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Paediatric Weight Estimation: Small change – Big Difference?

Paediatric Weight Estimation: Small change – Big Difference?. Dr Mark Luscombe Consultant Anaesthetics/Critical Care Doncaster Royal Infirmary. Today’s Talk. Aim to look at two questions: Does the current APLS weight estimation formula remain valid? Is there a better alternative?.

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Paediatric Weight Estimation: Small change – Big Difference?

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  1. Paediatric Weight Estimation: Small change – Big Difference? Dr Mark Luscombe Consultant Anaesthetics/Critical Care Doncaster Royal Infirmary

  2. Today’s Talk • Aim to look at two questions: • Does the current APLS weight estimation formula remain valid? • Is there a better alternative?

  3. Increasing Weight • Concern over obesity in children • Is it just extremes or are children in general heavier? • Is there a real weight change or just a perceived change?

  4. North & South Magazine

  5. Medical Literature

  6. Population Characteristics

  7. Pilot Studies • First Study in Whangarei Hospital NZ (n=103) • Predicted weight is = 2(Age+4) • Children aged between 1 and 10 yo • Acute or day-case surgery in a 3 month period • Compared recorded weights with predicted weight

  8. Results • 90% children greater than estimated weights • NZ mean weight difference = 24.75% (95% CI = +19.25% to +30.25%)

  9. Pilot Studies • Second Study in Doncaster Royal Infirmary UK (n=134) • Method and Inclusion criteria as previous study

  10. Results • 86%(UK) children greater than estimated weights • UK mean Weight Difference = +18.46% • 95% CI = +14.87% to +22.05% • Compared with NZ +24.75%

  11. Problems & Solutions • Current estimation formula significantly underestimates weight • More accurate formula required •  Use Data to derive new formula

  12. Importance of Weight Estimation • Often needed for critically ill • Relied upon for: • Drug Dosages • Fluid Bolus (& Maintenance) • DC Shock settings • Ventilator settings • Urine output • Decision to ventilate based upon fluid given

  13. New Formula • Include 2 Standard deviations • Draw straight line of best fit • Result is: • Weight = 2.37 x Age + 9.63 (NZ) Weight = 2.52 x Age + 7.56 (UK)

  14. New Formula - Criteria • 1) Simple to use • 2) More accurate than previous • 3) In general should avoid over-estimation of weight • Two Options considered • Weight = 2 x (Age + 5) and • Weight = 2.5x (Age + 4)

  15. Early Conclusions • Children are heavier than predicted by current formula • The current formula is a poor estimate of the modern child’s weight. • Both new formulae tried were more accurate

  16. Pilot studies recommendation - Which New Formula? • Weight = 2x(age+5) • Whilst not as accurate on average asthe other formula tried, it is: • 1) More accurate than Weight = 2x(age+4) • 2) Likely to avoid drug over-dosage • 3) Simple to calculate

  17. Publication • Luscombe M D, “Kids aren’t like what they used to be”: a study of paediatric patient’s weights and their relationship to current weight estimation formulae. British Journal of Anaesthesia 2005; 95(4): 578

  18. Next Step • Larger scale study – need minimum n=400 • Checklist • Proposal • Protocol • Co-researchers • Ethical Approval • Finance Form • Research and development approval at research centre • Collect data and analyse • Statistician • Write it! • Publish

  19. Next Step • Luscombe MD & Owens BD • Data from Queens Medical centre, Nottingham UK, ED database • 6 months data n= 17244 test sets of data. • Age/Weight/Ethnicity/A&E Category

  20. Differences from pilot studies • Many more formulae tested • Check made on weights by A&E category. • Individual ages considered • Graphical representation • Ethnicity considered • Formulae tried : Weight = • 2age+9 • 2age+11 • 2(age+5) • 2(age+6) • 2.5(age+3) • 2.5(age+4) • 3(age+2) • 3(age+3) • 3age+7 • 3age+8

  21. Necessary? • Weights of Category 1 patients (Acute-Life Threatening) recorded = 41.5% • Weights of Category 5 patients (Minor injury to Emergency Nurse Practitioner) = 94.1% • Overall weight recording = 81.7%

  22. Necessary? • Weight estimate is still needed • Previous reasons for accurate weight assessment remain valid i.e. • Drug Dosages • Fluid Bolus (& Maintenance) • DC Shock settings • Ventilator settings • Urine output • Decision to ventilate based upon fluid given • Weight estimate may persist into ICU stay

  23. Additional Information • No evidence base for Weight=2(age+4) found • Fanconi, Wallgren & Collis “Textbook of Paediatrics” 1952 – Weights listed for age groups • Small “audit” type projects had also found more accurate formulae.

  24. Results • All formulae tried were more accurate overall • 3 formulae matching criteria • Weight = 3(age)+7 • Weight = 2.5(age+3) • Weight = 2(age+5) • Weight = 2(age+4) remains poor estimate

  25. Graphical Representation

  26. Which Formula? • Weight = 3(age) + 7 • Mean Weight Difference = 2.48% (95%CI = 2.17% to 2.79%) • Same at age 1 then more accurate at all other ages than current formula. • It is more accurate than all the other formulae from age 6 and older. • Mean weight difference 2(age+4)= 18.8% • (95% CI = 18.42% to 19.18%).

  27. Dissemination • Luscombe MD & Owens BD. Weight estimation in resuscitation: is the current formula still valid? Archives of Disease in Childhood 2007;92:412-415 • Numerous presentations

  28. Any problems? • Formula is an estimate • Overestimate in 4-5-6yrs old group • Only from 1 – 10yrs old • Ethnicity not recorded • Data from one area and in the UK only

  29. Further WorkSheffield Children’s Hospital Validation StudyLuscombe MD, Owens BD, Burke D.Ages up to 16yrsSheffield n= 41792Interim Results:

  30. Further work

  31. Interim Conclusions • Results validate previous study in new population • Weight = 3(age)+7 more accurate 1-10yrs • Weight = 3(age)+7 more accurate 1-16yrs • “Acceptable” accuracy 1-12yrs • Puberty • Males approx 11.5yrs • Females approx 10.5yrs • Formula works from 1 yrs to puberty

  32. Thank you • To ALSG for inviting me. • For your interest. • To Ben Owens and the many who have helped.

  33. Any Questions? • References • Fanconi G, Wallgren A, Collis WRF. Textbook of Paediatrics. William Heinemann Medical Books Ltd, London 1952 • Luscombe M D, “Kids aren’t like what they used to be”: a study of paediatric patient’s weights and their relationship to current weight estimation formulae. British Journal of Anaesthesia 2005; 95(4): 578 • Luscombe MD & Owens BD. Weight estimation in resuscitation: is the current formula still valid? Archives of Disease in Childhood 2007;92:412-415 • A M Fredriks, S van Buuren, et al, Arch Dis Child 2000;82:107–112 • Jain, A Fighting Obesity, BMJ 2004;328;1327-1328 • The advanced life support group, Advanced Paediatric Life Support, Fourth Edition, BMJ Publishing Group 2004 • The Dominion Post NZ December 2004 • North & South Magazine NZ May 2004 Weight = 3(age) + 7

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