The effect of helium on ventilator performance - Study of five ventilatorsand a bedside pitot tube spirometer

Objective: To assess in vitro the performance of five mechanical ventilator s-Siemens 300 and 900C (Siemens-Elma; Solna, Sweden), Puritan Bennett 7200 (Nellcor Puritan Bennett; Pleasanton, CA), Evita 4 (Dragerwerk; Lubeck, Ger many), and Bear 1000 (Bear Medical Systems; Riverside CA)-and a bedside sid estream spirometer (Datex CS3 Respiratory Module; Datex-Ohmeda; Helsinki, F inland) during ventilation with helium-oxygen mixtures. Design: In vitro study. Setting: ICUs of two university-affiliated hospitals. Methods and measurements: Each ventilator was connected to 100% helium thro ugh compressed air inlets and then tested at three to six different tidal v olume (VT) settings using various helium-oxygen concentrations (fraction of inspired oxygen [FIO2] of 0.2 to 1.0) - FIO2 and VT were measured with the Datex CS3 spirometer, and VT was validated with a water-displacement spiro meter. Main results: The Puritan Bennett 7200 ventilator did not function with hel ium. With the other four ventilators, delivered FIO2 was lower than the set FIO2. For the Siemens 300 and 900C ventilators, this difference could be e xplained by the lack of 21% oxygen when helium was connected to the air sup ply port, while for the other two ventilators, a nonlinear relation was fou nd. The VT of the Siemens 300 ventilator was independent of helium concentr ation, while for the other three ventilators, delivered VT was greater than the set VT and was dependent on helium concentration. During ventilation w ith 80% helium and 20% oxygen, VT increased to 125% of set VT for the Sieme ns 900C ventilator, and more than doubled for the Evita 4 and Bear 1000 ven tilators. Under the same conditions, the Datex CS3 spirometer underestimate d the delivered VT by about 33%. Conclusions: At present, no mechanical ventilator is calibrated for use wit h helium. This investigation offers correction factors for four ventilators for ventilation with helium.