonologist for asthma-related problems over the next 3-5 d
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- National Asthma Education and Prevention Program Expert Panel Report 3. Guidelines for Diagnosis and Management of Asthma. US Dept of Health and Human Services; 2007.
The authors gratefully acknowledge Carolyn Maher Overman for her contribution to the previous edition of this chapter.