The inspired oxygen concentration from pressure limited ventilators with a Venturi air mix rises steeply when the inflating pressure exceeds approximately 8 cm. A mean oxygen concentration of 82% was obtained when a lung model (compliance 0.032 liter/cm) was ventilated with a tidal volume of 0.8 liter. Concentrations of 93% and 61% were delivered when a main line nebulizer was incorporated and driven by a flow of 8 liters of oxygen or air, respectively. Thirty percent to 50% oxygen was obtained only by powering the ventilator by compressed air, and adding oxygen at increasing flows via the main line nebulizer. For volume limited ventilators a graph is shown to predict inspired oxygen. Its validity is dependent upon accurate stroke volume calibration and flowmeters, particularly with the small volumes and flows used in children.
Pontoppidan H, Berry PR. Regulation of the Inspired Oxygen Concentration During Artificial Ventilation. JAMA. 1967;201(1):11-14. doi:10.1001/jama.1967.03130010037008