Respiratory mechanics in status asthmaticus. Effects of inhalational anesthesia

The incidence and severity of bronchial asthma has increased considerably in recent years. As a result, the number of patients requiring mechanical ventilation and more intensive medical therapy for treatment of refractory asthma has also increased. Despite this, available information concerning the quantitative changes in respiratory mechanics and the response to treatment that occur in such patients is limited. The present study describes the abnormalities in respiratory mechanics and the response to isoflurane anesthesia observed in three adults mechanically ventilated for treatment of status asthmaticus. Airway pressure, flow, and volume were measured during controlled mechanical ventilation in which the airway was periodically occluded in order to determine respiratory system mechanics. In two patients, the volume of hyperinflation and expiratory volume-flow relationship were also obtained. Inspiratory and expiratory indices of respiratory resistance were markedly abnormal. These abnormalities were associated with significant dynamic hyperinflation and high levels of intrinsic PEEP. Expiratory flow limitation was also identified in two patients by failure of low levels of applied positive end-expiratory pressure (PEEP) to alter the expiratory volume-flow relationship. Indices of respiratory resistance as well as the magnitude of dynamic hyperinflation and intrinsic PEEP improved considerably with isoflurane administration, after having been refractory to intensive conventional bronchodilator therapy. In summary, these results demonstrate the severity of abnormalities in respiratory mechanics present in ventilated patients with status asthmaticus and the potential therapeutic efficacy of inhalational anesthesia in this setting.