Respiratory failure

• Respiratory failure occurs when there is a failure of gas exchange and/or ventilation, leading to abnormalities in arterial oxygen partial pressure (PaO2) and arterial carbon dioxide partial pressure (PaCO2) on arterial blood gas.
• Type 1 respiratory failure definition:

  • Hypoxaemia (PaO2 <8 kPA) WITH
  • Normocapnia (PaCO2 <6.0 kPA)
• Type 2 respiratory failure failure definition:

  • Hypoxaemia (PaO2 <8 kPa) WITH
  • Hypercapnia (PaCO2 >6.0 kPa)
• Type 1 respiratory failure:

  • Usually occurs due to ventilation/perfusion mismatch
  • As a result of the V/Q mismatch - PaO2 falls and PaCO2 rises. Rise in PaCO2 rapidly triggers an increase in a patient's overall alveolar ventilation which corrects the PaCo2 but not the PaO2
• Type 1 respiratory failure causes:

  • Reduced ventilation and normal perfusion = pneumonia, pulmonary oedema, bronchoconstriction
  • Reduced perfusion with normal ventilation = pulmonary embolism
• Type 2 respiratory failure:

  • Occurs as a result of alveolar hypoventilation, which prevents patients from being able to adequately oxygenate and eliminate CO2 from their blood
  • PaO2 falls due to lack of oxygenation
  • PaCO2 rises due to lack of ventilation and elimination of CO2
• Type 2 respiratory failure causes:

  • Increased resistance due to airway obstruction e.g. COPD
  • Reduced compliance of the lung tissue/chest wall e.g. rib fractures, obesity
  • Reduced strength of the respiratory muscles e.g. GBS, motor neurone disease
  • Reduced respiratory drive e.g. opioids and other sedatives