Asthma

Written By: Matt Tews
Medical College of Wisconsin, Milwaukee, Wisconsin

Edited By: Scott Sherman
John H. Stroger Hospital, Chicago, Illinois

Objectives

  • Recognize the clinical presentation of acute asthma
  • Understand the initial clinical approach to a patient with acute asthma
  • Demonstrate the use of appropriate diagnostic tests in an acute exacerbation
  • Initiate therapies based on clinical and objective information
  • Determine disposition depending on the severity of the exacerbation

Acute asthma is a common presentation to emergency departments (ED), accounting for more than 2 million visits per year in the United States. The presentation of acute asthma is typically referred to as an asthma "exacerbation." Patients present with a range of symptoms from coughing to difficulty breathing with audible wheezes to respiratory failure (rarely). Numerous medical conditions can present in a similar fashion, including pulmonary embolism (PE), pneumonia, congestive heart failure (CHF) acute myocardial infarction (AMI) or chronic obstructive pulmonary disease (COPD). However, acute asthma can often be differentiated with a simple history and physical exam.

Classic Presentation

Acute asthma is the result of an increase in inflammation of the airways as well as bronchospasm of the bronchial smooth muscles. An acute asthma presentation is characterized by progressive symptoms of shortness of breath, a non-productive cough, wheezing in all lung fields, and chest tightness due to a decrease in expiratory airflow. Patients typically present with symptoms that occur progressively over hours, days or weeks. The most common trigger of acute asthma is an upper respiratory tract infection. Those who present with sudden worsening of their symptoms are more frequently triggered by respiratory allergens, exercise, and psychosocial stress.

Adults with a history of asthma will often recognize their asthma symptoms and seek medical care when they cannot control the exacerbation at home with their usual medications. A history from a patient that they are experiencing their typical asthma exacerbation symptoms will often be all that is needed to guide further diagnosis and management. On the other hand, patients with asthma symptoms without a history of asthma, should have other diagnoses considered.

In the pediatric population, parents may bring their children into the ED with the chief complaint of coughing, decreased activity tolerance, or audible wheezing.

Initial Actions and Primary Survey

The first clinical decision that needs to be made when approaching a patient with an asthma exacerbation is whether there is an immediate need for definitive airway management. This would include rapid sequence induction and intubation for patients in severe respiratory distress AND one of the following:

  1. β2-adrenergic agonists (albuterol) or other medical therapies do not reverse symptoms
  2. Significant hypoxia even with supplemental oxygen
  3. Too tired to continue breathing on their own

Unlike other conditions which present with difficulty breathing, acute asthma requires definitive airway management in less than 1% of patients.

If the decision is made that the patient does not require immediate intubation, then the physician should begin a focused history and physical examination concurrently with the initiation of treatment (see below).

Initial historical questioning should include a history of previous episodes, prior ED visits, hospitalizations or ICU admissions, steroid use and a need for prior intubations. Insight should be gained into the overall asthma control, including how often inhalers are used, and compliance with the patient's medications.

Physical examination should start with the patient's general appearance, including color and accessory muscle use. Vital signs should be noted. Acute asthma patients are often tachycardic (between 90-120 beats per minute) and tachypneic. Auscultation of the lungs will help determine the amount of airflow present. An examination of the heart, pulses, extremities, lungs and neck (ie, jugular venous distention and stridor) is important to exclude other entities.

Initial Treatment

Oxygen, regardless of the severity of breathing, is required. It is usually administered in conjunction with an aerosolized β2-adrenergic bronchodilator through a handheld or facemask nebulizer device (see figure, left). Frequently the patient will already be started on a nebulizer treatment by the nurse or the paramedics by the time you see the patient. If this has not been done, the device is easy to put together and is connected to the green oxygen port and turned on with 6-8 L/min. Albuterol is a 0.5% solution that is mixed with 2 mL of saline and is placed in the nebulizer by unscrewing the top of the canister. Other methods of administering supplemental oxygen include a nasal cannula (mild exacerbations) or a non-rebreather mask (severe exacerbations)

The patient should be placed on a cardiac monitor and remain on continuous pulse oximetry. A room air pulse oximeter reading can be obtained if time allows, but should not significantly delay the administration of oxygen and albuterol. The goal of oxygen therapy should be to maintain SpO2 more than 92%. A peripheral intravenous (IV) line is indicated in moderate to severe exacerbations.

In a patient with a severe acute exacerbation that is not improving with aerosolized albuterol, subcutaneous epinephrine 0.2 mg or terbutaline 0.25 mg should be administered. Epinephrine is known to cause bronchodilation, but also has β1 and α-effects which can lead to side effects such as tachycardia or myocardial ischemia.

For patients who do not respond initially to albuterol, or who have a moderate to severe exacerbation, oral or intravenous corticosteroids should be administered early in the presentation. Onset of action is 4-6 hours.

Diagnostic Testing

The diagnosis of acute asthma in the ED is made by taking a thorough history and physical exam. The clinical presentation of asthma in a patient with a history of asthma is typically enough to diagnose and determine further management. For patients without a previous diagnosis of asthma and atypical symptoms, a more thorough evaluation may be needed to exclude other etiologies.

Diagnostic laboratory testing is not routinely indicated for an acute exacerbation in known asthmatics and should not delay initiation of treatment. However, if an underlying infectious source of the exacerbation is of concern, then a complete blood cell (CBC) count may be obtained, although its usefulness is limited as it may be elevated in acute asthma without an underlying infection. For patients who are taking theophylline for their asthma, a level may be drawn, but is not helpful in determining further management.

Arterial blood gas (ABG) determination is rarely necessary on acute presentation, and is only required when the patient remains hypoxic after the initiation of supplemental oxygen. Mild-to-moderate hypoxemia is a common arterial blood gas (ABG) finding. Hypocapnia and respiratory alkalosis may be present due to the increased respiratory rate of an acute asthma exacerbation, while prolonged or severe symptoms may results in hypercapnea and metabolic acidosis.

Chest radiography (CXR) is often normal, however findings can include hyperinflation of the lungs with flattened diaphragm if there is significant air trapping, supporting the diagnosis of asthma (click figure to enlarge). A CXR may be obtained if the cause of the patient's wheezing or difficulty breathing is uncertain. This is particularly helpful in patients with other comorbid conditions (i.e. CHF), fevers or concern for infection, an immunocompromised state or associated chest pain. Otherwise, it rarely changes management.

Electrocardiography (ECG) is not routinely helpful in the diagnosis of acute asthma. During an acute exacerbation, the ECG will often exhibit sinus tachycardia or potentially right ventricular strain. In patients who have associated chest pain or a history of CHF, an ECG may be helpful to evaluate for other potential causes of the patient's difficulty breathing or wheezing.

Pulmonary Function Tests (PFTs) performed at the bedside are the most useful objective test to aid in the treatment and disposition of a patient with an acute exacerbation of asthma. These tests confirm that the patient's symptoms are due to obstructive lung disease, assess the severity of the exacerbation, and monitor the response to treatment.

PFTs are measured by using a peak expiratory flow rate (PEFR) meter or a handheld spirometry machine that determines the forced expiratory volume in one second (FEV1) (see figures). Both devices measure the velocity of air flow and degree of airway obstruction. They are simple to use, but effort dependent. These values are obtained upon presentation to the emergency department and after each β2-adrenergic agonists treatment with the best predictor being the results at 1 hour after initiation of treatment.

Normal Predicted Peak Flows (Males)
Height
Age (years)60"65"70"75"80"
20554602649693740
25543590636679725
30532577622664710
35521565609651695
40509552596636680
45498540583622665
50486527569607649
55475515556593634
60463502542578618
65452490529564603
70440477515550587
Normal Predicted Peak Flows (Females)
Height
Age (Years)55"60"65"70"75"
20390423460496529
25385418454490523
30380413448483516
35375408442476509
40370402436470502
45365397430464495
50360391424457488
55355386418451482
60350380412445475
65345375406439468
70340369400432461
Normal Children & Adolescents
Height (inches)Males & Females
43"147
44"160
45"173
46"187
47"200
48"214
49"227
50"240
51"254
52"267
53"280
54"293
55"307
56"320
57"334
58"347
59"360
60"373
61"387
62"400
63"413
64"427
65"440
66"454

PEFRs obtained with a peak flow meter are interpreted using standard tables listing the normal values expected based on the sex, age and height of the patient. For example, a 35 year old man who is 5 foot 10 inches tall would have a predicted PEFR of 609. If that patient recorded a PEFR of 300, he is at approximately 50% of his predicted rate.

Peak flows can also be compared to the patient's reported baseline peak flow numbers, if known to them. If our 35 year old patient suffers with chronic asthma symptoms, and on a normal day his best peak flow is 350, then the 300 that he blew in the ED can be used relative to his normal "best" peak flow.

Treatment

The severity of the acute asthma presentation will determine the therapy. Exacerbations of asthma are classified based on objective measures of lung function using PEFR or FEV1. The severity of acute asthma and recommended treatments are shown in the figure (click to download). In general, asthma severity is divided up into mild exacerbations (> 70% predicted or personal best of PEFR), moderate exacerbations (40-69% predicted or personal best of PEFR) or severe exacerbations (<40% predicted or personal best of PEFR).

The goals of treatment include:

Individual treatment options are discussed as follows, but the core therapy around which acute asthma is managed involves β2-adrenergic agonists and the initial response to this therapy.

β2-Adrenergic Agonists

The first line therapy for acute asthma in the ED is inhaled β2-adrenergic agonists (available as albuterol) in all age groups. This medication can be given by two methods of delivery: metered dosed inhaler (MDI) or aerosolized solution (ie, nebulizer). Albuterol has an onset of action of 5 minutes and duration of action of 6 hours.

MDI are appropriate in mild to moderate exacerbations and is as effective as the aerosolized solution, giving a similar dose of medication in a shorter amount of time. To ensure more of the medication reaches the distal airways, and for maximum MDI effectiveness, a holding chamber (spacer) is used. The dose is albuterol two 90 mcg puffs into the spacer and then the patient inhales the aerosolized mist. This can be repeated every 4-6 hours. This method of delivery is used in the pediatric population with a mask on the end of the spacer that fits to the child's face.

Nebulized albuterol is usually administered every 20 minutes for up to 3 doses. Each dose is 0.5-1.0 mL (2.5-5 mg) of solution in 3 mL of saline. Higher doses of a continuous albuterol via a nebulizer is not necessarily more effective than repeated lower doses, but is frequently used in patients with severe exacerbations or when the patient does not respond to the initial 3 doses. The dose of "continuous" albuterol is 10-15 mg in 70 mL of isotonic saline. For children, the dose is 0.5 mg/kg/h.

Regardless of the route of delivery, the side effects of albuterol may include tremor, tachycardia and mild hypokalemia due to potassium being driven into muscle cells.

Anticholinergic agents

Ipratropium is an anticholinergic agent used in severe asthma or Beta-blocker induced asthma. There is evidence that combining it with a β2-adrenergic agonists may provide additional benefit compared to a β2-adrenergic agonists alone. Due to its anticholinergic effects, it may cause inhibition of airway secretions. It can be combined with albuterol in a nebulized treatment (Duoneb) or in MDI form (Combivent). It is not given as a single agent in acute asthma and has no further demonstrable benefit once a patient has been admitted to the hospital.

Corticosteroids

Corticosteroids are administered to reduce airway inflammation during exacerbations of acute asthma. Intravenous (IV) or oral (PO) formulation have an equal efficacy due to similar bioavailability. They are indicated in moderate to severe asthma exacerbations and in those who fail to respond to β2-adrenergic agonist therapy. High-risk patients who benefit from steroids are those with frequent ED visits for exacerbations, a history of intubation, currently taking steroids, or having a prolonged exacerbation. Onset of action is 4-6 hours, but it may take up to 24 hours to exert a significant clinical effect. The administration of corticosteroids in the acute setting has been shown to reduce the number of recurrent attacks after an exacerbation. Inhaled corticosteroids are a safe and effective treatment to prevent acute asthma. While they are not currently recommended in an acute asthma exacerbation, they should be prescribed at discharge in most patients.

Epinephrine

The Beta-agonist activity of epinephrine produces bronchodilatation. Epinephrine is reserved for patients who are seriously ill and not responding to serial treatments with inhaled β2-adrenergic agonists therapy. It is administered by the intramuscular (IM) or subcutaneous (SC) route. Evidence has shown that the IM route probably provides faster and more consistent delivery than the SC route. The adult dose is 0.3-0.5 mg IM q20min and the pediatric dose is 0.01 mg/kg up to 0.3-0.5 mg IM q20min, both given for up to 3 doses.

Magnesium sulfate

The use of IV magnesium sulfate has been shown to be beneficial in severe acute asthma, but the literature does not support routine use, especially in mild to moderate exacerbations. The usual dose in severe exacerbations is 2 gm IV over 20 minutes.

Antibiotics

Antibiotics should be reserved for patients with evidence of bacterial infection. There is no evidence that routine antibiotic dosing in acute asthma is beneficial.

Theophylline

The use of theophylline is not recommended in acute asthma. The combination use of IV aminophylline with β2-adrenergic agonists does not provide any additional clinical benefit. Side effects include tremors, nausea, anxiety, and tachyarrhythmia. In the unusual event that a patient is already receiving theophylline, a serum level should be measured.

Heliox

Heliox is a helium-oxygen (80:20 or 70:30) mixture that may provide benefit for ED patients with severe exacerbations. Helium has a lower density compared to room air, which allows it to travel through narrow air passages in a more laminar fashion instead of causing turbulence. This allows increased delivery of oxygen or bronchodilator medications to the alveoli, thereby decreasing the work of breathing. If a patient needs additional supplemental oxygen (thereby increasing the density of gas), the benefits of using heliox decrease and another method to deliver oxygen should be considered. The use of heliox is not routinely recommended as part of the initial therapy for an acute asthma exacerbation.

Non-invasive positive pressure ventilation

Non-invasive positive pressure ventilation (NPPV) provides inspiratory assistance as well as PEEP. It enhances patient breathing in acute respiratory conditions by providing rest in patients with significant work of breathing and early fatigue. While its use in COPD and CHF patients has been well established, the use of NPPV in acute asthma has been studied and is promising, but needs further evidence to determine the optimal recommendations.

Intubation

Intubation with mechanical ventilation may be required for severe acute asthma due to the increased work of breathing causing fatigue, persistent hypoxia or altered mentation. The goal is to maintain adequate oxygenation until the patient responds to therapies and mechanical ventilation can be withdrawn. However, intubation poses some significant management challenges. During mechanical ventilation, patients can develop high lung pressures because they are unable to expire a full breathe. This may result in barotrauma, pneumothorax or hypotension from decreased venous return. However, if all other therapies fail, intubation is necessary.

Disposition

The decision to discharge or admit a patient from the emergency department is not determined by the severity of their initial clinical presentation, but by their response to treatment over time measured by their PEFR or FEV1. The goal for discharge from the emergency department is to obtain more than 70 percent predicted or personal best FEV1 or PEFR.

Patients who meet this requirement and are clinically improved (lack of significant wheezing or accessory muscle use) with resolution of hypoxia can be discharged. Patients discharged should go home with a written asthma action plan, including how to deal with subsequent exacerbations, instructions on the appropriate use of medications and removal of any precipitating factors from their environment.

Patients who require multiple nebulizers in the ED or who have a moderate to severe exacerbation that demonstrates a good response to treatment in the ED, should be discharged home with a β2-adrenergic agonists and corticosteroids. Steroids can be given in the form of a short burst of medication for 4-7 days or a tapered dose over 10-14 days.

In patients who have an incomplete response to therapy (40-69% predicted), continued treatment in the ED may be necessary until symptoms improve, but these patients may also be considered for discharge depending on the clinical situation, including adequate follow-up and reliable compliance.

Patients with poor response to treatment, persistent severe symptoms, persistent hypoxia (< 90% SpO2) despite supplemental oxygen and those with a PEFR or FEV1 <40 percent predicted require additional therapies and should be admitted to the hospital, typically the ICU. Often these patients need time for the medications to take effect while undergoing close monitoring for the need for mechanical ventilation. Any FEV1 or PEFR <25 percent of predicted that improves by <10 percent after treatment indicates the need for an ICU admission.

Pearls and Pitfalls

Selected References