5-high VQ= dead space

KYJ5 - Dead space.
Knowing you Jargon
Previously, we covered VQ mismatch with low VQ otherwise called "shunt".

This episode we look at its opposite.  High VQ is called dead space.

Dead space refers to a disproportionately high volume of air to blood ratio in the lungs.

In respiratory presentations where a lung can ventilate or fill with air, but a vascular obstruction has occurred, the air doesn't have an opportunity to
Give up oxygen or diffuse CO2.

Such a condition is seen in a pulmonary embolism (PE).  Due to a blood clot obstructing a segment of pulmonary vessels, blood can't flow through lobules or segments of lung.  Air in these sections ventilate well enough, but with no blood flow, there is no diffusion.  These patients are said to
Have a high VQ or dead space.

VQ is usually 4l air : 5 l blood
Making a VQ ratio of 0.8.

If I reduce (block) blood flow I might see a High VQ of 4l air :3l blood or a VQ = 1.33
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Less blood perfusing lung = lower oxygen in blood (Hypoxaemia) and high CO2 ( hypercapnoea).

This leads first to a Respiratory acidosis then a mixed metabolic  acidosis as hypoxic cells start enter anaerobic metabolism and produce Lactic Acid.

Treatment of High VQ or Dead space is to, oxygenate optimally, and restore blood flow.

Empirically, anticoagulants were used, typically Heparin. Prior to
This regimen, 30% of PE patients died, but with anti coagulation the mortality is less than 9%.

Improvements currently available include thrombolysis. Where a plasminogen activator is administered to encourage the patients own enzyme system to seek and dissolve the fibrin clot.

Improvements in testing and diagnosis also reduces ischaemia time, which is the ultimate goal.
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