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BMJ Innovations Publish Ahead of Print, published on May 21, 2015 as doi:10.1136/bmjinnov-2015-000059
ASSISTIVE TECHNOLOGIES
ORIGINAL ARTICLE
A novel tool to aid usability of agebased weight estimation formulae
Dilshad Marikar
Correspondence to
Dr Dilshad Marikar, Department
of Paediatrics, Bedford Hospital
NHS Trust, Kempston Road,
Bedford MK42 1DJ, UK;
[email protected]
Received 19 April 2015
Accepted 24 April 2015
ABSTRACT
Age-based weight estimation methods are used
in the resuscitation of children deemed too sick
to weigh. Some methods involve multiple
formulae, which can be difficult to recall and
use. This paper presents a conceptually simple
finger-counting method that can be used to
rapidly estimate weight based on existing
age-based formulae.
INTRODUCTION
Age-based weight estimation formulae are
used in paediatric patients deemed too
sick to weigh. Since 2011, the Advanced
Paediatric Life Support (APLS) course has
suggested three formulae for weight estimation: (age×0.5)+4 for children aged
1–12 months, (2×age)+8 for children
aged 1–5 years and (3×age)+7 for children aged 6–12 years.1 There is evidence
to suggest multiple formulae are time
consuming2 as well as being difficult to
recall; a survey of a group of paediatric
trainees found that 92% were unable to
recall the latest APLS formulae.3
To address these issues, this paper
presents a conceptually simple fingercounting technique that can be used with
common age-based weight estimation formulae. Its application to APLS formulae
is demonstrated.
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METHOD
Place your hands in front of you, palms
up: counting from left to right, digits 1–5
on the left hand represent 1–5 years, and
digits 6–10 on the right hand represent
6–10 years.
The following two estimated weights
are memorised: 10 kg for a 1-year-old
child and 25 kg for a 6-year-old child
(figure 1). To estimate weight for children
aged 1–5 years, start with the memorised
weight for 1 year (10 kg) and count the
fingers on the left hand up to the desired
age, adding 2 kg for each finger, To estimate weight for a child aged 6–10 years,
start with the memorised weight for a
child of 6 years (25 kg) and count the
fingers on the right hand up to the
desired age, adding 3 kg for each finger.
To estimate weight for infants aged
1–10 months (figure 2), from left to right
the operator’s digits represent the ages
1–10 months. The estimated weight for a
child of 1 month is memorised (4.5 kg).
Weight for age is estimated by counting
fingers up to the desired age from left to
right, adding ½ kg for each finger.
An accompanying video tutorial for
finger counting with APLS4 is available
https://vimeo.com/89796060.
DISCUSSION
Although a validated finger counting
technique already exists with an aim to
aid usability of age-based paediatric
weight estimation,5 it does not map to
any existing weight estimation formulae
used in current practice. This method can
be applied to any linear age-based weight
estimation method formula—which will
be of use for researchers who wish to
develop new age-based formulae, validated for the population in which they
work. Further tutorial videos have been
produced to illustrate its use in this
regard.6
It is important for clinicians to note
that any age-based weight estimation formulae will have limited precision,7 and
the latest APLS weight estimation formulae are no exception.8 Readers may be
also struck by a marked 7 kg jump in estimated weight from 5 to 6 years as a
result of using two different formulae
(figure 1). This is a result of a decision by
the APLS working group to split two formulae between the ages 1–12 years,
based on comparison of accuracy of an
Marikar D. BMJ Innov 2015;0:1–3. doi:10.1136/bmjinnov-2015-000059
Copyright 2015 by All India Institute of Medical Sciences.
1
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ASSISTIVE TECHNOLOGIES
Figure 1 Advanced Paediatric Life Support (APLS) finger counting method for children aged 1–10 years (background image
courtesy of Evan Amos, freely licensed via Creative Commons).
Figure 2 Advanced Paediatric Life Support (APLS) finger counting method for children aged 1–10 months (background image
courtesy of Evan Amos, freely licensed via Creative Commons).
earlier APLS formula and the newer Luscombe et al9
equation against UK-WHO 50th centile growth chart
data ( personal communication via Jane Mooney,
APLS working group, August 2013).
I suggest this technique may act as a complementary
resuscitation aid to help reduce the cognitive load
associated with paediatric emergencies10—especially
in situations where age-based formulae, computerised
methods or precalculated tables of estimated weight
are not immediately at hand.
Twitter Follow Dilshad Marikar at @MDMarikar
Acknowledgements DM would like to thank C Hills for
producing the tutorial video for this concept.
Contributors DM developed the concept and produced the first
draft of this manuscript.
2
Competing interests None declared.
Provenance and peer review Not commissioned; internally peer
reviewed.
REFERENCES
1 Advanced Life Support Group. Advanced paediatric life
support. Wiley-Blackwell, 2011.
2 Marlow RD, Wood D, Lyttle LD. Comparing usability of
paediatric weight estimation methods [abstract]. Arch Dis Child
2013;98(Suppl 1):A107–8.
3 Marikar D, Varshneya K, Wahid A, et al. Just too many things
to remember? A survey of paediatric trainees’ recall of
Advanced Paediatric Life Support (APLS) weight estimation
formulae. Arch Dis Child 2013;98:921.
4 Marikar D, Hills C. APLS 2010 Weight Estimation. http://
vimeo.com/89796060 (accessed 4 Jul 2014).
Marikar D. BMJ Innov 2015;0:1–3. doi:10.1136/bmjinnov-2015-000059
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ASSISTIVE TECHNOLOGIES
5 Young TP, Chem BG, Kim TY, et al. Finger counting: an
alternative method for estimating pediatric weights. Am J
Emerg Med 2014;32:243–7.
6 Marikar D, Hills C. Weight Estimation Videos. http://vimeo.
com/user26138620/videos (accessed 4 Jul 2014).
7 Cattermole GN, Graham CA, Rainer TH. Paediatric weight
estimation. Emerg Med J 2012;29:82–3.
8 Carley S. APLS weight estimation—don’t do it (well almost
never). Weblog. http://stemlynsblog.org/apls-estimation-
Marikar D. BMJ Innov 2015;0:1–3. doi:10.1136/bmjinnov-2015-000059
formulas-do-not-safely-predict-weight-in-uk-children-st-emlyns/
(accessed 13 Jun 2014).
9 Luscombe MD, Owens BD, Burke D. Weight estimation in
paediatrics: a comparison of the APLS formula and the formula
‘Weight=3(age)+7’. Emerg Med J 2011;28:590–3.
10 Luten R, Wears RL, Broselow J, et al. Managing the
unique size-related issues of pediatric resuscitation: reducing
cognitive load with resuscitation aids. Acad Emerg Med
2002;9:840–7.
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Downloaded from http://innovations.bmj.com/ on July 6, 2015 - Published by group.bmj.com
A novel tool to aid usability of age-based
weight estimation formulae
Dilshad Marikar
BMJ Innov published online May 21, 2015
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