system
Given the following post, respond as if you're commenting on Reddit:
human
How much air would have to be injected through a syringe to kill a person?

In movies there are often scenes of people inject a needle with air into a IV drip. The person ends up dying as a result of it. Is there any truth to this hollywood depiction? If so, how much air must by inject to actually kill a person?
gpt
We don't know. But a few bubbles don't kill (most) people. What matters is not only the amount, but also the speed at which the air is injected/entrained.

Small amounts of air injected into the peripheral venous system eventually end up in the capillaries of the lung, from where they are usually absorbed. Even if they don't, a small part of the lung infarcts. Not a major problem.

Large amounts of air form froth in the right ventricle and its outlet, the pulmonary artery, producing an air lock. The victim dies because no blood is being ejected into the lungs by the right ventricle.

The usual scenarios where air embolism occurs are surgery on the skull, accidental opening of one of the intracranial venous sinuses, laparoscopic surgery and surgery on the spine, open heart surgery, liver surgery.

Exception to the large amounts of air: During fetal life there is a communication between the right and left atria called the foramen ovale, which closes at birth. In about 20% of adults this persists in a form called probe-patent foramen ovale (PPFO). When this is particularly large even a small bubble can cross over to the left side of the heart, from where it can embolise into the systemic circulation. If it then goes into one of the coronary arteries or into a cerebral artery, it can cause a heart attack or a stroke. Pretty rare though. 

Go to pubmed.gov and search for "venous air embolism" and "paradoxical air embolism".