Oxygen therapy

Question 1

What does a low-flow (variable performance) mask do?

Answer 1

Provide only a proportion of the patient’s inspired gas. They deliver a flow rate that is less than the patient’s peak inspiratory flow (PIF) so that room air is sucked in through holes in the mask to dilute the oxygen. The fraction of inspired oxygen (FiO2) is then dependent on the patient’s ventilation rate. The more rapid the patient’s ventilation, the more room air is entrained and the lower the FiO2.

Question 2

What does a high-flow (fixed performance) mask do?

Answer 2

Venturi masks deliver a prescribed gas mixture at flows intended to be greater than demand, i.e. higher than the patient’s PIF. Oxygen rushes from a nozzle and entrains a proportion of room air through a fixed size entrainment port, so that a specific concentration is delivered.

Question 3

What are the benefits of a nasal cannula and which pts are they best used for?

Answer 3

Deliver oxygen directly into the nostrils so that the patient can talk, cough, eat and drink. 80% of the oxygen is wasted. They are useful for people who find a mask uncomfortable, or who require long-term oxygen