Heliox delivery with noninvasive positive pressure ventilation: a laboratory study.
BACKGROUND
There is clinical interest in the use of heliox (helium-oxygen mixture) during noninvasive positive pressure ventilation (NPPV), but delivery of heliox with ventilators designed for NPPV has not been reported. We studied helium concentration ([He]) when an 80%:20% helium:oxygen mixture (heliox) was used with 5 NPPV ventilators (Knightstar, Quantum, BiPAP S/T-D30, Sullivan, and BiPAP Vision).


METHODS
A simulated spontaneous breathing lung model was connected to the ventilators with a circuit incorporating a standard leak. Heliox flows of 0, 5, 10, and 18 L/min and oxygen flows of 0 and 10 L/min were titrated into the system at either a proximal position near the lung model or a distal position near the ventilator (titration method). Because the BiPAP Vision has an oxygen delivery module, it was also studied using heliox connected to the air inlet of an oxygen blender, with the blender outlet connected to the oxygen module of the ventilator (blender method). All ventilators were evaluated in spontaneous/timed mode at inspiratory/expiratory pressures of 10/5, 15/5, and 20/5 cm H(2)O. After 5 minutes, [He], oxygen concentration, and pressure in the lung model were recorded.


RESULTS
Heliox flow, NPPV settings, site of heliox infusion, and type of ventilator significantly (p < 0.05) affected [He]. [He] was > 60% when heliox flow was 18 L/min in some combinations of settings. The BiPAP S/T-D30 and Quantum occasionally functioned erratically. The BiPAP Vision (blender method) ventilator performed erratically with heliox unless the exhalation port test was bypassed on startup. The addition of heliox flow had no important effect on inspiratory or expiratory positive airway pressure on those breaths during which the ventilators functioned correctly.


CONCLUSIONS
Heliox flow was the most important determinant of [He] when using heliox with NPPV. With heliox there was a potential for ventilator malfunction in some conditions. The clinical implications of these findings remain to be determined.
Department of Respiratory Care, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA.
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Chatmongkolchart
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Kacmarek
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Hess
D006371:Helium / Q000008:administration & dosage*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D010100:Oxygen / Q000008:administration & dosage*; D011175:Positive-Pressure Respiration; D012122:Ventilators, Mechanical
D006371:Helium; C038949:heliox; D010100:Oxygen