HELIOX THERAPY IN ACUTE SEVERE ASTHMA

Study objective: To assess how patients with respiratory acidosis from acute severe asthma respond to helium-oxygen (heliox) mixtures. Design: Consecutive case series. Setting: Urban community teaching hospital. Patients: Over a 2-year period, 12 asthmatics (mean age, 33.8 +/- 11.3 years) presented to the emergency department with acute respiratory acidosis (pH <7.35 and PaCO2 greater than or equal to 45 mm Hg). All 12 patients were treated with heliox (60 to 70% helium/30 to 40% oxygen). Five patients received heliox through a ventilator and seven received heliox via face mask. Results: Arterial blood gases (ABGs) were drawn immediately before and at a mean of 49.2 +/- 25.2 min after beginning heliox therapy. No therapeutic interventions were made between ABGs. For the entire group, the mean PaCO2 decreased from 57.9 to 47.5 mm Hg (p<0.005) and the arterial pH increased from 7.23 to 7.32 (p<0.001). In an attempt to find characteristics that might predict the response to heliox, a clinically significant response to heliox was defined as a drop in PaCO2 (to normal or by greater than or equal to 15%) coupled with a rise in pH by greater than or equal to 0.05. Using this definition, there were eight responders (67%) and four nonresponders (33%). The responders had a shorter duration of symptoms (17.8 vs 78.0 h, p<0.05) and a lower preheliox pH (7.20 vs 7.30, p<0.05). All of the responders presented within 24 h of symptom onset. Three of the four nonresponders reported prolonged (greater than or equal to 96 h) duration of symptoms, and two eventually required intubation. Conclusion: Heliox can rapidly improve ventilation in patients presenting to an emergency department with acute severe asthma with respiratory acidosis and a short duration of symptoms.