Weight Estimation Formula Beats Argall, APLS

September 2010

By M. Alexander Otto
Elsevier Global Medical News

PHOENIX - A new pediatric weight estimation method--the Luscombe formula--is more accurate than the Argall and Advanced Pediatric Life Support formulas, as well as the best-guess method, according to a recent study.

It was the first validation study of the Luscombe formula, which was proposed in 2007, according to Dr. Barry Gunn, an emergency physician at Sunshine Hospital in Melbourne.

The Luscombe formula is as follows: Multiply the age of the child by 3, then add 7. The resulting weights are given in kilograms, and the method is applicable to children aged 1-10 years.

When it's not possible to weigh a child, parental estimation and the Broselow tape still remain the best options, Dr. Gunn said at the annual meeting of the Society for Academic Emergency Medicine.

But when parents aren't available, and the child is too tall for the Broselow tape or the tape isn't at hand, the Luscombe formula is the next best option, based on the study's findings.

Dr. Gunn and his colleagues compared the actual weights of 410 children presenting at his emergency department against Luscombe, Argall, Advanced Pediatric Life Support (APLS), and best-guess estimations. Median age was 4 years; 54% were boys, and 75% were white.

The Luscombe method is not perfect: Just 45% of its estimates were within 10% of measured weight, with a mean difference of 0.66 kg from actual weight. Accuracy deteriorated at higher measured weight, especially for children older than 5 years. However, the formula still outperformed the other methods.

Best guess was a close second to Luscombe estimation, with 42% of guesses within 10% of actual weight and a mean difference from actual weight of 0.7 kg.

Just 37% of Argall estimates were within 10% of actual weight, with a mean difference from actual weight of 1.7 kg; 34% of APLS estimates were within 10% of actual weight, with a mean difference of 4.3 kg.

Dr. Gunn said the Luscombe formula is the go-to formula in his ED for drug dosing, fluid volumes, and calculating defibrillation electricity doses.

Changing age-weight relationships could be why the older APLS and Argall formulas are no longer acceptably accurate. The populations in which they were developed may also have been relatively underweight, he said.

The original study of the Luscombe formula found it to be accurate in a retrospective study of 17,244 children aged 1-10 years, with a mean underestimation of 2.48% (Arch. Dis. Child. 2007;92:412-5).

Dr. Gunn said he has no disclosures. The study had no outside funding.

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