Table 2.

American College of Surgeons Advanced Trauma Life Support (ATLS) classification of blood loss based on initial patient presentation. Signs and symptoms of haemorrhage by class

Parameter	Class I	Class II (mild)	Class III (moderate)	Class IV (severe)
Approximate blood loss	< 15%	15–30%	31–40%	> 40%
Heart rate	↔	↔/↑	↑	↑/↑↑
Blood pressure	↔	↔	↔/↓	↓
Pulse pressure	↔	↓	↓	↓
Respiratory rate	↔	↔	↔/↑	↑
Urine output	↔	↔	↓	↓↓
Glasgow coma scale score	↔	↔	↓	↓
Base deficit*	0 to − 2 mEq/L	− 2 to − 6 mEq/L	− 6 to − 10 mEq/L	− 10 mEq/L or less
Need for blood products	Monitor	Possible	Yes	Massive transfusion protocol

Table reprinted with permission from the American College of Surgeons [53]

Original data from Mutschler et al. [54]

*Base excess is the quantity of base (HCO₃⁻, in mEq/L) that is above or below the normal range in the body. A negative number is called a base deficit and indicates metabolic acidosis