The study evaluated seven intensive care unit (ICU) ventilators (Veolar FT, Galileo, Evita 2, Evita 4, Servo 900C, Servo 300, Nellcor Puritan Bennett 7200 Series) with helium-oxygen (HeO 2 ), using a lung model, to develop correction factors for the safe use of HeO 2 . A 70:28 helium-O 2 mixture (heliox) replaced air and combined with O 2 (HeO 2 ). Theoretical impact of HeO 2 on inspiratory valves and gas mixing was computed. True fraction of inspired oxygen (F I O2 del) was compared with fraction of inspired oxygen (F I O2 ) set on the ventilator (F I O2 set). True tidal volume (V T del) was compared with V T set on the ventilator (V T set) in volume control and with control V T del at F I O2 1.0 in pressure control. F I O2 del minimally exceeded F I O2 set ( р 5%) except with the 7200 Series (F I O2 del Ͼ F I O2 set by 125%). In volume control, with the Veolar FT, Galileo, Evita 2, and Servo 900C, V T del Ͼ V T set, with the 7200 Series V T del Ͻ V T set (linear relationship, magnitude of discrepancy inversely related to F I O2 set). With the Evita 4, V T del Ͼ V T set (nonlinear relationship), whereas with the Servo 300 V T del ϭ V T set. In pressure control, V T del was identical to control measurements, except with the 7200 Series (ventilator malfunction). Correction factors were developed that can be applied to most ventilators. Tassaux D, Jolliet P, Thouret J-M, Roeseler J, Dorne R, Chevrolet J-C. Calibration of seven ICU ventilators for mechanical ventilation with helium-oxygen mixtures. AM J RESPIR CRIT CARE MED 1999;160:22-32.Reducing the density of inspired gas by using a mixture of helium and O 2 (HeO 2 ) instead of air and O 2 (airO 2 ) can be beneficial in spontaneously breathing patients with upper or lower airway obstructive disease (1, 2). In acute severe asthma, breathing HeO 2 increases peak expiratory flow and Pa O2 , and decreases pulsus paradoxus, Pa CO 2 , and dyspnea (3-5). In patients with COPD, breathing HeO 2 increases expiratory flow and decreases airway resistance (6, 7). Moreover, evidence suggests that these favorable effects can also be obtained during mechanical ventilation in status asthmaticus (8) and in patients with COPD (9, 10), even though the data are still preliminary in the latter patient population, and await confirmation by prospective studies. However, the physical properties of helium could interfere with several key ventilator functions such as gas mixing, inspiratory and expiratory valve accuracy, flow measurement, triggering, positive end-expiratory pressure (PEEP), and automatic leakage compensation, thus raising issues regarding the accuracy of ventilator performance (11) and patient safety.The present study was designed to test the performances of seven standard intensive care unit (ICU) ventilators available in Europe during HeO 2 utilization, compared with theoretical predictions based on the physical properties of helium, and to develop correction factors (12) to ensure the safe use of HeO 2 during mechanical ventilation.
