Ventilating the patient with severe asthma: nonconventional therapy

Conventional pharmacotherapy of severe asthma and status asthmaticus includes beta2-sympathomimetics, theophylline, corticosteroids and occasionally topical anticholinergics (ipratropium bromide). Since hypoxemia is the most severe phenomenon in status asthmaticus the administration of oxygen is mandatory. However, if the bronchodilating therapy fails and hypoxemia continues, usually respiratory failure develops due to progressive respiratory muscle failure. An increasing PaCO(2) and respiratory acidosis are indications for mechanical ventilatory support to unload the failing respiratory pump. Nowadays, there is increasing consensus that ventilatory support should be administered primarily as non-invasive ventilation (NIV) via a face mask1. However, in a significant number of patients with severe asthma NIV is either contraindicated or insufficient. In this case usually the patient must be endotracheally intubated and mechanically ventilated "invasively". Intubation and ventilation of patients with severe asthma or status asthmaticus is associated with a high incidence of complications compared to patients ventilated for other causes of respiratory failure2,3. Therefore the risks of invasive mechanical ventilation have to be weighted carefully to ongoing conservative therapy and NIV. Cardiopulmonary arrest and severe hypoxemia in spite of O2 supplement and NIV are absolute criteria for intubation and ventilation. Mostly deterioration in mental status and exhaustion are the clinical findings leading to mechanical ventilation. Decision is guided rather by the course of the deterioration (how fast the patient's condition is worsening) than by pathological values alone. An increased PaCO(2) with moderate respiratory acidosis alone is not per se an indication for mechanical ventilation. However, a continuously rising PaCO(2) or the development of a severe metabolic acidosis after 1 hour of NIV is a strong argument for invasive mechanical ventilation. Other criteria are evidence of cardiac failure with fall in pulse volume and dysrhythmias, pneumomediastinum or pneumothorax (which has to be drained before mechanical ventilation!).