Clinical paperMid-arm circumference can be used to estimate children's weights☆
Introduction
In paediatric resuscitation, it is necessary to know the child's weight in order to provide appropriate drug and fluid doses, equipment selection and ventilator settings. Because measurement of weight itself is rarely possible in time-critical situations, and because there is often no one available who knows the child's weight, rapid and accurate methods of estimation need to be applied. Most commonly, weight can be estimated from formulae based on the child's age,1 or from the child's height using the Broselow tape.2
Other suggested methods include weight estimation according to foot-length, or mid-arm circumference (MAC).3, 4, 5 Neither is currently used in clinical practice for weight estimation in paediatric resuscitation. However, a formula including MAC and knee height has recently been validated in geriatric patients in the emergency department.6 MAC has also been used for many years in the assessment of malnutrition in the developing world.7
One of the most widely used age-based estimation method is that recommended in the UK-based Advanced Paediatric Life Support course1: weight in kg = 2 × (age in years + 4). It has been criticised for under-estimating children's weight, and new formulae have been derived.8, 9 The Broselow tape has consistently been found to outperform age-based formulae in estimating weight,8, 10, 11 but both the Broselow tape and age-based weight estimation methods are less precise in older and heavier children.2, 8, 10, 12, 13 Systematic underestimation of childhood weight is likely to be due to the increasing actual weights, especially of older, Western children. The US National Health and Nutrition Examination survey has demonstrated a steady increase in childhood obesity: data from 1999 to 2002 found that 16% of 6–19 year olds, and 10.2% of 2–5 year olds, were overweight (≥95th centile body mass index).14 In 6–18 year olds in Hong Kong, the proportion increased from 7.1% to 10.1% between 1993 and 2006.15
It is not known whether a weight-estimation method based on foot-length or MAC might be more appropriate than either the Broselow tape or age-based methods, especially in older children.
The objectives of this study were to determine which of age, height, foot-length or MAC had the strongest relationship with weight in healthy children, to derive a simple weight-estimation formula from the strongest correlate, and to compare its performance with existing weight-estimation tools.
Section snippets
Methods
This was a population-based observational study, part of the prospective “Healthy Children's Vital Signs and USCOM study”, which also included physiological and ultrasound cardiac output monitor (USCOM) measurements. It was conducted in primary schools and kindergartens in Hong Kong, and recruited healthy Chinese children aged 1–11 years on their last birthday.
Head teachers of all relevant institutions in the Shatin area of Hong Kong were asked for permission to have their schools participate
Results
1391 Chinese subjects aged 1–11 years on their last birthday were recruited from 14 schools and kindergartens. In the six institutions which recorded how many consent letters were distributed, 48% of invited parents consented. The time constraints of school timetables prevented us from obtaining all four anthropometric measurements in 21 children, who were excluded from further analysis. 1370 (98.5% of the eligible sample) were therefore included, of whom 55% were boys. There were 448 children
Discussion
We have shown that MAC is the strongest correlate with children's weight, in all age-groups, and that this relationship strengthens with age. Height, foot-length and age are also correlated with weight, but this relationship weakens with age, and only height remains an important correlate in older children, alongside MAC. We have derived a weight-estimation formula based on mid-arm circumference: weight = (MAC − 10) × 3. This rule out-performs the Broselow tape and the APLS age-based formula in older
Conclusion
Weight correlates more strongly with mid-arm circumference in children, than with age, height or foot-length. We have derived a weight-estimation formula based on mid-arm circumference: weight = (MAC − 10) × 3. This rule out-performs the Broselow tape and the APLS age-based formula in older children, but is less suitable in children under 6 years old. A colour-coded arm-tape could be developed for rapid assessment of paediatric weight in the resuscitation room for use in older children.
Conflict of interest statement
None of the authors has any competing interests to declare.
Funding
We received a Direct Grant, ref. 4450252, of HK$72,000 (approximately US$10,000) from the Chinese University of Hong Kong to conduct the “Healthy Children's Vital Signs and USCOM Study”. We also received a grant of HK$100,000 (approximately US13,000$) from the Hong Kong College of Emergency Medicine.
References (30)
- et al.
A rapid method for estimating weight and resuscitation drug dosages from length in the pediatric age group
Ann Emerg Med
(1988) - et al.
A better way to estimate adult patients’ weights
Am J Emerg Med
(2009) - et al.
How reliable is length-based determination of body weight and tracheal tube size in the paediatric age group? The Broselow tape reconsidered
Br J Anaesth
(2002) - et al.
Measuring malnutrition
Lancet
(1974) - et al.
Calculation of drug dosage and body surface area in children
Br J Anaesth
(1997) - et al.
Towards better weight estimation in the seriously ill child—a comparison of methods
Arch Dis Child
(2001) Relationship of upper arm circumference and body weight
J Emerg Nurs
(1985)Mid-arm circumference: estimating patients’ weight
Dimens Crit Care Nurs
(1990)- et al.
Community nutritional assessment
(1989)
A comparison of two commonly used methods of weight estimation
Arch Dis Child
Weight estimation in resuscitation: is the current formula still valid?
Arch Dis Child
Are methods used to estimate weight in children accurate?
Emerg Med (Fremantle)
Parental weight estimation of their child's weight is more accurate than other weight estimation methods for determining children's weight in an emergency department?
Emerg Med J
Evaluation of the accuracy of different methods used to estimate weights in the pediatric population
Pediatrics
Cited by (0)
- ☆
A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2010.05.015.