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Knowing a child's age is important to determine normal vital signs, disease prevalence, and the appropriate medications. It is also an indicator of social milestones. The easiest way to determine a child's age is to ask the parent or check available records. However, in cultures where birth records are unavailable, as well as during acute out-of-hospital or emergency department (ED) events, this information may not be easy to get.
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Without records, one way to estimate a child's approximate age is to count the number of teeth present and then add six to derive the age in months.1 Another way is to have the child sit upright (with the head in a neutral position), then raise one arm over his head and try to touch the opposite ear (Fig. 7-1). This "overhead test" has a sensitivity of 90% and a specificity of 78% (positive predictive value 93%; negative predictive value 68%). If the child successfully performs this test, he is most likely ≥6 years old, which is the age to begin school and to receive other benefits in many cultures. If a child fails this test, there is a good chance that he is <6 years old, but it is less clear, since other factors, such as malnutrition, may influence the results. The test works because a 6-year-old child's humerus is long enough to raise the elbow high enough to extend the forearm across the head and allow the fingers to reach the opposite side of the head.2
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Any firm surface can be marked in 0.5-cm (or 0.5-inch) increments to measure a patient's height. For ambulatory patients, use a vertical surface, such as a wall or the side of a doorway. For infants, children, and bed-ridden patients, mark the side rails of stretchers and beds with indelible ink. Once a child's height is known, the weight can be estimated.
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Using a stretcher marked along the side to measure a child's height is extremely useful; knowing the child's height, you can estimate weight, and this provides the information necessary to calculate pediatric medication and fluid dosages.
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If an adult's height can be measured only in a sitting position, such as a wheelchair-dependent patient, measure each arm span in centimeters, from mid-sternum to the end of the extended middle finger (half-arm span). Use the longer of these measurements in the following formula: Height ≅ (0.73 × [2 × half-arm span]) + 43 cm.3 A simpler method is to double the longest measurement from mid-sternum to the tip of the patient's long finger.4
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Need to estimate a child's weight? When asked, the parents of children aged from 1 to 11 years old can estimate their child's weight ...