What is the most likely early sign of hypoxia in a child?

Tachycardia is an early and common physiological response to hypoxia in children. When the body experiences low oxygen levels, the heart compensates by increasing the heart rate to maintain adequate blood flow and improve oxygen delivery to vital organs and tissues. In children, this response can be particularly pronounced because their cardiovascular systems are responsive to changes in oxygenation.

While mottled skin can occur in more severe cases of hypoxia or other critical conditions, it is typically not an early sign. Bradycardia may occur later in the progression of hypoxia, as the body becomes increasingly stressed or in a state of decompensation. Bradypnea may indicate a severe respiratory distress or failure, but again would not be an early sign. In summary, tachycardia effectively signals the body's attempt to adapt to hypoxia, making it the most likely early sign in a child.