The most important sign of shock is a delayed capillary filling time of more than 3 seconds. The capillary filling time is measured by pressing on the sole of the child’s foot or palm of the hand, then releasing the pressure and counting how many seconds it takes for the pale area to regain its pink colour. Pressing on the nail of the middle finger can also be used to measure the capillary filling time. In order to count in seconds, and not too fast or too slow, it is useful to count ‘one crocodile, two crocodiles, three crocodiles, etc’. The return of colour to the pale area is due to the capillaries filling once more with blood. Therefore, this is a good way of assessing the state of the peripheral circulation (the blood flow through the capillaries). Slow filling of the capillaries shows that the blood is not circulating properly.
A delay in the capillary filling time is the best way of diagnosing shock.