Pediatric Status Asthmaticus Follow-up

• Indications for ICU admission

  • Altered sensorium
  • Use of continuous inhaled beta-agonist therapy
  • Exhaustion
  • Markedly decreased air entry
  • Rising PCO₂ despite treatment
  • Presence of high-risk factors
  • Failure to improve despite adequate therapy
• Indications for intubation and mechanical ventilation

  • Apnea or respiratory arrest
  • Diminishing level of consciousness
  • Impending respiratory failure marked by significantly rising PCO₂ with fatigue, decreased air movement, and altered level of consciousness
  • Significant hypoxemia that is poorly responsive or unresponsive to supplemental oxygen therapy alone
• Considerations in mechanical ventilation

  • The decision to intubate a patient with asthma is taken with extreme caution. Positive pressure ventilation in a patient with asthma is complicated by severe airway obstruction and air trapping, which results in hyperinflated lungs that may resist further inflation and places the patient at high risk of barotrauma. Therefore, mechanical ventilation should be undertaken only in the face of continued deterioration despite maximal bronchodilatory therapy.
    • Asthma is a disease of airway obstruction (ie, increased airway resistance), resulting in prolongation of the time constant (the time needed for lung units to fill and empty). Slow ventilator rates are usually needed.
    • In the face of high peak airway pressures, the principle of mechanical ventilation of status asthmaticus is controlled hypoventilation, tolerating higher levels of PCO₂ in order to minimize tidal volume and peak inspiratory pressures. Permissive hypercapnia can be tolerated as long as the patient remains adequately oxygenated. A longer I:E ratio, often greater than 1:3-4, helps allow time for optimal exhalation, facilitating ventilation and avoiding excessive further air-trapping (auto-PEEP).
  • The use of positive end-expiratory pressure (PEEP) is controversial. A patient with status asthmaticus in respiratory failure on mechanical ventilation usually has a significant amount of air trapping that results in intrinsic PEEP, which may be worsened by maintaining PEEP during exhalation. However, some patients may benefit by the addition of PEEP, perhaps by maintaining airway patency during exhalation. Thus, in a patient who remains refractory to the initial ventilatory settings with no or very low PEEP, cautiously increasing the PEEP may prove beneficial.
  • Traditionally, slow controlled ventilation with heavy sedation, often with muscle relaxation, is used to ventilate patients with status asthmaticus. Caution is warranted, however, as use of muscle relaxants together with high-dose steroids has been associated with the development of prolonged paralysis.
  • Alternatively, some practitioners report ventilating children with status asthmaticus with pressure support alone. This strategy may allow the patient to set his or her own respiratory rate as determined by the physiologic time constant, while assisting ventilation and relieving the fatigue due to significantly increased work of breathing.
  • Noninvasive positive pressure ventilation (NPPV), such as continuous positive airway pressure (CPAP) or bimodal positive airway pressure (BiPAP) delivered through a face mask, has been used for support of status asthmaticus. NPPV has been shown to "splint" the airways, allowing for better exhalation and emptying.
  • Patients require supportive measures and monitoring during mechanical ventilation.
    • Patients may be uncomfortable and air hungry while ventilated with low respiratory rates, prolonged exhalation times, and hypercapnia due to a strategy of controlled hypoventilation.
    • Ideally, monitor flow-volume loops to ascertain if adequate time is provided for exhalation to avoid breath stacking, which occurs if the next breath is delivered before exhalation is completed. Monitoring exhaled tidal volume and auto–positive end-expiratory pressure (auto-PEEP) is also important.
    • Fluids and electrolytes should be monitored. Before arrival in the hospital, children with status asthmaticus have often had diminished oral intake and may have been vomiting because of respiratory difficulty or adverse effects from their medications. This leads to decreased intravascular volume status that may be potentiated by the effects of positive pressure ventilation.
    • In addition, cardiac output may be decreased because of decreased preload that results from air trapping and auto-PEEP. This decreased cardiac output and intravascular volume may be accompanied by metabolic acidosis. Intravascular fluid expansion is needed to treat hypoperfusion, hypotension, or metabolic acidosis. In addition, diastolic hypotension may occasionally result from high doses of beta-agonists. A vasoconstrictor (ie, norepinephrine, phenylephrine) may be considered if significant diastolic hypotension in the face of adequate intravascular volume persists. Monitor serum electrolyte levels, as medications used to treat asthma can result in significant kaliuresis.
• Indwelling arterial catheters: Placement of indwelling arterial catheters provides continuous blood pressure monitoring, as well as arterial blood gas sampling, in mechanically ventilated patients. Blood gases should be monitored to assess response to mechanical ventilation support.

• Outpatient follow-up and continued care of a patient who is hospitalized in the pediatric ICU because of severe status asthmaticus is important in optimizing long-term outcome and quality of life and minimizing recurrent episodes of severe asthma exacerbation.
• Follow-up is best provided by a specialist in the treatment of asthma.
• Among the important considerations are home medications, such as anti-inflammatory agents. Corticosteroids are now considered the mainstays of asthma maintenance therapy. Studies indicate that the underuse of anti-inflammatory agents is related to more severe asthma. This is thought to be due to airway remodeling and the persistence of inflammatory changes.
• Bronchodilators are recommended for acute exacerbations.
• Environmental management is also necessary in those children with environmental allergies.

• Medications include bronchodilators for inhalation such as albuterol, inhaled steroids, oral agents such as leukotriene antagonists, and/or theophylline.
• Corticosteroid therapy, if indicated, should include written instructions on corticosteroid use.

A child admitted to the ICU with severe status asthmaticus may be considered for transfer to an inpatient ward once the patient meets the following criteria:

• The child has been successfully extubated.
• The child has been weaned off continuous intravenous beta-agonists (ie, terbutaline, aminophylline, if used) and is stable on intermittent beta-agonist aerosol therapy.
• The child can tolerate cessation of continuous albuterol and is converted to intermittent albuterol nebulization at a frequency that can be delivered on the general pediatric floor.
• The child has a stable hemodynamic status.

• The goal of chronic asthma therapy is the prevention of admission. This article, however, addresses severe acute exacerbation of asthma (status asthmaticus).

Complications may include the following:

• Cardiac arrest
• Respiratory failure or arrest
• Hypoxemia with hypoxic ischemic CNS injury
• Pneumothorax or pneumomediastinum
• Toxicity from medications

• Asthma is a chronic illness. Patients and their families must be provided with a team that can offer education and follow-up care. Prior to discharge, the team that provides asthma education should meet with the family and the patient to impart information regarding maintenance and monitoring and environmental control.
• For patient education resources, see the Asthma Center, as well as Asthma, Asthma FAQs, Understanding Asthma Medications, and Asthma in School Children: Educational Slides.