Hypoxaemia: Reversible Causes of Cardiac Arrest

What is Hypoxaemia?

Hypoxaemia is the reduction in the values for partial pressure of oxygen dissolved in arterial blood (PaO2) and arterial oxygen saturation (SaO2) (Bullock & Hales 2013). Pa02 is best measured by arterial blood gas (ABG) analysis, while SaO2 can be routinely assessed using a non-invasive test called pulse oximetry.

During clinical assessment, hypoxaemia should be considered if a patient has a respiratory rate greater than 24 per minute, and arterial oxygen saturations (SaO2) below 94% on room air (Rittayamai et al. 2015). Clinically, however, hypoxaemia is defined as: PaO2 < 8 kilopascals (kPa), or 60 millimetres of mercury (mmHg), on ABG (Bullock & Hales 2013).

The degree of hypoxaemia is reflected in the PaO2 value. There is no standardisation of hypoxic thresholds (Allwood et al. 2018), however they are commonly divided into three categories:

• Mild hypoxaemia
• Moderate hypoxaemia
• Severe hypoxaemia