eMedicine Specialties > Pulmonology > Obstructive Airways Diseases

Status Asthmaticus: Differential Diagnoses & Workup

Author: Constantine Saadeh, MD, Chief, Department of Internal Medicine, Northwest Texas Hospital; President, Allergy ARTS, LLP; Clinical Professor, Departments of Internal Medicine, Pediatrics, Microbiology, and Immunology, Texas Tech Health Science Center
Contributor Information and Disclosures

Updated: Jun 4, 2009

Differential Diagnoses

Pulmonary Hypertension, Primary

Other Problems to Be Considered

Congestive heart failure
Croup
Stridor
Upper airway obstruction
Orthopnea

Workup

Laboratory Studies

• Obtain a CBC count and differential to evaluate for infectious causes (eg, pneumonia, viral infections such as croup), allergic bronchopulmonary aspergillosis, and Churg-Strauss vasculitis. As noted earlier, when elevated, serum lactate levels (when obtained early at the onset of status asthmaticus) can correlate with improved lung function.
• Obtain an arterial blood gas (ABG) value to assess the severity of the asthma attack and to substantiate the need for more intensive care. ABG determinations are indicated when the peak expiratory flow (PEF) rate or forced expiratory volume in one second (FEV₁) is less than or equal to 30% of the predicted value or when the patient shows evidence of fatigue or progressive airway obstruction despite treatment. ABG values are important to help determine the severity of the asthma attack. The 4 stages of blood gas progression in persons with status asthmaticus are as follows:
  • The first stage is characterized by hyperventilation with a normal partial pressure of oxygen (PO₂).
  • The second stage is characterized by hyperventilation accompanied by hypoxemia (ie, a low partial pressure of carbon dioxide [PCO₂] and low PO₂).
  • The third stage is characterized by the presence of a false-normal PCO₂; ventilation has decreased from the hyperventilation present in the second stage. This is an extremely serious sign of respiratory muscle fatigue that signals the need for more intensive medical care, such as admission to the ICU and, probably, intubation with mechanical ventilation.
  • The last stage is characterized by a low PO₂ and a high PCO₂, which occurs with respiratory muscle insufficiency. This is an even more serious sign that mandates intubation and ventilatory support.

Imaging Studies

• Obtain a chest radiograph to evaluate for pneumonia, pneumothorax, congestive heart failure, and signs of chronic obstructive pulmonary disease, which would complicate the patient's response to treatment or reduce the patient's baseline spirometry values.

Other Tests

• The most important and readily available test to evaluate the severity of an asthma attack is the measurement of PEF. PEF monitors are commonly available to patients for use at home, and they provide patients with asthma with a guideline for changes in lung function as they relate to changes in symptoms. In most patients with asthma, a decrease in peak flow as a percent of predicted value correlates with changes in spirometry values.
• According to the guidelines of the National Heart, Lung, and Blood Institute/National Asthma Education and Prevention Program,⁴ severe asthma exacerbation is usually associated with a PEF rate or FEV₁ of less than 50% of the predicted value. Also, hospitalization is generally indicated when the PEF or FEV₁ after treatment is greater than 50% of the predicted value but less than 70% of the predicted value. Hospitalization in the ICU is indicated when the PEF value or FEV₁ is less than 50% of predicted.
• A drop in the FEV₁ to less than 25% of the predicted value indicates a severe airway obstruction.
• A patient with an FEV₁ of greater than 60% of the predicted value may be treated in an outpatient setting, depending on the clinical situation. However, if the patient's FEV₁ or PEF rate drops to less than 50% of predicted, admission to the hospital is recommended.
• Pulse oximetry and spirometry values should be used to monitor the progression of asthma. As the results indicate improvement, treatment may be adjusted accordingly.
  • If a portable spirometry unit is not available, a PEF rate of 20% or less of the predicted value (ie, usually <100 L/min) suggests severe airflow obstruction and impending respiratory failure.
  • Spahn et al⁵ demonstrate that the majority of children with asthma have normal spirometry results. According to Goldman et al⁶ and Marotta et al,⁷ the assessment of children with asthma is enhanced by the use of forced oscillation to measure respiratory resistance and reactance. As reported by Ducharme and Davis^8,9 in 1997 and 1998, forced oscillation can be performed in the emergency department, and the results are reproducible.
  • According to various articles, impulse oscillometry resistance and reactance magnitudes have been shown to be more sensitive than FEV₁ to the daily variability in adolescents with asthma (Goldman et al⁶ ), to the response to acute bronchodilation (Marotta et al⁷ and Skloot et al¹⁰ ), and to the response to exposure to toxic inhalants in persons with reactive airways (Skloot et al¹⁰ ). In patients with reactive airways, Saadeh et al¹¹ report that impulse oscillometry detects false-negative spirometry values and provides a sensitive index of asthma control over the spectrum of mild-to-severe persistent asthma.

Procedures

• With forced oscillation testing using the impulse oscillometry system (IOS), patients are tested for 30-40 seconds during quiet breathing, without forced respiratory efforts. A small loudspeaker pushes "burps" of air into patients and pulls them back from the mouthpiece 5 times each second.
  • The measurement of airflow resistance during normal breathing requires no maximal forced expiratory efforts and does not subject patients to bronchoprovocation from forced expiration. Resistance is distributed between large airways and smaller more peripheral airways, with distinct patterns attributable to each.
  • Bronchospasms and increased large airway resistance appear as increases in resistance at higher (25-35 cycles/s) components of oscillation frequency. Additionally, a pattern of increased resistance with increasing airflow is typical of a large airway bronchospasm. In such patients, resistance at the beginning and end of both inspiration and expiration is at its minimum, with increased levels during mid inspiration and mid expiration. In such patients, a deep inspiration is often followed by reflex bronchoconstriction and increased resistance for 30 seconds or more, signaling increased airway reactivity.
  • Peripheral airway inflammation and obstruction are signaled by increased resistance at low (5 cycles/s) oscillation frequencies that are decreased at higher oscillation frequencies (15 or 20 cycles/s). In association with the fall in resistance from 5 to 15 cycles per second, the magnitude of respiratory reactance in peripheral airway inflammation and obstruction increases.
  • Careful attention must be paid to whether patients have their lips fully closed around the mouthpiece. Patients with acute dyspnea may feel constrained breathing through a mouthpiece and may reflexively open their mouths to increase airflow during late inspiration. This is analogous to flaring alae nasi with dyspnea and results in characteristic airflow leak patterns. This causes underestimation of true airflow resistance. IOS tests with such airflow leak patterns must be repeated after reassuring the patient and ensuring closure of the lips around the mouthpiece.

Histologic Findings

Autopsy results from patients who died from status asthmaticus of brief duration (ie, developed within hours) show neutrophilic infiltration of the airways. In contrast, results from patients who developed status asthmaticus over days show eosinophilic infiltration. Autopsy results also show extensive mucus production and severe bronchial smooth muscle hypertrophy. However, the predominant response, based on results from bronchoalveolar lavage studies, is eosinophilic in nature. The eosinophil itself can lead to epithelial destruction through its own degrading products (eg, cationic proteins). This destruction can result in inflammation and, later, a neutrophilic response.

Staging

The 4 stages of status asthmaticus are based on ABG progressions in status asthma.

Patients in stage 1 or 2 may be admitted to the hospital, depending on the severity of their dyspnea, their ability to use accessory muscles, and their PEF values or FEV₁ after treatment (>50% but <70% of predicted values).

Patients with ABG determinations characteristic of stages 3 and 4 require admission to the ICU. The PEF value or FEV₁ is less than 50% of the predicted value after treatment.

• Stage 1
  • Patients are not hypoxemic, but they are hyperventilating and have a normal PO₂.
  • Data suggest that to possibly facilitate hospital discharge, these patients may benefit from ipratropium treatment via a handheld nebulizer in the emergency setting as an adjunct to beta-agonists.
• Stage 2
  • This stage is similar to stage 1, but patients are hyperventilating and hypoxemic.
  • Such patients may still be discharged from the emergency department, depending on their response to bronchodilator treatment, but will require systemic corticosteroids.
• Stage 3
  • These patients are generally ill and have a normal PCO₂ due to respiratory muscle fatigue. Their PCO₂ is considered a false-normal value and is a very serious sign of fatigue that signals a need for expanded care. This is generally an indication for elective intubation and mechanical ventilation, and these patients require admission to the ICU.
  • Parenteral corticosteroids are indicated, as is continued aggressive use of an inhaled beta2-adrenergic bronchodilator.
  • These patients may benefit from theophylline.
• Stage 4
  • This is a very serious stage in which the PO₂ is low and the PCO₂ is high, signifying respiratory failure.
  • These patients have less than 20% lung function or FEV₁ and require intubation and mechanical ventilation.
  • Patients in stage 4 should be admitted to the ICU. Switching from inhaled beta-2 agonists and anticholinergics to metered-dose inhalers (MDIs) via mechanical ventilator tubing is indicated.
  • Parenteral steroids are essential, and theophylline may be added, as with patients in stage 3.

• Search for CME/CE on This Topic »

• Status Asthmaticus (Pediatrics: Cardiac Disease and Critical Care Medicine)
• Asthma (Pediatrics: General Medicine)
• Asthma (Pulmonology)
• Rhabdomyolysis (Emergency Medicine)

• Asthma Center
• Asthma Causes
• Understanding Asthma Medications
• Asthma Overview
• Asthma Symptoms
• Asthma Treatment
• Asthma FAQs

• Experience With Use of Extracorporeal Life Support for Severe Refractory Status Asthmaticus in Children
• Levalbuterol for Severe Acute Asthma in Children?
• Measles-Mumps-Rubella Vaccination and Asthma-like Disease in Early Childhood