[The effect of helium on ventilator parameters: in vitro study with a Servoi ventilator]. / Efecto del helio sobre los parámetros de los respiradores en ventilación mecánica: estudio in vitro con el respirador Servoi.

ABSTRACT

OBJECTIVE: To analyze the changes in respiratory parameters in a Servoi ventilator with heliox. MATERIAL AND METHODS: In vitro study with a Servoi (Maquet) ventilator in volume controlled (VC), pressure controlled (PC) and volume control regulated by pressure (VCPR) modes connected to an artificial lung. A heliox tank with a fixed concentration of helium 70 % and oxygen 30 % was connected to the air inlet of the ventilator. The ventilator was set in VC mode with tidal volumes of 30, 50, 100, 250 and 500 ml; in PC mode with pressure of 20 and 30 cmH(2)O and in VCPR mode with tidal volume of 150 ml. In each case FiO(2) of 21, 30, 40, 50, 60, 70, 80, 90 and 100 % was used. The FiO(2), inspired and expired tidal volume and inspiratory pressure measured by the ventilator and a pitot spirometer (Datex_S5) were compared. RESULTS: In VC and VCPR modes the increase in helium produced a progressive decrease in the pressure needed to administrate the set volume. Heliox also produced a decrease in the tidal volume measured by the spirometer and the tidal expired volume measured by the respirator. In PC mode, heliox produced a progressive increase in the inspired tidal volume, increasing the differences between inspired and expired tidal volumes. CONCLUSIONS: Heliox used with Servoi ventilator produces a decrease in inspiratory pressures in VC and VCPR modes, and an increase in inspiratory tidal volume in PC mode. In all modes heliox reduced the expired tidal volume measured by the ventilator and the spirometer. These changes should be borne in mind if heliox is used with this ventilator.