Final answer:
When sizing an uncuffed ET tube for a child, you can use either the age-based formula or the weight-based formula. The age-based formula uses the child's age to determine the tube size, while the weight-based formula uses the child's weight in kilograms.
Step-by-step explanation:
When sizing an uncuffed endotracheal (ET) tube for a child, you take into consideration the child's age, height, and weight. One commonly used formula for sizing is the age-based formula, which suggests using a 4 + age/4. For example, if a child is 8 years old, the tube size would be 4 + 8/4 = 6. Another method is using the weight-based formula, which suggests using the child's weight in kilograms to determine the tube size. For instance, if a child weighs 20 kilograms, the tube size would be around 3.5.