Acute Severe Asthma (Status Asthmaticus)
Asthma is the most common condition requiring hospitalization in children, and it accounts for a large proportion of PICU admissions. Acute severe asthma (status asthmaticus) refers to patients who are unresponsive to traditional asthma therapies on presentation, including repeated doses of beta-agonists. This distinct patient population has severe asthma exacerbations and is at risk for acute respiratory failure from severe bronchospasm. Few studies exist to guide the evidence-based management of status asthmaticus in the pediatric population. Therefore, practice patterns vary based on local preference and experience. In this section, we review the management of acute severe asthma, including therapies for refractory bronchospasm.
The assessment of the patient in status asthmaticus is directed at identifying signs and symptoms of imminent respiratory arrest. Attention must be paid to the patient’s work of breathing, lung exam, and hemodynamic parameters.
Signs of increased work of breathing include:
- accessory muscle use
- head bobbing in very young children
Classic findings of asthma on lung examination include:
- poor aeration
- prolonged expiratory phase
However, severe bronchospasm often can present with a “quiet chest,” in which bronchoconstriction is so severe that wheezes are not heard. Attention to volume status is essential because many patients will be volume depleted due to insensible losses. Careful attention to fluid status is paramount to avoid complications of the vasodilatory effects of beta-adrenergic therapies while balancing the risk of pulmonary edema.
Several asthma-severity scores have been designed to guide the stepwise approach to the treatment of the patient with severe asthma and the weaning of medications. One example is the WARME Respiratory Score:
WARME Respiratory Score*
||Entire expiratory/any inspiratory
||One area decreased
||More than one area decreased
||Tachypneic for age
||Any neck or abdominal retractions
||Expiratory >3x inspiratory
The goals of the ICU management of the patient in status asthmaticus are threefold:
1. to reverse airway obstruction quickly with the aggressive use of beta-agonists and corticosteroids
2. to correct or prevent hypoxemia with supplemental oxygen therapy
3. to avoid or treat complications of airway obstruction and respiratory support, including air leak syndromes and respiratory arrest
- Beta-2-adrenergic agonists are the mainstay of alleviating life-threatening bronchoconstriction. Inhaled albuterol is the most commonly used medication and can be delivered continuously through a variety of options, including high-flow nasal cannula systems or face mask. Maximum doses vary by institution but typically range from 5 mg/hour to ≥40 mg/hour.
- Ipratropium bromide is an inhaled anticholinergic therapy that is frequently added to a patient’s medication regimen when requiring ICU admission (usually 25–50 µg inhaled every 6 hours). Studies have shown little to no benefit in hospitalized adult patients, and no studies have been conducted in PICU patients.
- Magnesium sulfate is another potent bronchodilator (dose range, 25–75 mg/kg IV; maximum dose, 2 g) over 20 to 30 minutes if not administered before ICU admission. Evidence of benefit from repetitive dosing is lacking.
Glucocorticoids are the medications of choice for treatment of acute severe asthma to decrease inflammation. They are typically given intravenously due to an inability to tolerate oral intake in infants and children with respiratory distress. Methylprednisolone is usually given in doses up to 4 mg/kg/day (maximum dose, 60–125 mg/day based on age and weight).
Medications for Refractory Severe Acute Asthma
Patients who do not respond rapidly to the therapies described above are likely in danger of respiratory arrest and the need for invasive mechanical ventilation. Treatment in such patients includes the addition of IV beta-agonists such as terbutaline, aminophylline or theophylline, and ketamine infusions. Inhaled anesthetics have also been used for those with super-refractory bronchoconstriction at available institutions.
Patients who continue to worsen despite maximal medical management may benefit from the use of noninvasive positive-pressure ventilation (NPPV). NPPV may decrease the work of breathing created by airflow obstruction and air trapping.
If, despite maximal medical management, respiratory arrest is imminent, intubation and mechanical ventilation can be employed. Intubation is reserved for the most refractory patients given the risk of severe, life-threatening bronchospasm that can occur with direct laryngoscopy. Additionally, mechanical ventilation in the asthmatic patient is quite challenging. Dynamic hyperinflation can occur with severe airflow obstruction, leading to initiation of the next ventilated breath prior to full exhalation and contributing to alveolar overdistention that can result in hypoxemia, hypotension, or alveolar rupture. Thus, experienced intensivists and respiratory therapists must be available to carefully minimize the risks of barotrauma and air leak syndromes.
Extracorporeal membrane oxygenation (ECMO) has also been used at some centers with ECMO capability for extreme cases in which optimal ventilation cannot be achieved.