Noninvasive ventilation (NIV) improves oxygenation

Michael Allison, MD
27th Feb 2021

The first way noninvasive ventilation (NIV) can help patients with pulmonary disease is through improvements in oxygenation (the other, is by improving ventilation).

There are three main ways by which NIV improves oxygenation:

  1. Increases delivery of FIO2
  2. Reduces entrainment of room air
  3. Improves the ventilation/perfusion (V/Q) ratio or V/Q matching


1. NIV increases the delivery of FIO2

The NIV ventilator and interface allow for an increased, and more accurate, delivery of FIO2 compared to a traditional oxygen mask. 


2. NIV reduces entrainment of room air

With nasal cannulas and traditional oxygen masks, the loose fit allows patients to breathe in ambient air. This means the amount of oxygen delivered is being diluted by the presence of room air entrainment. The tight fit of the NIV mask prevents the entrainment of room air into the breathing circuit.

 Women wearing traditional oxygen mask and noninvasive ventilation mask showing the difference in air flow. Illustration.

Figure 1. The masks used in noninvasive ventilation (NIV), compared to nasal cannulas or traditional oxygen masks, prevent the entrainment of room air.

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3. NIV improves ventilation/perfusion (V/Q) ratio or V/Q matching

Patients with lung diseases may have atelectasis, or collapsed areas of the lung, that don’t effectively participate in gas exchange. By providing a positive pressure to the lungs, these areas can re-expand and allow oxygen from the airways to diffuse into the pulmonary circulation.

Figure 2. The effects of noninvasive ventilation (NIV) on regions of atelectasis. Before NIV the alveoli are collapsed and don't participate in gas exchange. After NIV, these areas can expand and allow the diffusion of oxygen into the pulmonary circulation.

This results in better ventilation and perfusion matching, also known as ventilation/perfusion (V/Q) matching. Ventilation, V, is a measure of the amount of air that reaches the alveoli, and perfusion, Q, is a measure of the amount of blood within the capillaries surrounding the alveoli. After NIV, more air can reach the alveoli, increasing the V/Q ratio. 

By improving V/Q matching through recruiting atelectatic lung regions and allowing a reliable delivery of set FIO2, NIV can improve the oxygenation of patients with hypoxic respiratory failure (HRF).

Alveoli and lung capillaries showing the effect of noninvasive ventilation on the ventilation-perfusion ratio in lung disease. Illustration.

Figure 3. The effects of noninvasive ventilation (NIV) on the ventilation/perfusion ratio (V/Q) in lung disease. NIV increases the V/Q ratio (V/Q matching) of areas of atelectasis, resulting in increased oxygenation of the lungs.

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Recommended reading

  • Kallet, RH, and Diaz, JV. 2009. The physiologic effects of noninvasive ventilation. Respir Care. 54: 102–115. PMID: 19111110