12th January 2024

Types and Pathophysiology

Respiratory failure is generally categorised into two types depending on the underlying pathophysiology and subsequent arterial blood gas picture.

Type 1 Respiratory Failure

When blood flows through a diseased part of the lung (e.g. asthma, pneumonia) with impaired ventilation, it results in hypoxic and CO2-rich blood entering pulmonary veins. Increased ventilation of neighbouring regions of normal lung can increase CO2 excretion but cannot augment oxygen uptake as the haemoglobin flowing through these normal regions is already fully saturated.

Hence, blood coming from normal and under-ventilated areas results in hypoxia with normocapnia, leading to Type 1 respiratory failure.

Type 2 Respiratory Failure

This happens when there is not sufficient normal lung left to correct PaCO2, leading to severe ventilation – perfusion mismatch. Seen in conditions that cause generalised reduction in total ventilation, including diseases of the lung as well as neuromuscular disorders.