• Mark Luscombe and Ben Owens.
• The Royal Hallamshire Hospital, Sheffield, South Yorkshire, UK. markluscombe@doctors.org.uk
• Arch. Dis. Child. 2007 May 1;92(5):412-5.

ObjectivesTo gather data on the ages and weights of paediatric patients between 1 and 10 years of age, and to compare these data with the current weight estimation formula weight(kg) = 2(age+4). If a significant difference was found, the data would be used to derive a more accurate formula.DesignRetrospective study using data collected from paediatric attendances at an emergency department (ED).SettingA large ED in a major UK city, treating both children and adults.Patients17 244 children aged 1-10 years, attending the ED between June and December 2005.Main Outcome MeasuresWeight difference between the measured weight and the expected weight, the latter given by weight = 2(age+4).ResultsThe weights of seriously ill children were recorded in only 41.5% of cases, necessitating a weight estimate in the remainder. The formula weight = 2(age+4) underestimated children's weights by a mean of 18.8% (95% confidence interval (95% CI) 18.42% to 19.18%). Using linear regression and analysis of each individual age group, ten new formulas were tested. Of these formulas, weight(kg) = 3(age)+7 proved the most accurate with a mean underestimate of just 2.48% (95% CI 2.17% to 2.79%).ConclusionsWeight estimation remains of paramount importance in paediatric resuscitation. This study shows that the current estimation formula provides a significant underestimate of children's weights. When used to calculate drug and fluid dosages, this may lead to the under-resuscitation of a critically ill child. The formula weight(kg) = 3(age)+7 provided a safe and more accurate estimate of the weight of today's child.

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