A child can have pain and not show it. Some pains that are short and sharp, like needle pain, cause more change in behavior. Pain that lasts longer than a few hours may cause few changes in behavior. A child's behavior can change for reasons other than pain. Sometimes, children cannot talk about their pain.
Parents are likely to be the best judge of what changes in behavior suggest pain.
How the child's body is reacting Heart rate, blood pressure, skin sweating and the amount of oxygen or carbon dioxide in the blood change in response to short sharp pain. However, these changes usually don't last long. These biological measures can also change because of anxiety, hunger or because of some medical condition. Measurement of pain in babies, especially sick babies, is perhaps the most difficult of all. Changes in heart rate, changes in the amount of oxygen in the blood and changes in facial expressions are the most widely used.