Oxygenation in status asthmaticus improves during ventilation with helium-oxygen

Objectives: To determine the effect of breathing helium-oxygen (HELIOX) mix tures on pulmonary gas exchange during severe asthma. Design: A retrospective case-match control design was used to compare the c hanges in alveolar to arterial gradient [(A-a)gradient] in the first 2 hrs of mechanical ventilation (MV) for status asthmaticus (SA) in patients who received HELIOX with those who did not. Patients were matched for diagnosis of asthma, ventilatory failure, ventilator mode and settings, and equivale nt pharmacologic therapy, Setting: The adult and pediatric intensive care units of a tertiary-care ho spital. Subjects: Adult and pediatric patients undergoing MV for SA. Interventions: Use of HELIOX or standard nitrogen-oxygen mixtures during MV . Measurements and Main Results: A total of 11 patients receiving HELIOX in t he first 2 hrs of MV for SA were compared with 11 case-matched controls who did not. At baseline, the HELIOX and control groups had similar (A-a)gradi ents (216 +/- 92 torr and 226 +/- 82 torr, respectively). The (A-a)gradient decreased significantly to 85 +/- 44 torr after initiation of ventilation with HELIOX (p < .0003), whereas it did not change significantly in the con trol group in a similar time frame and during identical treatment without H ELIOX, The reduction in (A-a)gradient in the HELIOX group facilitated a red uction in FIO2 from 0.8 +/- 0.2 initially to 0.4 +/- 0.1 at the time of the second blood gas determination, thus permitting greater concentrations of helium to be administered. Conclusions: MV with HELIOX improves (A-a)gradient in patients with SA. Alt hough this improvement adds little to routine therapy with supplemental oxy gen, it does permit reduction in concentration of inspired oxygen to levels that maximize helium concentration and thus permit full benefits of HELIOX on lung mechanics to be realized in even the most severely ill asthmatics.