Suppose a patient has a ventilation of 10L per minute, a tidal volume of 500ml, a respiratory rate of 20/min, an inspiratory time (IT) of 1 second, an expiratory time (ET) of 2 seconds, and a nasal cannula supply of 6L/ Min, the volume of the anatomical storage chamber is 50ml, and the most 1.5 times of ET can exhale most of the tidal volume. After 0.5 seconds, the gas storage chamber can be filled with oxygen 50ml, inhaled for 1 second, the inhalable gas is 500ml, and the oxygen is inhaled:
50ml + 100ml + 350ml×0.2 = 220ml
(Air chamber volume) （Nasal tube flow/second) (Inhaled air oxygen content) (Total amount of oxygen inhaled)
It can be seen from the above calculation that oxygen is absorbed by the nasal cannula, and when the oxygen flow rate is 1 to 6 L, the FiO2 can be increased by 4% for each 1 L/min increase.
Inhaled oxygen concentration = 21 + 4 * flow rate * oxygen concentration (90-4) / 100