Hypoxaemia

Hypoxaemia definition

Low oxygen levels in the blood, defined as an arterial partial pressure of oxygen (PaO2) of <80 mmHg.

Causes of hypoxaemia

Common causes include hypoventilation and venous admixture.

What is venous admixture?

The process by which venous blood mixes with arterial blood without proper oxygenation.

Ventilation to Perfusion ratio (V:Q) in healthy lung is?

Normally approximately 1:1.

Parenchymal disease effects on oxygen diffusion

Oxygen cannot diffuse properly due to barriers such as pus, water, or hemorrhage in the lungs.

What happens to PaCO2 during hypoventilation?

Hypoventilation always results in hypercapnia, or elevated levels of PaCO2, regardless of pulmonary function.

Room air composition

Typical composition is 21% oxygen and 79% nitrogen.

Alveolar gas pressures at sea level for Room Air

Water vapour: 50 mm Hg, CO2: 40 mm Hg, Oxygen: 105 mm Hg, Nitrogen: 560 mm Hg.

Effect of reduced ventilation on gas exchange

A decrease in ventilation leads to increased alveolar CO2 and decreased alveolar O2, causing hypoxaemia.

Supplemental oxygen treatment effects on PaO2 and PaCO2

Increasing inspired oxygen can treat hypoxaemia but does not correct the underlying hypoventilation.

What happens to nitrogen and oxygen during 100% oxygen therapy?

Nitrogen decreases and oxygen can theoretically reach a partial pressure of 665 mm Hg.