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Neonatal urine output measurement by weighing nappies

Presented at the Neonatal Society 2007 Summer Meeting (programme).

Maddock N, Gottstein R

Neonatal Medical Unit, St Mary’s Hospital, Whitworth Park, Manchester M13 0JH,UK

Aim: To study the accuracy of using nappy weight change from dry as a measure of the amount of water added to a nappy in an incubator with standard air temperature and humidity settings. Assessing nappy weight changes from dry is frequently performed as a measure of urine output to determine fluid balance in sick, premature neonates (1-5).

Methods: Two types of disposable nappies Pampers Micro (suitable for infants weighing 1.5 - 3kg) and Pampers Premium (suitable for infants weighing 0.5 - 2.3kg) were examined. Two different air temperature settings (36.7ºC and 37.7ºC) and 70% humidity was used in an Atom Incubator – V-2100G1. Nappies were placed in an incubator with 0, 5, 10 or 15 mls of water added and left either open or around a plastic doll (Resusci®Baby). They were weighed at 1 - 2 hourly intervals to a maximum of 12 hours. This procedure was then repeated with the addition of phototherapy (Dräger Phototherapy 4000). All nappies were weighed using an EKS Electronic Scales.

Results: Both types of nappies to which no water had been added gained a maximum of 2g over the 12 hour study period at either air temperature settings. Percentage weight loss of added fluid was least when the nappies were closed around the plastic doll (0-10% weight loss at 4 hour, 20% at 6 hours and 30% at 12 hours versus 20%, 30% and 33.3% weight losses at 4,6 and 12 hours respectively when the nappy is open). No increase in percentage weight loss was seen with the addition of phototherapy (maximum percentage weight loss 20% at 4 and 6 hour and 40% at 12 hours).

Conclusion: Pampers Premium (smaller) nappies when closed around the plastic doll lost least amount of the added water and therefore are most accurate measure of urine output. Measuring nappy weights 6 hourly results in only a clinically insignificant weight loss. Even when leaving the nappy exposed to phototherapy there is a maximum weight loss of only 20% if weighed 6 hourly.

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2. Cooke, RJ, Werkman, S, Watson, D. Pediatrics 1989; 83: 116-118.
3. Hermansen, MC and Barnhart, MC. J Perinatology 1992; 12: 72-73.
4. Hermansen, MC and Buches, M. Pediatrics 1987: 79; 1056-7.
5. Oddie, S, Adappa, R and Wyllie, J. Arch Dis Child Fetal Neonatal Ed 2004; 89:F180-F181.

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