Page 60 - JSOM Winter 2018

FIGURE 1 Study design by group. FIGURE 2 Vertically paired images of the band-only, the bone, and
the boneless groups.
(A) (C) (E)

(B) (D) (F)

(A) Segment of a green noodle is shown at an angle, with a wood
dowel at the center and a blue tourniquet applied without a turn of
the rod. This is the band-only group, or the negative control, setup, a
not turned. The band-only group was similar to the boneless state without compression because the rod is not turned, so the band
group except the bone remained inserted while the rod was not is not tightened. The tourniquet rests on but does not squeeze the limb
turned. This setup was common among groups as the baseline surface inward. At the bottom is a ruler. Note that the rod is located
for reference (Figure 2A, 2B). The positive control group was as it is before turning: centered over the band, and overhanging the
called the bone group, and it comprised data from simulated band edge transversely by 2–2.125 inches. Users of this visual cue can
routine clinical use of the tourniquet to stop the bleeding when gauge if the band is 2–3 inches above the wound. (B) The diagram de-
picts the limb end-on. In cross-section, the limb under the tourniquet
the bone is intact (i.e., neither fractured nor lost). The bone includes soft tissues and bone. The blue tourniquet encircles the limb,
group was like the band-only group but the rod was turned. the innermost circle is the bone, whose contents are manila colored,
and the soft tissues are in between in a peach color. This is band-only
group, or the negative control, setup. The limb and bone in cross-sec-
The objective of the comparison of the bone group (Figure 2C, tion are not quite circles, because they are ellipses. The end-on view
2D) with the boneless group (Figures 2E, 2F, 3) was to delin- shows area and not volume, but changes in both are proportional.
eate the effect of bone loss. Three panels (B, D, and F) are to scale. (C) This is the bone group,
the positive control setup. The rod has been turned and secured. The
Because compression affects bone and soft tissues differently, applied tourniquet squeezed the underlying soft tissues, making their
sampling was performed in two ways for the limb and its tis- volume less. An outer caliper depicts measurement of an axis distance
between two points on the surface of the soft tissues at the left edge
sues, to delineate where compression works. We bought the of the tourniquet. Past the tourniquet edge, the squeeze effect tapers
pool noodle, a buoyant, flexible cylinder of polyethylene foam off. (D) The diagram depicts the boneless group, the positive control
used as an aid in staying afloat in water (used for the model), setup, a state with compression. The tourniquet squeezed the soft tis-
locally at summer’s end when we were offered a discounted sues 17% smaller by volume. The bone is unchanged in size, but the
soft tissues are squeezed to a smaller size by a few millimeters from its
rate. The noodle (Mega Noodle, swimways.com) represented original limb profile, as in the band-only group. Again, the limb and
soft tissues like skin, fat, fascia, muscles, nerves, and blood bone shapes are ellipses. (E) The study group setup had the tourni-
vessels. The thigh-wide noodle had a circumference of 37.1cm quet squeezing the soft tissues, which collapsed inward into the void,
(major axis, 121mm; minor axis, 113mm). The noodle tunnel the central tunnel of air that was rendered into an obviously elliptical
was central along its longitudinal axis. The tunnel width was shape. An inner caliper is shown in measurement of an axis length.
Without bone support, the limb surface is squeezed a bit more by a
that of a thigh bone. We cut the noodle transversely with a few millimeters (mean, 3mm or 3% [3mm/103mm]) than when bone
knife into cylindrical segments. The segment for tourniquet was present (panel C, band-only group). (F) The boneless group dia-
use had a height of 65mm. In the bone group, a wood dowel gram depicts the squeezed soft tissues, which collapsed inward into
representing bone was fitted into the tunnel (Figure 2A, 2C). the void (white region). Without bone support, the limb surface is
squeezed a bit more by a few millimeters than when bone was present
The fit withstood gravity’s pull, but the dowel was easily in the bone group and also than when the limb profile was uncom-
pushed in or out of the tunnel without stretching the tunnel. pressed in the band-only group.
The cross-sections of the tunnel and thigh were not quite cir-
cular; rather, they were truly elliptical (Figure 3). axes were divided by 2. In this way, a denominator of 4 (M/2
× m/2) was used to make the M × m result analogous to the
3
We represented the geometry of the segment under the tourni- familiar circle value, r . To convert mm to mL, we divided by
2
quet as a cylinder, and because the dimensions of thighs and 1,000:
noodles were elliptical in cross-section, we used an elliptic cyl- (π × M × m × h)
inder. In this model, the longitudinal axis of the cylinder was Volume = 4 / 1,000 (Equation 1)
perpendicular to the cross-sections. The limb volume under
the tourniquet included soft tissues and bone or no bone (a Axis distances (M and m) were measured in millimeters, using
void). The tourniquet was 40mm wide. The equation to calcu- a ruler or caliper (caliper types: 8" inside, 8" outside; bighorn
late the volume of this type of cylinder included the constant corp.com). Measurements were oriented to the tourniquet
π (approximately 3.14), the 40mm height (h) of the cylinder, edges because those defined the width of applied compression.
as well as a major axis (M) and a minor axis (m) of the ellipse.
The ellipse axes were perpendicular to each other. The cylin- At a tourniquet edge, we drew with a pen two marks to point
der volume was the ellipse area multiplied by the height. For out where to measure, and the marks were perpendicular to
reader ease in mimicking the familiar radius (r) of a circle, the each other because one was aligned on the major axis and

58 | JSOM Volume 18, Edition 4 / Winter 2018