Respiratory Failure

Respiratory failure is a failure to maintain adequate gas exchange and is characterised by abnormalities of normal arterial blood gases.

Respiratory failure can be acute, acute-on-chronic or chronic.

• Acute hypercapnic respiratory failure – typical asthma attack. ABGs show high PaCO₂, low pH and normal bicarbonate (HCO₃)
• Chronic hypercapnic respiratory failure – history of respiratory disease, high PaCO₂, normal pH, high bicarbonate
• Acute-on-chronic hypercapnic respiratory failure – acute deterioration in an individual with significant pre-existing hypercapnic respiratory failure, high PaCO₂, low pH and high bicarbonate. Typically an exacerbation of COPD.

Type I only PaO₂ is below 8 kPa (hypoxaemia). Likely to be those with asthma, pneumonia, PE (pulmonary embolism), pulmonary oedema and loss of lung volume.

Type I is more typically those who have not got a respiratory disease and have caught pneumonia or something similar. Type II is more likely to be related to chronic patients e.g. COPD.

Type II – PaO₂ low and PaCO₂ is elevated above 6 kPa (hypercapnia). Likely to be exacerbations of COPD, patients with chest wall deformity or NM disease or decompensated sleep apnoea

Causes of hypoxaemia:

·   Hypoventilation (alveolar)

·   Diffusion impairment

·   Shunt

·   V/Q inequality

Causes of hypercapnia:

·   Hypoventilation

·   V/Q inequality

·   In some cases, the use of oxygen therapy

Clinical presentations in respiratory failure are cyanosis, mental confusion, tachycardia, restlessness, tremor, slurred speech, asterixis (flapping tremor) and fluctuations in mood.