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:
- Increases delivery of FIO2
- Reduces entrainment of room air
- 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.
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.
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).
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