Shock is the inadequate perfusion (blood flow) to vital organs.

In trauma patients, it is most commonly caused by blood loss.

Table 1 describes the classical signs of shock. However, patients do not all follow the textbooks!

30% of the circulating blood volume or 1500ml can be lost before the blood pressure begins to fall! Young people compensate well, then deteriorate quickly.

	Class I	Class II	Class III	Class IV
Blood loss (%)	<15	15-30	30-40	>40
Blood loss (ml)	750	800-1500	1500-2000	>2000
Systolic blood pressure	Unchanged	Normal	Reduced	Very low
Diastolic blood pressure	Unchanged	Raised	Reduced	Unrecordable
Pulse (beats/minute)	Slight tachycardia	100-120	120 (thready)	>120 very thready
Capillary refill	Normal	Slow (>2 seconds)	Slow (>2 seconds)	Undetectable
Respiratory rate	Normal	Tachypnoea	Tachypnoea >20/minute	Tachypnoea >20/minute
Urine output	>30	20-30	10-20	0-10
Extremities	Normal	Pale	Pale	Pale, cold and clammy
Complexion	Normal	Pale	Pale	Ashen
Mental state	Alert	Anxious or agressive	Anxious, agressive or drowsy	Drowsy, confused or unconscious

Table 1 Classes of shock