FORT LAUDERDALE, FLA. – When it’s necessary to mechanically ventilate a child with acute asthma, first stabilize the patient and then set the ventilator optimally to avoid major complications, Dr. Veda L. Ackerman said.

Intubation and initial ventilator set-up are the most critical times and require a high level of clinical skill, Dr. Ackerman said at a symposium on pediatric pulmonology sponsored by the American College of Chest Physicians and the American Academy of Pediatrics.

Supplemental oxygen to maintain saturation above 92% and an inhaled, short-acting beta-2 agonist such as albuterol also are important to lessen an acute asthma exacerbation, Dr. Ackerman said. Administer systemic steroids for all moderate to severe episodes that do not respond completely to beta-2 agonists, she said. Also consider adding the anticholinergic ipratropium bromide to combat any moderate to severe asthma attack.

This is standard of care in most emergency departments, but some children need more, Dr. Ackerman said.

The next step is intubation. "I had not seen a child with asthma intubated for years until the economy sank a few years ago. Then I saw three or four kids who died because they had not been taking their meds" and had acute episodes, said Dr. Ackerman, a pediatric intensivist at Riley Hospital for Children, Indianapolis.

Your decision to intubate or not to intubate relies on your clinical judgment, not on any specific pH or partial pressure of carbon dioxide (PaCO₂), Dr. Ackerman said. Keep in mind that generally fewer than 10% of children admitted to a pediatric ICU for severe asthma require intubation. Absolute indications include cardiopulmonary arrest, obtundation, profound hypoxemia unresponsive to therapy, and mixed respiratory and metabolic acidosis.

Once you decide to intubate, there is only a minimal margin of error if the child is hypoxic, acidotic, and fatigued, Dr. Ackerman said. An effective rapid sequence intubation relies on preoxygenation with 100% oxygen using a facemask during spontaneous breathing and a combination of ketamine and a benzodiazepine for sedation and analgesia. "Avoid assisted breathing with an Ambu bag until the tube is placed, or you will have emesis or worsening of your air trapping." Also consider use of a cuffed endotracheal tube because some children require high ventilatory pressures in the ICU.

In the "next critical 5 minutes" after intubation, a natural tendency for many clinicians may be to hyperventilate the patient using a self-inflating bag valve mask resuscitator such as an Ambu bag. This is ill advised, Dr. Ackerman said. "In the asthmatic child, this will impede exhalation, leading to worsening hypercapnia and acidosis with potential cardiac collapse, as well as increased risk of barotrauma due to worsening hyperinflation," she said.

"Eventually, the best thing is to put them on a ventilator," Dr. Ackerman said. Reversal of hypoxemia, relief of respiratory muscle fatigue, and allowing enough time for inflammation and bronchospasm to respond to systemic steroids and bronchodilator therapy are among the goals of ventilation. "These kids are exhausted and need to rest."

Initial ventilator settings are based on physician choice. Most clinicians use volume control, although pressure control can be used instead to leak peak pressure, Dr. Ackerman said. Assist control or pressure-regulated volume control are other ventilator options. "There is no evidence to suggest one mode is superior, provided one understands the specific characteristics of each mode," she said.

"We start at 100% oxygen. There is no reason to worry about hyperoxygenation of a child with asthma," Dr. Ackerman said. Tidal volume is initially set between 8 and 12 mL/kg to achieve adequate chest movement with each ventilator breath and to keep peak pressures below 50. Set the rate below the physiologic breathing rate for the child to allow enough time for the exhalation phase, she advised. The inspiratory-expiratory ratio should be at least 1:4, but may need to go as high as 1:8. "You don’t want to stack the breaths," as barotrauma may result if a breath is not fully exhaled before the subsequent breath starts, she added.

Permissive hypercapnia is another strategy to minimize risk of barotrauma. "CO₂ is not going to hurt the child if the pH is at a normal level," Dr. Ackerman said. Limited duration, permissive hypercapnia is accomplished by reducing tidal volume to 7 mL/kg or less, keeping peak airway pressure a maximum of 40 cm H₂O, and allowing PaCO₂ to rise no more than 10 mm Hg per hour up to a maximum of 80-100 mm Hg. At the same time, maintain oxygen saturation above 90%, allow at least 4 seconds for expiration, and set low minute ventilation (10 L/min or less) and low respiratory rate (fewer than 10 breaths per minute) (Intensive Care Med. 2006;32:501-10).

In addition to barotrauma, monitor patients for any signs of ventilator-associated pneumonia, massive gastrointestinal bleeding, and hypotension and circulatory compromise from poor venous return, Dr. Ackerman said. "If there is an acute change, think pneumothorax unless proven otherwise."

Dr. Ackerman said that she had no relevant disclosures.

Pediatric Acute Asthma May Require Mechanical Ventilation