eMedicine Specialties > Emergency Medicine > Pulmonary

Asthma: Differential Diagnoses & Workup

Author: Barry E Brenner, MD, PhD, FACEP, Professor of Emergency Medicine, Professor of Internal Medicine, Program Director, Emergency Medicine, University Hospitals, Case Medical Center
Contributor Information and Disclosures

Updated: Jul 2, 2009

Differential Diagnoses

Chronic Obstructive Pulmonary Disease and Emphysema

Other Problems to Be Considered

Anaphylaxis (adult, pediatric)
Bronchiolitis (pediatric)
Foreign body ingestion (pediatric, adult incompetent, neurologically impaired)
Polyarteritis nodosa
Adrenal insufficiency if steroids stopped too abruptly
Congestive heart failure and myocarditis
Pulmonary embolism (especially multiple)
Upper airway disease
Panic disorder and hyperventilation syndrome
Pneumonia, bronchitis
Paradoxic vocal cord dysfunction

Workup

Laboratory Studies

  • Laboratory studies are not indicated for most ED patients with acute asthma, and they should not delay treatment for someone in respiratory distress.
  • The white blood cell (WBC) count may be elevated if the patient is taking prednisone, has received catecholamines (ie, epinephrine), or has been under significant stress.
  • Eosinophilia may be helpful in diagnosing asthma in a patient with new-onset wheezing and bronchospasm reversible with beta2-agonists.
  • Although potassium may be diminished with beta2-agonist treatment, this hypokalemia rarely produces any clinically significant effects.
  • Serum theophylline levels are helpful in monitoring patient compliance and excluding inadvertent theophylline toxicity.
  • Arterial blood gas
    • Arterial blood gas (ABG) measurement provides important information in acute asthma. This test may reveal dangerous levels of hypoxemia or hypercarbia secondary to hypoventilation; typically, results are consistent with respiratory alkalosis.
    • Because of the accuracy and utility of pulse oximetry, only patients whose oxygenation is not restored to over 90% with oxygen therapy require an ABG. The clinical picture usually obviates ABGs for most ED patients with acute asthma.
    • Venous levels of PCO2 have been tested as a substitute for arterial measurements, and a venous PCO2 of >45 mm may serve as a screening test but cannot substitute for the ABG evaluation of respiratory function.
    • Hypercarbia is of concern in that it reflects inadequate ventilation and may indicate the need for mechanical ventilation if the PCO2 is elevated as a result of patient exhaustion; however, the decision to proceed with endotracheal intubation and mechanical ventilation is a clinical assessment.

Imaging Studies

  • Chest radiography
    • Chest radiography of patients with acute asthma rarely reveals clinically significant findings, although it may show streaky infiltrates or hyperinflation of the lung fields. It may be helpful in suggesting the diagnosis of asthma in the ED or in unclear causes of dyspnea.
    • Patients with pleuritic chest pain require a chest film to exclude pneumothorax or pneumomediastinum, particularly if subcutaneous emphysema is present.
    • Chest radiography is indicated in those with fever to rule out pneumonia. Acute sinusitis may exacerbate asthma, and sinus radiograph results are frequently positive in patients who have acute asthma and a fever. However, the nonspecificity of sinus films should temper enthusiasm for this imaging study.
    • With new-onset asthma and eosinophilia, a radiograph may be useful in identifying prominent streaky infiltrates persisting less than 1 month, indicating Loeffler pneumonia. The infiltrates of Loeffler pneumonia are peripheral with central sparing of the lung fields. These findings have been described as the radiographic negative of pulmonary edema.

Other Tests

  • Electrocardiogram and ECG monitoring
    • Patients with asthma who are severely symptomatic should have ECG monitoring, as with any seriously ill patient.
    • Sinus tachycardia and ECG evidence of right heart strain are common in patients with acute asthma. The use of beta2-agonist therapy will cause a paradoxical decrease in heart rate as pulmonary function improves and symptoms are relieved.
    • Supraventricular tachycardia raises the consideration of theophylline toxicity.
    • Arrhythmias, other than supraventricular tachycardia, are rare.
  • Pulse oximetry
    • Pulse oximetry measurement is desirable in all patients with acute asthma to exclude hypoxemia. The hypoxemia of uncomplicated acute asthma is readily reversible by oxygen administration. Oxygenation decreases 4-10 mm Hg with beta-agonist inhalant therapy due to increases in V/Q mismatch. Therefore, all patients with acute asthma should have oxygen saturation measured by pulse oximetry, or they simply should be placed on oxygen therapy.
    • In children, pulse oximetry is often used to grade severity of acute asthma. Oxygen saturation of 97% or above constitutes mild asthma, 92-97% constitutes moderate asthma, and less than 92% signifies severe asthma. Although an isolated pulse oximetry reading at triage is not predictive in most cases (with the notable exception of severe attacks that usually are self-evident on visual inspection), serial monitoring of pulse oximetry status can provide more subtle evidence for or against the need for hospital admission.
  • Spirometry provides a physiologic assessment of airflow and degree of bronchospasm. It gives a more objective assessment of the level of bronchospasm than subjective findings of dyspnea and degree of wheezing. Although valuable in adults, obtaining accurate values in the emergency setting is often difficult (or impossible) among most children younger than 6 years.
    • Peak expiratory flow (PEF) measurement is common in the ED because it is inexpensive and portable. Serial measurements document response to therapy and, along with other parameters, are helpful in determining whether to admit the patient to the hospital or discharge from the ED. A limitation of PEF is that it is dependent on effort by the patient. Forced expiratory volume in one second (FEV1) is also effort dependent but less so than PEF. FEV1 is not often used in the ED except in research settings.
    • PEF in the ED can be compared with asymptomatic (baseline) PEF, if known. Unfortunately, patients often do not know their asymptomatic PEF. Moreover, the reference group for the ideal PEF percent predicted (based on age, sex, height) may not be accurate for the patient population seen in many inner city EDs since most equations are based on white populations.

More on Asthma

Overview: Asthma
Differential Diagnoses & Workup: Asthma
Treatment & Medication: Asthma
Follow-up: Asthma
References
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Further Reading

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Keywords

asthma, asthma attack, asthma symptoms, asthma treatment, asthma evaluation, asthma assessment, asthma causes, airway obstruction, asthma management, asthma exacerbation, airway inflammation, bronchial asthma, asthma triggers, dyspnea, wheezing, shortness of breath, asthmatic, reactive airway disease, wheeze, bronchiolitis, acute asthma, asthma prevention, allergies, bronchial airways, bronchial airway narrowing, inflammation of the bronchi, bronchial smooth muscle contraction, airway narrowing, noisy breathing, difficult breathing, difficulty breathing, inhalers, lung disease

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Contributor Information and Disclosures

Author

Barry E Brenner, MD, PhD, FACEP, Professor of Emergency Medicine, Professor of Internal Medicine, Program Director, Emergency Medicine, University Hospitals, Case Medical Center
Barry E Brenner, MD, PhD, FACEP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Chest Physicians, American College of Emergency Physicians, American College of Physicians, American Heart Association, American Thoracic Society, Arkansas Medical Society, New York Academy of Medicine, New York Academy of Sciences, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Medical Editor

Edward Bessman, MD, Chairman, Department of Emergency Medicine, John Hopkins Bayview Medical Center; Assistant Professor, Department of Emergency Medicine, Johns Hopkins University
Edward Bessman, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Paul Blackburn, DO, FACOEP, FACEP, Program Director, Department of Emergency Medicine, Maricopa Medical Center; Assistant Professor, Department of Surgery, University of Arizona
Paul Blackburn, DO, FACOEP, FACEP is a member of the following medical societies: American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, American Medical Association, and Arizona Medical Association
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Robert E O'Connor, MD, MPH, Professor and Chair, Department of Emergency Medicine, University of Virginia Health System
Robert E O'Connor, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Physician Executives, American Heart Association, American Medical Association, Medical Society of Delaware, National Association of EMS Physicians, Society for Academic Emergency Medicine, and Wilderness Medical Society
Disclosure: Nothing to disclose.

 
 
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