Downloaded from http://adc.bmj.com/ on June 14, 2017 - Published by group.bmj.com
246
Wyatt, Robertson, Scobie
puncture wounds. This inadequate protection
against hepatitis B may reflect the limited
experience of individual doctors: when expert
advice was obtained, protection against
hepatitis B was given in 36 of 37 (97%) cases.
Similarly, the possibility of tetanus appears to
have been neglected in many children.
Although no child is known to have subsequently developed any sequelae, follow up
was inadequate. The possibility of testing
material within a needle brought with a child to
hospital and saving the child's serum (to help
identify the time of any seroconversion) should
be considered.
Attempts to prevent HIV seroconversion
remain of unproved value.6 Attention should
be directed towards the prevention of needlestick injuries. This might be achieved by
publicising the dangers of needles and by
urging drug abusers to dispose of needles in a
more responsible manner. Perhaps children
living in 'high risk' areas should be offered
routine prophylaxis against hepatitis B at a
young age.
We recommend that a plan should be available in accident and emergency departments
for managing out of hospital needlestick
injuries. This plan would include prophylaxis
against hepatitis B and tetanus and allow
referral to an appropriate expert for counselling and follow up.
We thank Dr Mok and Dr Peutherer for their help.
1 Peutherer JF, Edmond E, Simmonds P, Dickson JD, Bath
GE. HTLV-IH antibody in Edinburgh drug addicts. Lancet
1985; ii: 1129-30.
2 Walsh SS, Pierce AM, Hart CA. Drug abuse: a new problem.
BMJ 1987; 295: 526-7.
3 SeeffLB, Wright EC, Zimmerman HJ, et al. Type B hepatitis
after accidental needlestick exposure: prevention with
hepatitis B immune globulin. Ann Intern Med 1978; 88:
285-93.
4 Marcus R, CDC Cooperative Needlestick Surveillance
Group. Surveillance of health care workers exposed to
blood from patients infected with the human immunodeficiency virus. N EnglJMed 1988; 319: 1117-23.
5 Mitsui T, Iwano K, Suzuki S, et al. Combined hepatitis B
immune globulin and vaccine for postexposure prophylaxis
of accidental hepatitis B virus infection in hemodialysis
staff members: comparison with immune globulin without
vaccine in historical controls. Hepatology 1989; 10:
324-7.
6 Anonymous. Zidovudine in HIV infection. Drug Ther Bull
1991; 29: 81-2.
Surface area estimation: pocket calculator
v nomogram
G L Briars, B J R Bailey
Abstract
Three sheets of 10 surface area determinations were completed by 10 subjects
using a nomogram and a formula. The
formula was faster to calculate, 4-27 v 7-6
minutes for each sheet, and resulted in
fewer serious errors (three v 30 errors).
Methods
Ten volunteer staff from the department of
paediatrics participated in the study. Thirty
paired height and weight measurements from
Surface area has been used to determine the children with cancer (surface area 04-1.7 m2)
dose of chemotherapy drugs for the treatment were divided into sets of 10 and distributed to
of cancer since their introduction for human the volunteers at intervals not shorter than one
subjects and, more recently, to predict bio- week. They estimated the surface area for the
chemical adrenal suppression in children nomogram, and nine months later on a pocket
receiving treatment with inhaled corticos- calculator.
teroids.1 Clinically, surface area is estimated
The volunteers were instructed to record
from measured height and weight, either with a their results to an accuracy that they would use
surface area calculator or a nomogram.2 if the surface area was to be used to determine
Mosteller's simplified pocket calculator the dose of chemotherapy drugs to be given to
formula (surface area (m2) equals the square the child.
It was our intention to compare 'correct use'
root of the expression height (cm) multiplied
by weight (kg) divided by 3600) is a third of the nomogram with the equation.
Nomogram surface area determinations which
alternative.3
The most commonly used nomogram2 was had methodological errors were repeated by
produced by Professor C D West of the the volunteer.
The sample of heights and weights used was
University of Cincinnati. The formula on
which it is based was derived from the data of then enlarged: 199 consecutive surface areas
Boyd.4 Neither the subset of data used by West and the respective heights and weights were
selected from the oncology ward log book.
nor the formula he derived has been published.
(Arch Dis Child 1994; 70: 246-247)
Department of
Paediatric Medicine,
Southampton General
Hospital,
Southampton S09 4XY
G L Briars
Faculty of
Mathematical Studies,
University of
Southampton
B J R Bailey
Correspondence to:
Dr Briars.
Accepted 2 November 1993
The nomogram itself has been validated by
years of safe clinical use. We compared the
Boyd-West nomogram with the Mosteller
equation.
Downloaded from http://adc.bmj.com/ on June 14, 2017 - Published by group.bmj.com
247
Surface area estimation: pocket calculator v nomogram
0.u8
- 11-
0.06
C0
0
.,
U
0.04
.
0.02
A,
0
0
I'
E
a
Ir1
0 0
arl
-
a
o
C
-0-04
,,
0
0O
N
O
01
U-UUL
0
-
0
O
c
C
151 _n
1--
I
A--
a)
O
a 00
000
.0
0
03
E3
E
a)
a)
a
0
0
a)
c
When all 499 paired determinations are considered (figure) the Mosteller formula gives a
result which is a mean of 0 01 1 m2 less than the
13rB
1A
n~~~~~~~~~~~~~~~
t~
+ 2SD nomogram (SD 0-016). On 95% of occasions
the difference (nomogram surface area minus
8° 00
0
Mosteller surface area) will lie between
°32°
°3^@ O3q^RP E3
,3A
Mean -0-021 and 0 044 M2. The differences
_
a
between the two methods were greatest at the
a3 dbo
5
lowest and highest surface areas, and were least
0
W
O'
-2SD around 11 Im2. This curvature is due to
differences between the underlying equations.
00
-0-06
-0.08
0.2
0.4
0.6
0.8
1
1.2
1.4
16
1.8
Mean of methods
Plot of the difference between the nomogram method and Mosteller's method of calculiating
surface area v the mean result for the two methods.
These surface areas (range 0-35-1-80 m2 ) had
been determined from the nomogram b: y one
observer and checked by another. Suirface
areas were later calculated accordin.g to
Mosteller's equation.
All 499 pairs of surface areas were subjjected
to Bland-Altman analysis.
Results
Thirty (10%) errors from 300 determinaitions
were identified. Three were spontane ously
corrected by the volunteer. In three sheei ts (24
errors) the error was systematic. Once m,ade it
was repeated for the remaining determinaations
on the sheet. Errors were of two types andI both
types resulted in a clinically significant undercalculation of surface area. The errors we re (a)
plotting the child's weight in kilograms o)n the
nomogram scale labelled 'weight in po unds'
(29/30 errors) and (b) reading the se cond
decimal place of surface area as the first tlhat is,
reading 1-04 m2 as 1-4 m2.
There was no significant difference i:n the
mean time taken to complete the result s;heets
with and without errors (8-22 v 7-65 mirlutes;
SE 1.31).
Three of 30 formula result sheets cont-ained
one error. One was spontaneously correIcted,
one resulted from the volunteer not pre-ssing
the square root key, and the third vvas a
transcription error.
The nomogram result sheets took a mcLan of
7-60 minutes to complete compared with 4-27
minutes for the formula sheets (SE O-54;
p<OsOO1).
Discussion
The most important finding of this study is the
high frequency of nomogram reading errors.
The volunteers were all familiar with the
nomogram and although they might have
checked their results more carefully had they
been for clinical use, the ease with which these
errors were made reveals a weakness in the
method.
Adjacent scales showing weight in kilograms
and pounds makes it too easy to make a
clinically significant underestimate of the
child's surface area, with the risk of ineffective
chemotherapy treatment for cancer. The three
mistakes that occurred in the calculated
surface areas highlight the value of an independent double check.
Most published surface area equations are
equally consistent with the data from the
largest study4 to measure surface area by direct
methods (Bailey and Briars, unpublished).
This alone might justify the clinical use of any
of these methods, but the widespread use of
the Boyd-West nomogram demands that this is
taken as the clinical standard.
The Mosteller formula can be used interchangeably with the nomogram when an
underestimate of 0044 m2 or an overestimate
of 0021 m2 is not of clinical significance. It
can be used with safety in all patients receiving
treatment with inhaled corticosteroids because
the smallest daily dose change of 50 ,ug is so
large when corrected for surface area that
differences between the nomogram and
formula are insignificant.
1 Priftis K, Milner AD, Conway E, Honour JW. Adrenal
function in asthma. Arch Dis Child 1990; 65: 838-40.
2 Vaughan VC III, McKay RJ, eds. Nelson textbook of pediatrics.
Philadelphia: Saunders, 1975: 1713.
3 Mosteller RD. Simplified calculation of body surface area.
NEnglJMed 1987; 317: 1098.
4 Boyd E. The growth of the surface area of the human body.
Minneapolis: University of Minnesota Press, 1935
Downloaded from http://adc.bmj.com/ on June 14, 2017 - Published by group.bmj.com
Surface area estimation: pocket calculator v
nomogram.
G L Briars and B J Bailey
Arch Dis Child 1994 70: 246-247
doi: 10.1136/adc.70.3.246
Updated information and services can be found at:
http://adc.bmj.com/content/70/3/246
These include:
Email alerting
service
Receive free email alerts when new articles cite this article. Sign up in the
box at the top right corner of the online article.
Notes
To request permissions go to:
http://group.bmj.com/group/rights-licensing/permissions
To order reprints go to:
http://journals.bmj.com/cgi/reprintform
To subscribe to BMJ go to:
http://group.bmj.com/subscribe/