ABGs are commonly used to monitor acute respiratory conditions, especially where there is a risk of type 2 respiratory failure (e.g. chronic obstructive pulmonary disease)

Normal values

Terminology

Respiratory failure

• PaO2 is the partial pressure of oxygen, the amount of oxygen dissolved in the blood
• A low PaO2 indicates hypoxia and respiratory failure
• It is important to distinguish the type of respiratory failure:
  • Normal PaCO2 with low PaO2 indicates type 1 respiratory failure (only one is affected)
  • Raised PaCO2 with low PaO2 indicates type 2 respiratory failure (two are affected)
• If a patient is receiving oxygen their pO2 should be approx. 10kPa less than the % inspired concentration FiO2

Acidaemia

• High H+ (low blood pH)
• Leads to acidosis

Alkalaemia

• Low H+ (high blood pH)
• Leads to alkalosis

Compensation

• Aims to correct a pH imbalance

Acid-base balance

Metabolic acidosis

• Occurs when there is an excess of H+ produced by the body due to disease e.g. lactic acidosis, renal failure, sepsis