When to offer first-aid
Before you go rushing in to help someone, even a friend or family remember, you have to ensure that there isn’t something else you need to deal with first. In a defensive situation you will have to pry your attention away from a person screaming in pain to make sure that no other human threats are present. Only go to help someone once you’re sure that the area is safe and that you can reach the person without becoming injured yourself!
How to treat the wound
Stabbing wounds can be extremely tricky depending on where and how the person is stabbed. If the stab is shallow, a simple cleaning of the wound and a sterile bandage might be all they need. However, a wound that punctures a lung or slices through the liver is immediately life threatening, and is beyond the scope of general first-aid. Therefore, these instructions can help completely treat a minor stab wound, but are limited to merely keeping a seriously stabbed person alive awhile longer until trained medical help arrives, if it is available.
Inspect the patient, and determine the extent of their injuries. Unless the person was caught unawares, they may have multiple stabs and slashes on their body, or clothing may obscure any wounds at all. Part clothing, and look for all wounds before starting your treatment unless there is an obviously serious wound that need immediate treatment (massive amounts of blood, particularly if it is spurting out like a geyser should be treated as quickly as possible!)
Apply a facemask and sterile gloves if possible. At the very least, disinfect your hands. Before the modern world of antibiotics and advanced medicine, battlefields killed men by the thousands through infection. Your hands need to be clean and your mouth should be kept away from the wound to reduce the chances of infection in a world without easy access to antibiotic medicines.
If the person is conscious, begin working but also talk with them. They probably won’t feel much pain to help you know where wounds are, but talking helps keep the person calm and slows heartrate. If any wounds are particularly nasty (say, a knife sticking out of their leg) keep their eyes averted so they don’t focus on it.
If present, leave the weapon in the body. This reduces bleeding and keeps you from accidentally cutting any more vessels when it is removed. Don’t jostle it when helping, and if you move the patient have someone to steady it and keep it from moving. Weapons left in the body should only be removed by knowledgeable medical staff that can immediately perform needed surgery to correct potential damage.
Choose the wound that is bleeding the most and stanch the flow. Any wound where blood is spurting out has priority unless there is serious flow elsewhere, since spurting blood comes from an artery that your body desperately needs. A tourniquet may be needed if there are multiple serious wounds, but it is always better to apply direct pressure instead since that actually stops bleeding rather than cutting off blood flow. Keep a barrier between yourself and the patient’s blood. If you lack gloves, use layers of clean cloth. If you have helpers, clean their hands and let them apply the pressure so you can continue directing things.
Proceed to stanch bloodflow from each major wound, if there are more than one. If possible, have the person sit up and lift limbs above where the heart would be to slow bloodflow. If the wounds are mainly in the legs, lay the patient flat and lift their legs up on a chair or box.
Once you have some control over the bleeding, begin cleaning the wounds in order from most serious to least serious. Remove debris if present, but remember that even a wound without debris has had a dirty sharp implement jab at it, so they all need cleaning. Clean water is the best for sheer irrigation, but in a pinch peroxide or even alcohol will work. As salt is an excellent natural cleanser, a mix of 1 tablespoon of salt to 1 cup of warm clean water is perfect here. Be aware that there will be pain when applying cleaning liquids, so if the person is somewhat conscious give them warning.
Once a wound is clean, close smaller gaping wounds. Butterfly bandages can obviously help here if they are the correct size. Otherwise, glue (on the outside of the wound only!) and duct tape can make an effective placeholder. You want to close the wounds to prevent infectious materials from getting inside, and to keep the wound fairly dry.
If a larger wound refuses to stop bleeding, DO NOT CLOSE IT. Instead, pack it with clean rags and cover with tape. The tape should be reasonably loose: it is primarily a strong covering, not a wound binder, and you want to be able to change out the rags as needed. Some clean spiderwebs can be used over the rags and under the tape, as an extra anti-bacterial layer if you choose.
Keep the person resting, and apply antibiotic ointment if you have it periodically. Check the area furthest away from the heart for each limb that has a bandage on it: check fingers for arm wounds and toes for leg wounds. If a bandage is too tight, it may cut off blood flow to the area below it, and you will need to loosen it immediately.