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 = %
(95% CI = % to %)

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 = %
95% CI = % to %
Compared with NZ %

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 (NZ) Weight = 2.52 x Age (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 as the 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= 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? Mean Weight Difference = 2.48%
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:
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 Work Sheffield Children’s Hospital Validation Study Luscombe MD, Owens BD, Burke D. Ages up to 16yrs Sheffield n= Interim Results:
Formula
Mean Weight Diff
1-10yrs
11-16yrs
Mean Weight Diff 11-12yrs
Mean Weight Diff (all)
2(age+4)
22.45%
59.43%
51.02%
34.14%
3(age) + 7
2.62%
17.93%
12.81%
7.45%

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:
A M Fredriks, S van Buuren, et al, Arch Dis Child 2000;82:107–112
Jain, A Fighting Obesity, BMJ 2004;328;
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