Final answer:
In ALS, pediatric weight is calculated using standardized growth charts or by actual measurement when possible, while BMI is not a reliable measure for children and adolescents due to their growth.
Step-by-step explanation:
The Advanced Life Support (ALS) system calculates pediatric weight in a medical emergency primarily through two methods: using standardized growth charts or by actual measurement on scene. Visual estimation or using Body Mass Index (BMI) is less reliable for pediatrics due to their ongoing growth and development. BMI in particular is not recommended for evaluating children and adolescents for this reason, and while a new BMI formula for these age groups has been introduced, it is not widely adopted. For a precise assessment, ALS providers often use standardized growth charts which correlate a child's height and age with expected weight ranges. These charts, like the WHO Child Growth Standards, provide reference points for boys and girls at different ages and lengths, which is particularly useful for children up to 3 years old.
Consider a scenario where an 80 cm tall girl in the reference population has a mean weight (μ) of 10.2 kg and a standard deviation (σ) of 0.8 kg. To calculate the z-score for a weight of 11 kg, subtract the mean (μ) from the weight and then divide by the standard deviation (σ): (11 - 10.2) / 0.8 = 1. This z-score means the weight is 1 standard deviation above the mean. For a weight of 7.9 kg, the z-score would be (7.9 - 10.2) / 0.8 = -2.875, indicating the weight is approximately 2.875 standard deviations below the mean.