Weight estimation in paediatrics: a comparison of the APLS formula and the formula 'Weight=3(age)+7'.

OBJECTIVES

To gather data on the ages and weights of children aged between 1 and 16 years in order to assess the validity of the current weight estimation formula 'Weight(kg)=2(age+4)' and the newly derived formula 'Weight=3(age)+7'.

DESIGN

Retrospective study using data collected from paediatric attendances at an emergency department (ED).

SETTING

A large paediatric ED in a major UK city.

PATIENTS

93,827 children aged 1-16 years attending the ED between June 2003 and September 2008.

MAIN OUTCOME MEASURES

Percentage weight difference between the child's actual weight and the expected weight, the latter determined by 'Weight(kg)=2(age+4)' and by 'Weight(kg)=3(age)+7', in order to compare these two formulae.

RESULTS

The weights of seriously ill children were recorded in only 20.5% of cases, necessitating a weight estimate in the remainder. The formula 'Weight=2(age+4)' underestimated children's weights by a mean of 33.4% (95% CI 33.2% to 33.6%) over the age range 1-16 years whereas the formula 'Weight=3(age)+7' provided a mean underestimate of 6.9% (95% CI 6.8% to 7.1%). The formula 'Weight=3(age)+7' remains applicable from 1 to 13 years inclusive.

CONCLUSIONS

Weight estimation is 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=3(age)+7' can be used over a larger age range (from 1 year to puberty) and allows a safe and more accurate estimate of the weight of children today.