Asthma

Objectives

Upon finishing this module, the student will be able to:

Recognize the clinical presentation of a child with acute asthma
Understand the initial management of a child presenting with acute asthma
Demonstrate the utility of diagnostic testing in an acute exacerbation
Initiate appropriate treatment for a pediatric acute asthma exacerbation

Introduction

Asthma is a chronic disease of the lungs that involves bronchial inflammation and hyperresponsiveness with intermittent reversible bronchospasm. Childhood asthma is a leading cause of emergency department visits and hospitalizations in the United States. Children who present with an acute asthma exacerbation or “attack” present with a variety of signs and symptoms. These include: cough, shortness of breath, wheezing, retractions, drowsiness, and respiratory failure with hypoxia and/or hypercarbia. Hypoxia is the inability to achieve adequate oxygenation due to severe bronchospasm, while hypercarbia is often a late-sign and is due to the inability to exhale carbon dioxide.

The differential diagnosis of children presenting with the above signs and symptoms include pneumonia, croup, bronchiolitis, pediatric congestive heart failure, pneumothorax, foreign body, and severe allergic reactions. The diagnosis of asthma can often be made with a thorough history and physical exam alone.

Primary Survey

When a child presents to the emergency department, they are often brought in for wheezing, persistent cough, decrease in level of activity, and/or an increased work of breathing.

The primary survey involves the following:

Is the child maintaining their airway? This can be assessed by their ability to speak or cry.
What is the oxygen saturation? Place child on pulse oximetry. If SpO2<94% then place on O2 to keep O2 saturations above 94%.
What is the general appearance of the child? Are they awake or drowsy? Can they speak in full sentences without pauses? Are they using accessory respiratory muscles, breathing fast, exhibiting retractions, nasal flaring, grunting, abdominal breathing, or cyanosis?
Auscultate the child’s lungs. Is there adequate air entry? Do you hear diffuse wheezing? Do you hear any focal areas of decreased breath sounds? Do you hear any rales or rhonchi?

Initial Actions

During the initial survey, if the patient is hypoxic, cyanotic, unresponsive, not maintaining an adequate airway, or showing signs of impending respiratory failure (“tiring out”), place the patient on oxygen while preparing for Rapid Sequence Intubation.
If there is any change in mental status, remember to check a bedside fingerstick glucose level and treat hypoglycemia if possible.
If the child does not need immediate intubation, complete primary assessment followed by complete physical exam, with focus on the ear, nose and throat to evaluate for other causes of symptoms.
If wheezing is present, begin a nebulized treatment with a short acting beta-agonist such as albuterol combined with a nebulized anticholinergic agent such as ipratropium. This will be discussed further in the treatment section below.

Presentation

Children with acute asthma exacerbations often present with shortness of breath, audible wheezing, cough (nocturnal), and increased work of breathing. Symptoms are usually gradual and progressive over several days with upper respiratory tract infection being a common trigger for bronchospasm. The history and physical exam alone is sufficient to diagnose an asthma exacerbation. It is also helpful to rule out other causes listed on the differential diagnoses above. The key findings are a previous history of asthma and wheezing on exam.

Patients in extremis may present limp or in altered mental status with no wheezing or air movement on exam.

Diagnostic Testing

The diagnosis and severity of an asthma exacerbation can be determined from a thorough history and physical exam alone. The severity can be assessed by the clinical presentation, vital signs, and peak expiratory flow rates (PEFR) in children who are old enough to perform this test, usually >8 years old. There is no indication for diagnostic laboratory tests or imaging in children with a known of asthma with clinical presentation consistent with asthma. A few ancillary tests with some utility in specific circumstances are listed below. However, prompt recognition and treatment of asthma should be initiated before any tests are ordered.

Laboratory tests: In known asthmatics, there is no indication for any laboratory testing. Some argue that if a fever is present with purulent productive sputum, and an infectious process in suspected, a CBC may be ordered. However, an elevated WBC count is non-specific and may be elevated from the acute asthma exacerbation itself.

Arterial Blood Gas (ABG): an ABG can be useful to help gauge the severity of an asthma exacerbation in moderate to severe exacerbations. Initial findings can be hypoxia and hypocarbia due to hyperventilation. However, as the symptoms progress and air-trapping gets worse, an ABG may show respiratory acidosis with hypercarbia. A venous blood gas (VBG) can be used as an alternative to an ABG in patients who are not hypoxic. Intubation should be based on clinical presentation and response to treatment alone and not based on blood gas values. However, repeating a VBG in patients with hypercarbia can assess the degree of improvement after treatment. If a trial of non-invasive positive pressure ventilation is conducted, a blood gas can also help assess response. An alternative to measuring blood gases would be using end-tidal carbon dioxide monitoring.

Chest X-Ray (CXR): A CXR should not be routinely ordered in children with an acute asthma exacerbation. A CXR should be considered in patients with rhonchi, uneven breath sounds, or areas of focal consolidation on lung exam, patients in respiratory failure, and patients not responding to treatment. Treatment should be initiated without delay if a diagnosis of asthma is made on initial evaluation. However, if there is suspicion of another process such as pneumonia, pneumothorax, or congenital congestive heart failure, then a CXR should be ordered.

Peak Expiratory Flow Rate (PEFR): PEFR can be used to assess asthma severity and response to treatment in children>8 years of age. Children are instructed to take a deep breath and blow as hard and as fast into the peak flow meter. Below are the normal values based on height (http://www.peakflow.com/paediatric_normal_values.pdf).

Treatment

The goals of treatment of an asthma exacerbation in the acute care setting are to reverse hypoxia, bronchospasm, and inflammation, while also aiming to prevent recurrence of another exacerbation. Below is a list of treatment options available:

Primary Agents

The mainstay of treatment in an acute asthma exacerbation is nebulized albuterol and ipratroprium bromide as well as corticosteroids, which can be given intravenously, intramuscularly, or orally.

Ipratroprium Bromide

Ipratropium Bromide is an inhaled anticholinergic agent which blocks cholinergic receptors, producing bronchodilation. It works synergistically with albuterol when nebulized together. It is also a mainstay therapy in an acute asthma exacerbation.
The nebulized dose is 0.25-0.5mg every 20min with a maximum of 3 doses.

Short Acting Beta Agonists

Albuterol is an inhaled short acting β2-adrenergic agonist. It is a critical component of treatment in an asthma exacerbation. It works by reversing bronchoconstriction.
It can be given as a nebulized treatment via a nebulizer or through an MDI with spacer. Studies have shown that there is no difference in effect or outcome between the two methods. Young children may not be able to use an MDI effectively. Therefore, nebulized albuterol is preferred in those children in the emergency department setting.
Inhaled albuterol has been found to be superior to oral, intravenous, and subcutaneous albuterol.
Albuterol can be given as stacked nebulized treatments of 0.15 mg/kg (minimum 2.5 mg) every 20 min for a maximum of 3 doses, the 0.15-0.3 mg/kg every 1-4 hours as needed. In severe exacerbation, continues nebulized albuterol has been shown to reduce hospitalization rates. The dose is 0.5mg/kg/hr, not to exceed 15mg/hr.
The side effects of albuterol are tachycardia, tremors, and hypokalemia. An alternative to albuterol is its racemic epimer levalbuterol.

Corticosteroids

Giving patients with an acute asthma exacerbation a corticosteroid is an integral part of treatment.
Acutely, corticosteroids can be given orally, intramuscularly, or intravenously. There is no evidence that one works better than the other. If the patient can tolerate oral therapy, it is preferred.
Inhaled corticosteroids are used primarily in maintenance therapy.
They work by reducing airway inflammation and by upregulating the production of beta receptors.
Early administration of steroids has been shown to reduce admission rates.
Prednisone, methylprednisolone, prednisolone, and dexamethasone are all steroids which are equally efficacious.
Prednisone, methylprednisilone, and prednisilone are given at a dose of 1-2mg/kg with a maximum dose of 60mg/day divided once to twice a day dosing for 5 days.
Dexamethasone is given at a dose of 0.6mg/kg with a maximum dose of 16mg for 2 doses over 2 days.

Adjunctive Agents

These agents are used in concert with the primary agents for patients with severe exacerbation or for those who are not responding to the primary agents alone.

Magnesium Sulfate

Promotes bronchodilation by relaxing bronchial smooth muscles.
Dosing is 25-75mg/kg up to 2g total IV over 20 minutes

Epinephrine (1:1000)

Promotes bronchodilation
Dosing is 0.01 mg/kg up to 0.3-0.5mg total SQ every 20min, up to a maximum of 3 doses

Heliox

Is a combination of 70% helium and 30% oxygen used to deliver albuterol.
It is less dense than oxygen and can provide more laminar flow through tight airways to delivery albuterol distally to obstructed bronchioles.
Not routinely recommended, but can be considered as adjunctive therapy in severe exacerbations.

Non-Invasive Positive Pressure Ventilation (NIPPV)

NIPPV has demonstrated efficacy in severe asthma exacerbation in the pediatric population with reduction of heart rate, respiratory rate, and decreased need for intubation.

Ketamine

Ketamine is a dissociative anesthetic used for induction in rapid sequence intubation and also can maintain sedation.
It has bronchodilative properties and is not routinely indicated but should be considered as an adjunctive agent in children with severe exacerbations requiring intubation.
Dosing is 0.3mg/kg IV bolus (maximum is 25mg), then 0.5mg/kg/hr for up to 2 hours

Intubation and Mechanical Ventilation

Intubation is indicated in children with persistent hypoxia, unresponsive hypercapnia with change in mental status, and respiratory fatigue due to increased work of breathing.
The decision to intubate is a clinical one and should not be delayed for any diagnostic testing or therapies when indicated.
If intubated, mechanical ventilation setting must allow adequate time for expiration due to air trapping from bronchospasm. The inspiratory to expiratory ratio should be adjusted to 1:4 to allow more time for expiration for each breath given by the ventilator. This prevents a phenomenon known as autoPEEP where air is trapped in the lung creating a persistently positive intrathroacic pressure leading to barotrauma and decreased venous return and hemodynamic collapse.

Pearls and Pitfalls

Asthma is a clinical diagnosis and routine imaging or testing is not required to make diagnosis and should not delay therapy.
Patients without wheezing may have more severe asthma than those with wheezing as these patients may have near-complete airway obstruction.
Early and aggressive treatment with steroids and inhaled albuterol is the mainstay of treatment. Delaying treatment can lead to increased morbidity.
Intubation is indicated in patients with impending respiratory failure not responsive to treatment. Signs of respiratory failure are persistent hypoxia, respiratory fatigue from increased work of breathing, and altered mental status.
A trial of NIPVV should be attempted in severe asthma exacerbations if possible.

References

Morris, Michael J. and Mosenifa, Mab. Asthma. MedScape. Sept. 2014. http://emedicine.medscape.com/article/296301-overview.
Wood, Pamela Runge and Hill, Vanessa L. Practical Management of Asthma. Pediatr Rev. 2009 Oct;30(10):375–85; PMID: 19797480
Dexheimer JW, Abramo TJ, Arnold DH, Johnson KB, Shyr Y, Ye F, Fan KH, Patel N, Aronsky D., Anasthma management system in a pediatric emergency department. Int J Med Inform. 2013 Apr;82(4):230–8. PMID:23218449
Schauer SG DO, Cuenca PJ Md, Johnson JJ Md, Ramirez S DO. Management Of Acute Asthma In The Emergency Department. Emerg Med Pract. 2013 Jun;15(6):1–28. PMID: 24040898