HELIOX IMPROVES PULSUS PARADOXUS AND PEAK EXPIRATORY FLOW IN NONINTUBATED PATIENTS WITH SEVERE ASTHMA

Heliox is a blend of helium and oxygen with a gas density less than th at of air that decreases airway resistance (Raw) in patients ventilate d for status asthmaticus. We tested whether breathing an 80:20 mixture of helium:oxygen would reduce pulsus paradoxus (PP) and increase peak expiratory flow (PEF) in patients presenting to the emergency room wi th an exacerbation of asthma. After receiving 30 min of beta-agonist a erosols and intravenously administered methylprednisolone, 27 patients whose PP remained greater than 15 mm Hg and whose PEF remained less t han 250 L/min consented to breathe heliox or room air for 15 min. PP d ecreased and PEF increased with time in control patients, indicating a time-related effect of routine bronchodilator therapy (p < 0.05). PP decreased in 15 of 16 patients during heliox, and the change with heli ox was significantly greater than that during air breathing (p < 0.01) . PEF measured with a Wright's peak flow meter calibrated for heliox i ncreased in all patients breathing heliox. Again, the increase in PEF during heliox breathing was significantly greater than the correspondi ng change in control patients breathing air (p < 0.001). To the extent that PP reflects the inspiratory fall in pleural pressure, this reduc tion in PP indicates a substantial reduction in inspiratory Raw when t he less dense gas is inspired through narrowed bronchi having turbulen t flow regimes. The 35% increase in PEF while breathing heliox signals a similar reduction in expiratory Raw, which might diminish the hyper inflation often observed during an exacerbation of asthma. Taken toget her, these effects of heliox are likely to diminish the tendency to in spiratory muscle fatigue until bronchodilation is effected during init ial treatment of severe asthma.