Ask Bizarre - Blood loss
April: How much blood does a person have to lose generally before the blood loss becomes fatal? Does the position of the body have anything to do with the speed of their death, i.e, would a person on their back die quicker than a person propped upright?
DR MIKE: Maximum allowable blood loss (MABL) is calculated using a formula which takes into account body weight, your body composition (the number of millilitres of blood per kg of body weight) and your haemoglobin (Hb) count — that’s a measure of the oxygen-carrying capacity of your blood. You’d need a blood test to measure your Hb count, but if you assume it’s in the typical range of 14-18 g/dL (for men) or 12-16 g/dL (for women), and that your body composition is also average (it’s usually about 72ml/kg) then the appropriate formula — MABL = (Hb - minimum Hb)/Hbjx x body composition — is easy to calculate.
The formula reveals that a 70kg adult has a MABL of 1440ml, which is the same as saying an 11 stone adult is in serious trouble if they lose more than 2.5 pints of blood. A 25-stone chubby behemoth, on the other hand, could lose almost 6 pints of blood and still survive.
And, of course, anything which speeds up blood loss will also speed death, so it would certainly help to position yourself with your wound facing upwards and to staunch the flow of blood with bandages or a cloth if possible.