Qs people asked me on science and my replies to them - part 193

A syringe or IV can accidentally inject air into your veins. Air can also enter your veins or arteries through a catheter that’s inserted into them. Air can enter your veins and arteries during surgical procedures, when they are cut. This is most common during brain surgeries. According to an article in the Journal of Minimal Access Surgery , up to 80 percent of brain surgeries result in an air embolism. However, medical professionals usually detect and correct the embolism during the surgery before it becomes a serious problem.

Doctors and nurses are trained to avoid allowing air to enter the veins and arteries during medical and surgical procedures. They’re also trained to recognize an air embolism and treat it if one does occur.

Lung trauma: An air embolism can sometimes occur if there’s trauma to your lung. For example, if your lung is compromised after an accident, you might be put on a breathing ventilator. This ventilator could force air into a damaged vein or artery.

Scuba diving : You can also get an air embolism while scuba diving. This is possible if you hold your breath for too long when you’re under water or if you surface from the water too quickly. During ascent after scuba diving, where an increase in air volume in the lungs pushes tiny bubbles of air into the bloodstream that expand as you rise.

These actions can cause the air sacs in your lungs, called alveoli, to rupture. When the alveoli rupture, air may move to your arteries, resulting in an air embolism.

Explosion and blast injuries: An injury that occurs because of a bomb or blast explosion can cause your veins or arteries to open. These injuries typically occur in combat situations. The force of the explosion can push air into injured veins or arteries. The most common fatal injury for people in combat who survive blast injuries is “blast lung.” Blast lung is when an explosion or blast damages your lung and air is forced into a vein or artery in the lung.

Blowing into the vagina: In rare instances, blowing air into the vagina during oral sex can cause an air embolism. In this case, the air embolism can occur if there’s a tear or injury in the vagina or uterus. The risk is higher in pregnant women, who may have a tear in their placenta.

Here we need to distinguish between little bubbles and big ones, because they do damage in different ways. Small bubbles can block capillaries in vital organs, most critically the brain, causing anything from pain and inflammation to neurological damage and paralysis. A small bubble impedes blood flow the same way a solid obstruction would — the bubble's surface tension relative to its size is too great for the force of blood to break it up or shove it along. Bad? Yes. Fatal? Probably not, well mostly.

A big bubble, on the other hand, gets us into the vapour lock scenario. Your heart, like the fuel pump in an old car (cars with modern fuel injection work differently), is a simple mechanical device. In ordinary operation, its contracting chambers squeeze the blood out and force it through the circulatory system. All is well. Now imagine a massive air embolus shows up and your heart starts squeezing on that. There's nothing to get any purchase on; the air just compresses. Blood flow stops, and eventually so does your heart.

It also makes a difference where the air bubbles enter. Emboli from injections or IVs are typically confined to veins, but if a bubble ends up in your arteries (which can happen if you have the double misfortune of air in your veins plus a fairly common congenital heart defect), then the bubble can block your coronary arteries or the blood supply to your brain. The former type of blockage, at least, can mean death.
 
How much air is needed to kill you? That's debatable and doubtless varies, but generally speaking, a lot.

A minor air embolism may cause very mild symptoms, or none at all. Symptoms of a severe air embolism might include: difficulty in breathing or respiratory failure, chest pain or heart failure, muscle or joint pains, stroke, mental status changes such as confusion or loss of consciousness, low BP, blue skin hue.

Treatment for an air embolism has three goals:

• stop the source of the air embolism
• prevent the air embolism from damaging your body
• resuscitate you, if necessary

Well trained medical practitioners will know how the air is entering your body. In these situations, they will correct the problem to prevent future embolisms. Your doctor may also place you in a sitting position to help stop the embolism from travelling to your brain, heart, and lungs. You may also take medications, such as adrenaline, to keep your heart pumping.

If possible, your doctor will remove the air embolism through surgery. Another treatment option is hyperbaric oxygen therapy. This is a painless treatment during which you occupy a steel, high-pressurized room that delivers 100 percent oxygen. This therapy can cause an air embolism to shrink so it can be absorbed into your bloodstream without causing any damage.

Q: What happens if you inject air into your muscle along with medicines?

But large amounts of air can be dangerous.

If you put in a few milliliters it will track between muscle fibres mostly and you might feel a “crackling” sensation of the bubbles being squeezed through tissue gaps when you press or contract the muscle.

 A few things could happen with large amounts of air in your muscles, according to doctors ....

1. the gas is retained within the muscle. If there is much gas the pressure will greatly increase as the muscles are contained within fascial compartments causing a “compartment syndrome” where the pressure stops blood entering the compartment and the contents hence start to die. This can be very painful and cause damage to nerves and muscle death, releasing breakdown products that can cause problems for the kidneys and heart, even potentially leading to complete kidney failure or fatal cardiac complications.
2. More likely, the gas will track back along the needle track once pressures in the muscle are high. There are many veins in the muscle (some too small to see with the naked eye) so you will have passed through many with the needle. The air will pass into the circulation through these (because of the very low viscosity or air large amounts can pass through even a tiny hole in a vessel. IF your heart is normal and you are healthy you can tolerate around 1ml of air in the heart per kg of body weight. Below this your heart will pump the gas into the lung circulation and At around this amount a rapid air infusion into a vein and then to the heart can interfere with heart function enough to threaten your life. IF your heart is impaired a lesser amount of gas could kill you. IF you have a structural anomaly with your heart (small ones might not even otherwise affect you and not be known about) and the gas passes into your systemic circulation (to your body instead of your lungs), then some might pass into the brain circulation and especially if you are upright rise to the top and force the blood out of the vessels in your head leading to ischaemia, which might be transient and make you collapse, though could also cause a stroke or even death.