Donald H. Arnold
Eighty percent of wheezing in patients <1 year is due to viral bronchiolitis and resolves by 3 years.
Wheezing implies diffuse or focal obstructive lower airway disease.
Dynamic airway compression results in auto-PEEP with increased work of breathing and V/Q mismatch.
V/Q mismatch results in mild hypoxemia (>92%) that responds to minimal oxygen supplementation. If more severe hypoxemia, consider pneumonia or pneumothorax.
Wheezing may diminish as air entry becomes more compromised.
Air entry and accessory muscle use are the most valid bedside measures of severity but may diminish if the patient becomes fatigued.
Retractions progress in a rostral-caudal direction with subcostal, intercostal, and supraclavicular accessory muscle use.
DIAGNOSIS AND DIFFERENTIAL
Asthma and bronchiolitis account for most episodes of wheezing, but other causes should always be considered (Table 72-1).
TABLE 72-1 Differential Diagnosis of Wheezing According to Presenting Signs and Symptoms
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Determine precipitating events and whether wheezing is diffuse or localized.
Quickly evaluate for adequacy of air entry, work of breathing, and oxygenation.
Use standardized respiratory distress score to establish baseline severity and response to treatment.
Fatigue, drowsiness, and altered mental status are signs of respiratory failure.
Asthma is the most common chronic disease of childhood and most frequent reason for pediatric hospitalizations in North America.
Exacerbations occur in 57% of children with asthma and account for 640,000 ED visits each year.
Rhinovirus wheezing illnesses in early childhood are the strongest predictor of asthma at 6 years of age. Other risk factors include second-hand smoke exposure, urban household (cockroach) exposure, family history, and race (non-Hispanic black children).
Near-fatal or fatal asthma may occur even in patients with previously mild episodes. Risk factors include massive allergen exposure, emotional distress, obesity, limited access to health care, improper medication administration, history of prior respiratory failure, African-American race, and impaired perception of dyspnea.
The primary pathophysiologic event is airway inflammation, leading to airway hyperresponsiveness and obstruction. Each of these three components must be treated.
The most common triggers are allergens, irritants, and viral respiratory infections.
Bronchospasm, mucosal edema, and mucous plugging cause variable and reversible airflow obstruction, dynamic airway compression, and V/Q mismatch. Airway obstruction may become nonreversible over time.
During early stages of exacerbation, mild hypoxemia and hypocapnia with respiratory alkalosis are observed. With decreasing alveolar ventilation, increased work of breathing and tissue hypoxia, Paco2increases and metabolic acidosis may predominate over respiratory alkalosis. Thus, rising Paco2 may be an ominous indicator of respiratory failure.
Acute asthma exacerbations comprise progressively worsening wheezing, cough, shortness of breath, and/or chest tightness. Any exacerbation may progress to unresponsive asthma (status asthmaticus), respiratory failure, and fatal asthma.
Wheezing, cough, dyspnea, and fever (due to viral illness as precipitant) are the most common manifestations of an acute asthma exacerbation.
The quiet chest is an ominous sign of severely compromised ventilation and indicates airflow insufficient to generate wheezing.
Critical elements of physical assessment include mental status, accessory muscle use, respiratory rate, and air entry by auscultation.
Hypoxia may result in agitation, whereas somnolence may result from hypercarbia and indicate respiratory failure and impending arrest.
End-tidal CO2 monitoring may be useful but may not be sensitive to rising Paco2 if alveolar emptying is impaired.
Pulsus paradoxus and PEF or FEV measurement are recommended by NHLBI guidelines but accurate measurement is difficult in the ED environment.
DIAGNOSIS AND DIFFERENTIAL
Essential diagnostic questions are (1) Does this patient have asthma? (2) What is the severity of airway obstruction? (3) Is there a treatable condition that precipitated the exacerbation?
Most children <3 years with wheezing do not have asthma. Children >3 years with wheezing, dyspnea, or cough that responds to albuterol may be given a provisional diagnosis of asthma. Spirometry for FEV is the criterion standard for airway obstruction but is generally not possible in children <6 years and in those in respiratory distress.
Indications for chest radiograph in asthma include a first episode of wheezing, localized findings (dullness or rales) that do not resolve with bronchodilator treatment (possible foreign body or pneumonia), significant chest pain (possible pneumothorax), or respiratory distress out of proportion to the degree of airflow limitation. Viral infections are the most common precipitant, and thus many patients present with fever. Presence of fever alone is not an indication for chest radiograph. Chest radiograph findings include hyperinflation and atelectasis.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Quickly identify the patient experiencing an acute severe exacerbation and escalate therapy as appropriate to prevent respiratory failure.
Oxygen should be administered if saturation is <95%. Titrated oxygen to maintain saturation 95% to 98% may result in more rapid resolution of V/Q mismatch.
Albuterol is the mainstay of treatment and can be administered by Metered Dose Inhaler (MDI) with expansion chamber (4–8 puffs every 20 minutes × 3 doses then Q 1–4 hours); by intermittent nebulization (0.15 milligram/kg, or 2.5 milligrams, every 20 minutes × 3 doses, then 0.15–15.0 milligram/kg up to 10 milligrams every 1–4 hours); or by continuous nebulization (0.5 milligram/kg/h).
Ipratropium should be administered with nebulized albuterol (0.25–25.0 milligram Q 20 minutes × 3 doses).
Systemic β-agonists have no advantage over inhaled albuterol except in the patient with minimal ventilation. Terbutaline can be administered SQ (0.01 milligram/kg, max 0.4 milligram, Q 20 minutes × 3 doses) or IV (0.01 milligram/kg load over 5–10 minutes then 0.001–001.0 milligram/kg/min). Epinephrine has β- and α-agonist activity that may shrink edematous mucosa (SQ: 0.01 milligram/kg, max 0.5 milligram, Q 15 minutes).
Systemic corticosteroids (CCS) should be considered in all but the mildest cases that respond immediately to albuterol. CCS decrease airway inflammation and increase the effectiveness of β2-agonists. Early administration decreases hospital admission rates. Prednisone (2 milligrams/kg/d, maximum 60 milligrams/d) as a 3 to 5 day course is usually sufficient and does not require tapering. Dexamethasone, 0.6 milligram/kg administered orally (IV formulation) or IM as a single dose may be as effective as a 3 to 5 day course and better tolerated (less vomiting). These medications are generally contraindicated in varicella-susceptible patients who have or might have exposure to varicella.
Magnesium sulfate (50–75 milligrams/kg, maximum 2 grams, IV over 10–20 minutes) may provide rapid bronchodilation in the patient who is not ventilating sufficiently for nebulized albuterol delivery to peripheral airways.
Ketamine (2 milligrams/kg IV followed by 2–3 milligrams/kg/h) is an effective bronchodilator and may delay or prevent respiratory failure and the need for assisted ventilation in the patient with severe status asthmaticus.
Helium-oxygen (Heliox) as a 60:40 or 70:30 (helium:oxygen) mix may restore laminar airflow and improve alveolar ventilation. Nebulized albuterol may be administered with this treatment.
IV fluids should be considered for the patient in status asthmaticus who has decreased oral intake or who is NPO due to the severity of the episode.
Aminophylline is no longer recommended by the NHLBI guidelines.
Respiratory failure may be avoided by rapid escalation of the above treatments. However, patient fatigue or persistent bronchospasm may nonetheless occur, and for this reason the need for endotracheal intubation and mechanical ventilation should be anticipated and planned. Laryngoscopy may precipitate severe laryngo- or bronchospasm; the decision to intubate should be carefully considered. Rapid-sequence intubation may include premedication with atropine (0.02 milligram/kg, minimum 0.5 milligram; maximum 1 milligram) and lidocaine (1.5 milligrams/kg) and sedation with ketamine (2 milligrams/kg), followed by paralysis using succinylcholine (2 milligrams/kg) or rocuronium (1 milligram/kg) to provide optimal intubating conditions.
Hospital admission is necessary for children who do not respond adequately to treatment (eg, persistent hypoxemia or failure to normalize aeration over 2–4 hours) or whose caretaker may not be able to provide necessary ongoing care.
Discharge planning should include an “action plan” (available at http://www.nhlbi.nih.gov/health/public/lung/asthma/actionplan_text.htm), albuterol as MDI or nebulizer, oral CCS, and follow-up with the primary care provider.
Inhaled corticosteroids should be prescribed for all patients with persistent asthma (as defined by NHLBI at Web site above).
Bronchiolitis affects 20% to 30% of all infants and is most frequent lower respiratory infection in first 2 years of life.
Respiratory syncytial virus (RSV) and rhinovirus are the most common viruses associated with this illness, with RSV predominating during winter and rhinovirus in fall and spring.
Peak bronchiolitis season is November to March but may occur throughout the year.
Infants less than 2 years old are most commonly affected. The peak incidence in urban populations is 2 months of age.
Young infants and those with history of prematurity, bronchopulmonary dysplasia, congenital heart disease, or immunosuppression are at increased risk of complicated courses of disease.
Infection is highly contagious and is transmitted by direct contact with secretions and self-inoculation by contaminated hands via the eyes and nose. Infection does not confer immunity, and infants may develop multiple episodes.
There is acute airway inflammation and edema, small airway epithelial cell necrosis and sloughing, increased mucus production and mucus plugging, and bronchospasm, all of which vary considerably between patients and over the course of the illness.
Nasal passages account for 50% total airway resistance and thus suctioning is usually beneficial. Increased overall airway resistance and decreased compliance result in increased work of breathing.
Sustained immunity does not reliably occur, and reinfection with recurrence of illness is common.
Clinical features indicate severity of illness and include dyspnea, coryza, cough, wheezing, variable hypoxemia, use of accessory muscles, nasal flaring, and poor feeding.
Severity increases over the first 3 to 5 days with a total duration of illness of 7 to 14 days.
Apnea (see below), cyanosis, or altered mental status or fatigue are ominous signs and may portend respiratory failure.
Somnolence or apparent fatigue (including an inability to take fluids) or significant hypoxia or cyanosis signify more severe illness and warrant greater intensity of observation or intervention.
Infants at risk of apnea include those who were born at <37 weeks gestation and are <12 weeks of age or postconception age <48 weeks; born at term but <4 weeks of age; have had witnessed apnea; have hemodynamically significant congenital heart disease (CHF, moderate to severe pulmonary hypertension, cyanotic lesions); have chronic lung disease (BPD, congenital malformations, CF); or are immunocompromised.
DIAGNOSIS AND DIFFERENTIAL
Diagnosis is clinical and should not routinely involve laboratory or radiologic studies. Routine chest radiograph is not indicated for mild and typical episodes without focal chest findings.
Patients with severe disease, possible respiratory failure, and/or apnea should be identified early.
Testing for RSV or other pathogens and other lab studies is not routinely indicated.
Serial assessment and oximetry is a key component for disposition decisions.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Nasal suctioning and saline drops: nasal airflow resistance is 50% of total airways resistance and suctioning of the nasal passages after saline instillation alone may substantially decrease work of breathing, correct hypoxemia, and enable the patient to feed normally. Nasal vasoconstrictors are not indicated and have resulted in tachydysrrythmia.
Oxygen saturation should be maintained >92%. Hypoxemia may result from V/Q mismatch and require minimal supplemental oxygen, or may result from significant airspace (alveolar) disease and require more intensive treatment.
Nebulized α- and β-agonists should not be routinely used. However, use of a β2-agonist (albuterol) might be considered, particularly if there is a personal or family history of asthma.
Epinephrine (0.5 mL of 1:1000 in 2.5 mL saline) may be beneficial due to α-agonist mediated mucosal vasoconstriction with reduction of edema. If these medications are used, an objective measure (eg, respiratory rate or bronchiolitis score) should be used to assess response.
Nebulized hypertonic saline (3% or 5%, 3–5 mL by nebulizer) may decrease mucus production and viscidity and, if beneficial, may be administered every 4 hours.
Hydration should be assessed and managed with IV fluids if necessary. Patients with bronchiolitis may not be able to feed normally, and respiratory rates >60/minute increase the risk of aspiration.
Helium-oxygen (heliox) may delay or prevent respiratory failure and need for intubation.
Noninvasive ventilation (CPAP or BiPAP) may improve oxygenation and ventilation, decrease work of breathing, and delay or obviate the need for endotracheal intubation. Additionally, application of CPAP may prevent further apnea in affected infants.
CCS should not be used routinely for patients with bronchiolitis. A single study suggests potential synergy when high-dose CCSs are coadministered with racemic epinephrine.
Disposition decision making must consider the timepoint of disease progression (severity increases over the first 3–5 days of illness), the ability of caretakers to manage the illness, the availability of follow up, and whether risk factors for apnea and/or severe disease are present.
Indications for hospitalization include persistent hypoxia, tachypnea, increased work of breathing, and inability to feed or maintain hydration. Discharged patients should have follow-up with their primary care provider within 24 hours.
For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 120, “Wheezing in Infants and Children,” by Donald H. Arnold, David M. Spiro, and Melissa L. Langhan.