VQ Ratio

Question 1

Dependent and Non-Dependent region of lungs

Answer 1

The non-dependent region on the lung (upper) are already inflated due to the weight of the hanging lung.

The dependent region (lower) is better ventilated as the air takes the path of least resistance. Intrapleural pressure is less negative in the lower region and has greater potential for increased ventilation.

In mechanical ventilation, the air takes the path of least resistance which is the upper part and the lower part is prone to collapse - also absorption atelectasis occurs at higher o2 concentrations (less gas enters the alveoli than is being removed by the blood). There cannot be a VQ match in mechanical ventilation.

Question 2

What is VQ matching?

Answer 2

For gas exchange to occur, ventilation (V) and perfusion (Q) need to be in the same place at the same time.

Perfect match 1/1. Normal blood gases achieved with 0.8/1.

Question 3

Abnormal ventilation/perfusion

Answer 3

• Atelectasis (collapse of the alveoli)
• Consolidation (filling of the alveoli)
• Pulmonary embolus (blockage in the capillaries)

Question 4

How can positioning help VQ?

Answer 4

• Maximises ventilation (more space for the lungs to expand)
• Maximises diaphragmatic function (lower hemi-diaphragm is already pre stretched)
• Decrease WOB
• Drain sputum