Respiratory failure

• Defined when the PaO2 is <8kPa
• Divided into 2 types;
  • Type I
    • Defined as a hypoxia with a normal or low CO2
    • Caused primarily by ventilation/perfusion (V/Q)mismatch
    • Causes;
      • Pneumonia
      • Pulmonary oedema
      • PE
      • Asthma
      • Emphysema
      • Fibrosing alveolitis
      • ARDS
  • Type II
    • Defined as a hypoxia with a hypercapnia (PaCO2 >6kPa)
    • Caused by alveolar hypoventilation with or without V/Q mismatch
    • Causes;
      • Pulmonary disease – asthma, COPD, pneumonia, pulmonary fibrosis, obstructive sleep apnoea
      • Reduced ventilatory drive – sedative drugs, CNS tumour or trauma
      • Neuromuscular disease – cervical cord lesion, diaphragmatic paralysis, paralytic poliomyelitis, MG, Guillain-Barre syndrome
      • Thoracic wall disease – flail chest, kyphoscoliosis

Clinical features of hypercapnia;

• Headache, peripheral vasodilation, tachycardia, bounding pulse, tremor/flap, papilloedema, confusion, coma

Clinical features of hypoxia

• Dyspnoea, restlessness, agitation, confusion, central cyanosis, if long standing – polycythaemia, pulmonary hypertension, cor pulmonale

Investigations

• Bloods – FBC, U&Es, CRP, ABG
• Radiology – CXR
• Microbiology – bloods and sputum
• Spirometry – COPD, neuromuscular disease, Guillain-Barre syndrome

Management

• Type I
  • Treat underlying cause
  • Give oxygen 35-60% by face mask
  • Assisted ventilation if PaO2 <8kPa despite 60% O2
• Type II
  • Treat underlying cause
  • Controlled O2 therapy start at 24% O2
  • Recheck ABG after 20mins. If PaCO2 is the same of lower increased O2 to 28% if PaCO2 has risen >1.5kPa ad the patient is still hypoxic consider a respiratory stimulant Doxapram
  • If this fails consider intubation and ventilation