Question

Capnography is the clinical measurement of expired carbon dioxide. When healthcare providers give CPR (cardiopulmonary resuscitation), they are compressing the heart to pump blood through the body because the heart has lost the ability to successfully do this on its own. Capnography is often used to measure the effectiveness of CPR, with low expired Carbon dioxide values indicating ineffective chest compressions. Why would low expired carbon dioxide levels indicate ineffective compressions?

Answer 1

Respiration is the by which the CO₂ in our body exited which the help of blood as the deoxygenated blood carries CO₂ to the lungs. In this case a person lost his ability of pumping blood to various parts of the body by his heart. Hence heart also lost the ability to pump deoxygenated blood to the lungs where the gaseous exchange takes place. This patient has given CPR treatment where the compressions are responsible for regaining the heart's ability to pump blood to various parts of the body.

Whenever effective chest compressions exist the heart pumps the normal volume of blood to the lungs and there through diffusion normal volume of CO₂ moves out.

But whenever the ineffective chest compressions exist the heart cannot pump deoxygenated blood maximum to its capacity. Hence our body cannot remove maximum CO₂. The diffusion of carbon dioxide out is much lower when compared to that when effective chest compressions exist.

This is why the low expired carbon dioxide levels indicate infective compressions.