Airway pressure release ventilation in acute severe asthma: a case series and physiologic framework.

BACKGROUND: Acute severe asthma causes airflow obstruction, dynamic hyperinflation, and progressive hypercapnic respiratory failure. Conventional ventilation prioritizes prolonged expiratory times and permissive hypercapnia to limit air trapping, but some patients develop refractory hypercapnia requiring consideration of extracorporeal support. Airway pressure release ventilation (APRV) is traditionally used in hypoxemic respiratory failure, and its role in obstructive lung disease remains poorly defined. METHODS: We conducted a retrospective case series of adult patients with acute severe asthma who required invasive mechanical ventilation and underwent extracorporeal membrane oxygenation (ECMO) consultation at a tertiary academic center. Clinical characteristics, ventilatory parameters, arterial blood gases, and outcomes were collected. The primary outcome was change in PaCO2 and pH following APRV initiation. Secondary outcomes included the need for ECMO, duration of mechanical ventilation, and clinical outcomes. RESULTS: Six patients with marked hypercapnic respiratory failure (pre-APRV PaCO2 62-136 mm Hg; pH 6.68-7.20) were included. Five received APRV as a rescue strategy; one received APRV as a lung-protective adjunct concurrent with ECMO. Among the five rescue cases, PaCO2 decreased to 39-48 mm Hg and pH improved to 7.30-7.41. Time to physiologic improvement (PaCO2 ≤ 60 mm Hg and pH ≥ 7.30) ranged from 4 to 48 h. Four of five rescue patients were extubated within 48 h. No new barotrauma or major ventilator-associated complications occurred after APRV initiation. CONCLUSION: Following transition to APRV, hypercapnia and acidemia improved and none of the five rescue patients proceeded to ECMO cannulation. Whether this reflects APRV, concurrent medical therapy, or the natural course of treated bronchospasm cannot be determined from this small uncontrolled series. These observations suggest a flow-guided airway pressure release ventilation-time-controlled adaptive ventilation (APRV-TCAV) protocol was feasible and was applied without new barotrauma in refractory obstructive respiratory failure. Prospective controlled evaluation is needed to define APRV's role and identify patient phenotypes most likely to benefit.