How much blood can you lose?

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If you've ever been unlucky enough to attend the scene of a serious accident, you'll have been shocked to see just how quickly an injured person can lose large amounts of blood. There's no telling what injuries a person might sustain in an accident, from minor cuts and bruises to the severing or crushing of limbs and exposure of arteries. In the latter scenario, it's essential that the emergency services arrive on the scene as quickly as possible to control blood loss which if left untreated can reach a critical state within minutes.

What is blood and how much can we lose?

Blood is the essential fluid that delivers oxygen throughout the body to organs, tissues and cells. Composed of 55% viscous liquid known as plasma, the remainder is made up of 45% cells and platelets. Red blood cells only live for about 120 days before they break down and become reabsorbed and replaced by new ones produced from within our bone marrow. Our blood supply is therefore constantly renewed and the body is quick to compensate any losses too, with the help of certain foods particularly those rich in iron, vitamin B12 and folate, such as spinach, lentils and avocados. Adult human beings have at least eight pints, or five litres, of blood in their circulatory system at any one time, however, blood volume varies according to body size and fitness levels and people with larger frames could have around 10 or maybe even up
to 12 pints. Altitude is another factor, with people living at high altitudes, in the Andes for example, having substantially more blood cells than the average person.

A healthy person could lose up to 15% of the blood in his body without experiencing any ill effects, a minor trauma known medically as class 1 hemorrhage. If loss of blood reaches up to 30%, signifying Class 2 hemorrhage, the patient will experience a rapid heart beat and blood pressure will be adversely affected. Blood vessels become narrow as their muscular walls contract, meaning that less blood reaches the surface of the skin. The patient therefore becomes pale and cold and will certainly feel and act disorientated. Although it is not necessary to administer a blood transfusion, the patient will require an intravenous drip of saline solution; the safest type of fluid that can be given in large quantities. Hitting the category of Class 3 hemorrhage involves the loss of 30-40% of blood supply which leads to severe disorientation, further
taquicardia and a sharp drop in blood pressure. The patient is likely to pass out, risk entering a state of circulatory shock and will almost certainly need a blood transfusion as well as a drip. Any loss of over 40% of total blood supply is categorised as class 4 hemorrhage or desanguination. Anyone suffering such a critical trauma will require immediate attention and resuscitation to avert death. Complete loss of blood from the body would be known as exsanguination and would cause certain death.

The reason why we can easily become disorientated or pass out during episodes of substantial blood loss is because the brain relies on around 20% of our entire blood supply and a quarter of the oxygen it distributes in order to function correctly. This equates to around 740 millitres of blood circulating through every 100 grams of brain tissue each minute, delivering 3.3 millilitres of oxygen to the cells that rely on it to stay alive and function normally.

Of course, there are certain types of people who are either more or less prone to the adverse effects of bleeding. The elderly for instance would be in particular danger after losing a large amount of blood, whereas very fit young people with healthy cardiovascular systems would be less susceptible and more able to survive a trauma.

Types of blood loss

Bleeding can occur externally, either through an existing orifice such as the nose or a superficial wound such as an incision in the skin, or internally, when blood escapes from internal organs. Light external bleeding does not usually indicate an urgent problem unless the patient suffers from a rare condition known as haemophilia, in which the blood will fail to clot normally. Applying pressure to a superficial wound using a bandage will normally be sufficient to stop the blood flow. Loss of blood from an orifice can sometimes be a result of internal bleeding, which is usually indicative of a serious problem. Bleeding from the rectum for example could be indicative of a tumour in the bowel or more commonly, hemorroids, whereas bleeding from the nose is fairly common and rarely serious, usually a result of the rupture of capillaries in the nasal passages.

Giving blood

In the UK the National Blood Service is responsible for actively encouraging and collecting regular donations of blood from the public to allow our hospitals to carry out essential life saving operations and procedures. A colossal 7,000 blood donations are needed every single day and although the public responds favourably, donating 2.1 million units a year, this equates to just around 4% of the total population who are registered donors giving blood just 3 times a year. Blood donation is safe and painless and takes place at blood centres and mobile donating units throughout the country. Blood donation will only take around 8-10% of a person's blood supply which as we have illustrated, will not cause any adverse effects on the body. As freshly donated blood only has a lifespan of 5 weeks, it's essential that supplies are constantly updated, hence the pleas from the National Blood Service to us all to 'do something amazing' and give blood.

How much blood can you lose?

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What is blood and how much can we lose?

Types of blood loss

Giving blood

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