A simple model is used to demonstrate the performance of various oxygen delivery devices over a range of ventilatory patterns.
This model was created by attaching a mannequin's trachea to one compartment of a two compartment lung model. The second compartment was used to drive the system at respiratory rates (RR) of 10, 18, and 26. For each RR, tidal volume was driven at 300 mL, 400 mL, and 500 mL in a sine wave flow pattern. Flow was varied to achieve an I:E ratio of 1:1, 1:2, and 1:3 for each tidal volume. Tidal volume, RR, and I:E ratio were measured in the trachea using a fixed orifice pneumotachometer. An air-entrainment mask (AEM) was placed on the mannequin and the FIO2 was measured mid-trachea using a galvanic oxygen analyzer. The gasses were expelled 20 feet away from the model. The FIO2 on the AEM was set at 24%, 35%, 45%, and 55%. The litter flow of oxygen to the mask was set according the manufactures recommend. The FIO2 was also measured at the mask while placed on the mannequin without respirations.
The range of FIO2 measured at each setting without respirations were 25%–26%, 35%–36%, 41%–42%, 52–54%. When peak flow < 30 L/min, the FIO2 measured in the trachea for each of the settings were 26%, 35%, 42%, and 51%. When peak flow was > 40 L/min, the FIO2 measure in the trachea for each of the settings were 26%, 31%, 38%, and 44%.
Tracheal FIO2 was comparable to mask FIO2 when peak flows were less than total flow from the AEM. When peak flows exceed the total flow the tracheal FIO2 decreased below set FIO2 due to the entrainment of additional room air.
This simple model appears to accurately predict FIO2 changes of fixed and variable performance masks and may be used as an educational model to enhance student learning.
David Vines, No Financial Disclosure Information; No Product/Research Disclosure Information