BIMECO/
Bioscience Research Institute - Limb Volumes Professional
|
| Research Update #1 - Estimating Limb Volume via
Circumferential
Measurements |
| This issue considers the
question of choosing the number of limb
circumference
measurements to monitor, track and document limb volume changes. Hand
and foot volume considerations are discussed in Update
#2. If you
wish you may go directly to the take
home messages |
| Limb Volume Estimates are
Needed
to Access and Document Therapy Effectiveness Measurement
and
documentation
of limb volume changes during the course of lymphedema therapy is an
important
part of the therapeutic process for the patient, the therapist, the
physician
and often for reimbursement agencies. The most commonly used method
relies
on the simple tape measure which is used to systematically measure limb
circumferences at strategic sites along the limb. These circumference
measurements,
sometimes referred to as girth measurements, are then used to calculate
the volume of the limb over the region of interest (1).
Although this method actually estimates limb volume rather than
directly
measuring it (2),
earlier research studies have
shown
that, when properly done, the limb volumes that are calculated compare
favorably with those that are measured either with water displacement (3)
or estimated with more sophisticated automated techniques (4). |
Limb
Volume
Estimates Depend on the Model Used Because a limb is
not a
nicely
defined geometric shape, use of girth measurements to estimate limb
volume
requires an assumption about the actual shape of the limb. A commonly
used
model assumes that the limb can be sub-divided into a number of
separate
segments, each of which, if small enough, can be represented by the
geometrical
shape known as a frustum.
Since the volume
of a frustum depends only on its proximal and distal circumferences and
the length of the segment between these circumferences, simple tape
measure
measurements can be used to evaluate the segment's volume. Then, by
adding
together the calculated volumes of all of the limb's segments, the
total
volume of the limb can be estimated.
|
| Accuracy of Limb Volume
Estimates
Depend on the Number of Segments Used Assuming that
each
circumference
measurement could be made precisely and without error, the
theoretically
best estimate of limb volume would be obtained using the most
circumference
measurements practically possible. This choice however is not
clinically
useful because of the time involved for so many measurements. So, how
does
one determine the minimum number of circumference measurements that are
suitable to adequately estimate limb volume? Recent research offers
some
answers. |
Circumference
Measurements at 4-6 Centimeter Intervals May Be Optimal Estimates of limb
volume
using tape measure circumference measurements at 4 cm intervals were
compared
with estimates made using automated optical methods in a 142 legs and
42
arms in patients with lymphedema (5).
Results
showed a strong correlation between these measurement methods; 0.98 for
legs to 0.96 for arms. Moreover, the percentage difference between limb
volumes estimated by the two methods was less than 5% for legs and less
than 7% for arms. Tape measure measures tended to slightly
underestimate
the volume of both arms and legs. However, in cases of unilateral limb
edema (arm or legs) estimates of actual percentage edema were found to
be nearly identical for each of method. Arm volumes measured by the
"gold-standard"
water-displacement method have also been compared with volume estimates
using limb circumferences at 3, 6 and 9 cm. intervals in 50 persons
with
arm lymphedema (6).
Results of this research
also
showed an excellent correlation between methods (0.97-0.98) and, based
on considerations of the standard error of the data set, these authors
suggested a best arm volume estimate is obtained if circumference
measurements
are made at six cm intervals. However, the data also indicated
that
measurements at 3 cm intervals resulted in lowest (best) value for the
limit of agreement between the geometric and water displacement
methods.
These authors also demonstrated that the geometric frustum model
slightly
underestimates arm volume. Other workers have recently confirmed the
close
correspondence between water displacement and cirumference methods for
arm volume estimation using 4 cm intervals (7).
|
Summing
Up: The Take Home Messages Estimating limb
volumes
via
circumference measurements applied to the frustum model is probably the
most widley used clinical method. Recent research findings, combined
with
other published information, indicate that for this method, a near
optimum
compromise between time requirements and accuracy for limb volume
estimations
is to use intervals of 4-6 centimeters. It is noteworthy that although
correspondence between methods is excellent, absolute values of volume
obtained using the frustum model tends to be less than that obtained
with
either water displacement or automated optoelectronic methods. This
slight
deviation is of little clinical importance since the most important
aspect
is to monitor, document and report limb volume changes. This is
very reliably accomplished using the frustum model. In the past the
process
of calculating all of the segmental volumes needed to estimate limb
volume
and keep track of the segment-to-segment and total limb volumes as well
as percentage edema changes, was tedious, time consuming and loaded
with
potential calculation errors. Fortunately, an inexpensive software
package
is now available that does it all for us automatically!
For those
interested,
a free trial version can be downloaded.
|
We hope that
you have found this research update
useful.
We would appreciate hearing from
you as to any comments
or thoughts you may have regarding future topics of specific interest
to
you. Any comments may
be sent to support@limbvolumes.org
1.
Casley-Smith JR. Measuring and representing peripheral oedema and its
alterations.
Lymphology.
1994;27:56-70
2.
Sitzia J. Volume measurement in lymphoedema treatment: examination of
formulae.
Eur J Cancer Care. 1995;4:11-16
3.
Tierney S, Aslam M, Rennie K, Grace P. Infrared optoelectronic
volumetry:
the ideal way to measure limb volume.
Eur
J Vasc Endovasc Surg. 1996;12:412-417
4.
Sukul K, den Hoed PT, Johannes EJ, Van Dolder R, Benda E. Direct and
indirect
methods for the quantification of leg volume: comparison between water
displacement volumetry, the disk model method, and the frustum sign
model
method, using the correlation coefficient and the limits of agreement.
J
Biomed Eng. 1993;15:477-480.
5.
Mayrovitz HN, Sims N, Macdonald J. Assessment of limb volume by manual
and automated methods in patients with limb edema and lymphedema. Advances
in Skin & Wound Care. 2000;13:272-276
6.
Sander AP, Hajer NM, Hemenway K, Miller AC. Upper-extremity volume
measurements
in women with lymphedema: a comparison of measurements obtained via
water
displacement with geometrically determined volume. Phys
Ther 2002;82:1201-1212
7.
Karges JR, Mark BE, Stikeleather SJ, Worrell TW. Concurrent validity of
upper-extremity volume estimates: comparison of calculated volume
derived
from girth measurements and water displacement volume. Phys
Ther 2003;83:134-145
Return
to text
Table 1. Comparison of Automated
Opteoelectronic
vs. Frustum Estimated Limb Volumes
|
Limbs (N=184)
|
Automated Volume (ml)
|
Frustum Model (ml)
|
Percentage Difference
|
Correlation Coefficient
|
|
Legs (n=142)
|
7160 +/- 170
|
6900 +/- 170
|
4.14 +/- 0.54
|
0.98
|
|
Arms (n=42)
|
2700 +/- 90
|
2530 +/- 90
|
6.97 +/- 1.18
|
0.96
|
Data from reference
5. Return
to
text
Last updated 01/31/ 2010