Validation of a local weight estimation formula in children undergoing surgery at the University Teaching Hospital, Lusaka, Zambia

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Phiri, Hope
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University of Zambia
Accurate determination of weight is essential to avoid drug errors. Where weighing is not feasible, age or length based formulae are used to estimate weight. Formulae must be validated in the local population as most are derived from high income countries where childhood obesity is increasing. The “Lusaka formula” was derived from a previously published data set. The study aimed to validate this formula in a new data set. Weights, heights and age of 330 children were measured before surgery. Accuracy was examined by comparing the (1) Mean Percentage Error and (2) the percentage of actual weights that fell between 10% and 20% of the estimated weight for the Lusaka formula and other existing formulae. The Lusaka formula had a mean percentage error of 1.37% (95% limits of agreement 7.7,-6.8) and estimated weights to within 10% of actual weight 48.5% of the time. It had a slight tendency to underestimate weights. Its precision was comparable to the Broselow tape. No significant difference was found between the sexes with regards to the mean age, measured weight and estimated weights differences but regression analysis showed that maternal education level significantly predicts weight for children above 1 year. Out of the 163 children aged 0-5 years, 17.8% had under nutrition of varying extents; 3.1% had extreme malnutrition, 3.1% had severe malnutrition and 11.7% had moderate malnutrition. The study concluded that when actual weight is unknown, the Lusaka formula is superior to previously published age based weight estimating formulae in children presenting for surgery at the University Teaching Hospital (UTH) in Lusaka, Zambia. Newer formulae significantly overestimated weights of the children in this population. Keywords: Paediatric, weight estimation, low middle-income countries.
Surgery--children , Children--Health and hygiene--Zambia , Children--Anthropometry.