Apr 16, 2020 
When you lose more than a fifth of your blood, your blood pressure crashes and your heart struggles to pump a sufficient amount to your internal organs. This leads to a condition called hypovolemic shock, and ultimately to death if left untreated.
Serious blood loss is always a medical emergency. But there are three different types of bleeding, and they all signify different things. They include:
Arterial bleeding
The arteries carry oxygenated blood away from the heart and toward the internal organs—while veins carry oxygen-depleted blood back to the heart. This type of bleeding happens when there is a wound to a major artery.
Blood pressure inside the arteries tends to be higher than that in the veins—and when a major artery is injured, that’s demonstrated in dramatic fashion. Arterial bleeding is characterized by pulsing spurts, sometimes several meters high.
The blood in this kind of bleeding event is sometimes said to be bright red, because it’s oxygenated. However, the color of the blood can sometimes be difficult to discern.
Because of the fast spurts, arterial bleeding is often the most difficult to control. To treat it, apply direct pressure. If possible, ask the patient to hold a thick pad or dressing in place while you secure it with roller gauze. Don’t lift the dressing to see if the bleeding has stopped—instead, lift your hand to see if blood is seeping through.
Venous bleeding
Veins carry deoxygenated blood back to the heart. The blood pressure in your veins is lower than that in your arteries; because of this, if you injure a major vein, the wound may ooze rather than spurting.
Sometimes this blood is also noted to be darker in color than that of an arterial bleed—but again, this can be difficult to judge.
While venous bleeding is not as fast and dramatic as arterial bleeding, it is just as serious. As with arterial bleeding, the way to treat it is to apply direct pressure.
Capillary bleeding
This is bleeding of the tiny capillaries that exist close to the surface of the skin, as well as inside organs such as your lungs.
Capillary bleeding is usually superficial. You may see a fast flow of blood at first, but it usually slows to a trickle and is easily managed.
Often, capillary bleeding will stop on its own. If needed, applying a Band-Aid or other bandage can help stop it—just be careful not to get the sticky part of the Band-Aid on the cut.
Capillary bleeding may not be a big deal, but heavier bleeding is always a medical emergency—and you should always call emergency services as soon as the bleeding is controlled.