Effect of helium-oxygen (heliox) gas mixtures on the function of four pediatric ventilators

OBJECTIVETo evaluate the effects of helium on the function of four ventilators commonly used in pediatricsthe Bird VIP, Bird VIP Gold, Servo 300, and Servo 900C. DESIGNProspective setting. SETTINGResearch laboratory at a university hospital. SUBJECTSHelium was administered as an 80:20 mixture of helium-oxygen through the air inlet of the ventilator. Delivered fraction of inspired oxygen (Fio2) was compared with the Fio2 set on the blender dial. Inspiratory displayed tidal volume was recorded as an indicator of what the ventilator “believed” it had delivered and was compared with the VT displayed during ventilation with 100% oxygen (control). Actual delivered VT was measured by a Neonatal Bicore connected to the side port of a “bag-in-box” spirometer, making measurements independent of inspired gas properties, and was compared with VT delivered during ventilation with 100% oxygen. INTERVENTIONSFive gas mixtures were evaluatedFio2 = 0.2, 0.4, 0.6, 0.8, and 1.0 (balance helium). MEASUREMENTS AND MAIN RESULTSDelivered Fio2 was less than set Fio2 on the Servo 900C and VIP ventilators. VT displayed was minimally altered by helium during volume-controlled ventilation but substantially decreased during pressure-controlled ventilation, particularly with the Bird ventilators. During volume-controlled ventilation, VT delivered was substantially increased by helium with the Bird and, to a lesser degree, the Servo 900C ventilators. In contrast, VT delivered decreased slightly in helium with the Servo 300. The same pattern, but with a decreased magnitude, was observed for VT delivered during pressure-controlled ventilation. CONCLUSIONSThe addition of helium has a significant effect on Fio2 delivery, displayed inspiratory VT, and actual delivered VT during both volume- and pressure-controlled ventilation in four ventilators commonly used in pediatric critical care. These effects are both ventilator specific and ventilation mode specific, mandating vigilance during helium ventilation in clinical practice.