Anaesthesia Fundamentals | Physiology | Ventilation/Perfusion Abnormalities

Ventilation/Perfusion Abnormalities
Session Overview
Description
This session describes how and why ventilation and perfusion vary in the healthy lung. Causes of hypoxia, such as hypoventilation, increased dead space and shunt, are discussed to help the trainee explain and manage hypoxia clinically.

Learning Objectives
By the end of this session you will be able to:

• Describe and explain the normal distribution of ventilation and perfusion in the lung
• Describe the shunt equation
• Explain the effect of the following on the partial pressure of oxygen and carbon dioxide in arterial blood: hypoventilation, increase in dead space, increase in the degree of shunt

Prerequisites
Before commencing this session you should complete:

• Gaseous Exchange: O2 and CO2 Transport (001-0660)
• Gaseous Exchange: Hypoxia and Hyper and Hypo-capnia (001-0661)
• Function of Haemoglobin in Oxygen Carriage (001-0663)
• Pulmonary Ventilation: Volumes, Flows, Dead Space & Preoxygenation 1 (001-0665)
• Pulmonary Ventilation: Volumes, Flows, Dead Space & Preoxygenation 2 (001-0666)

In an ideal lung model, ventilation () and perfusion () would be perfectly matched. In the healthy lung however, the ventilation/perfusion (/) ratio varies. There are a number of reasons for this variance, which are explained in this session.

Understanding the normal physiology is essential in order to explain how changes in the degree of shunt or dead space affect arterial blood gases.

The implications of these abnormalities in terms of the process of diseases and their management should then be easier to understand.