What are the key clinical features that differentiate between Type 1 and Type 2 respiratory failure in adults?

Type 1 respiratory failure is characterised by hypoxaemia (low blood oxygen levels) without hypercapnia (normal or low carbon dioxide levels). It typically results from conditions causing impaired oxygen exchange such as pneumonia, pulmonary oedema, or acute respiratory distress syndrome. Clinically, patients may present with breathlessness, increased respiratory rate, and use of accessory muscles of respiration, but carbon dioxide retention is not a feature.

Type 2 respiratory failure involves both hypoxaemia and hypercapnia (elevated arterial carbon dioxide levels), indicating ventilatory failure. It is commonly seen in conditions causing alveolar hypoventilation such as chronic obstructive pulmonary disease (COPD), obesity hypoventilation syndrome, or neuromuscular disorders like motor neurone disease. Clinical features include breathlessness, shallow breathing, use of accessory muscles, daytime sleepiness, morning headaches, confusion, and signs of CO2 retention such as abdominal paradox and poor concentration.

In summary, the key differentiating clinical feature is the presence of hypercapnia in Type 2 respiratory failure, reflecting ventilatory failure, whereas Type 1 respiratory failure is characterised by isolated hypoxaemia due to oxygenation failure without CO2 retention.

These distinctions guide management decisions including the use of non-invasive ventilation, which is particularly relevant in Type 2 respiratory failure to support ventilation and reduce CO2 levels.

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