What blood pressure ranges should be used when attempting to diagnose shock in children?

Because shock in the pediatric population is more often caused by hypovolemia than any other cause, patient history can be an immediate “heads-up.” There are reproducible changes that take place as perfusion failure progresses. These are: 

• Tachypnea: The pulmonary response to reduced tissue oxygen delivery is increasing the minute ventilation. This is done in large part through increasing respiratory frequency. Compensatory tachypnea is typically easy to differentiate from a pulmonary cause because of the history and a lack of signs of increased work of breathing.
• Tachycardia: The basic cardiac response to decreases in ventricular filling pressure is an increase in cardiac rate. This may pose an issue in differentiation of the mechanism of certain narrow QRS tachycardias. Progressing signs of perfusion failure with an increasing heart rate usually rules out arrhythmia and identifies compensatory sinus tachycardia.

Vasopressor response, or reflex vascular constriction, is seen in pediatric patients with worsening hypovolemia. This response may keep measured arterial blood pressure numbers in a “normal range” while the patient is approaching life-threatening shock. Hence, measurement of arterial blood pressure is not a recommended tool in the diagnosis of early shock in children. 

Rather, measurement of capillary refill avoids the compensatory masking. Squeezing blood from a large finger or small foot, then releasing the pressure allows of the observation of blood refilling the tissue. In a child with normal perfusion who is not hypothermic, this should take one to two seconds.