Should the hole of a needle be facing up or down when injecting?
Bevel up. The bevel is an angled shape at the tip. Bevel up means the angle of the cut in the metal, which is about a 30° angle, is oriented upward.It assists the puncture if the sharp hits first, with the remainder of the needle passing soon after, but not letting the person pull away from the pain of the sharpness, too quickly for the needle to penetrate. In the case of venipuncture, not just intramuscular, subcutaneous or intradermal shot, the needle has to get far enough under to reach blood flow, but not too far where the back of the blood vessel is passed all the way through. This means that it’s a finer finesse technique then just lancing an abscess or shoving a “shiv” in a prison yard melee. The tendency of veins to roll when a needle is pushed against them means the best phlebotomy method involves a quick poking motion, albeit with limited thrust so that if a flash of blood appears in the syringe, the forces are halted in time to keep the tip inside the interior of the vessel. If it is a blood draw for lab specimens, the vaccutainer tube is engaged, and the vacuum effect will assist blood flow. If it is an intravenous catheter, great care to hold the needle stable, while advance of the plastic hollow catheter over the needle sheath up into the vessel, then keeping blood access until I.V. fluids are successfully flowing into the system without either a puddle of fluid on the floor around the missed connection or in a bubble under the skin near the site.
What happens if you inject air into your muscles?
I agree that a little bit will do no harm and you won’t really notice much.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.if you put a large amount of air in it is much more dangerous. A few things could happen: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.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.I hope this answer informs you as to how dangerous injecting a large amount of air into you can be!
Is injecting an empty syringe dangerous?
Short answer: No If you have accidentally injected empty syringe nothing would happen so relax, there's nothing to worry about. However its not advisable to do so :p.Air is only dangerous when it enters the vein. When empty syringe is injected,air enters the circulatory system and causes a condition called as "air embolism".When reasonably high amount of air enters the blood stream fast,the bubbles(Embolism) can block major vessels.If it occur in brain,leads to stroke;in heart,causes heart attack.But usually,such air reaches lung ,and get cleared.Problem arises when lung is bypassed somehow. So, yes you can die if air gets in your blood stream BUT you would need more than a full syringe of nothing but air.
Why do doctors squirt some of the liquid out when they have the needles?
To remove air bubbles