Prado CBC, Machado EAS, Mendes KDS, Silveira RCCP, Galvão CM.
In non-randomized studies
(24-25)
, low-prole alternating
pressure overlap was investigated (Dabir Micropressure
Operating Table Surface
®
, Dabir Surfaces, Chicago, Illinois,
USA). In a randomized controlled trial
(21)
, the surface
tested was an alternating air cushion from the Chinese
manufacturer WeXuan Co.
In four studies, the results showed the superiority
of a high-tech support surface in relation to low-tech
surfaces in the prevention of PI in the intraoperative
period
(17,21,24-25)
. In a randomized controlled trial
(19)
, the
experimental group (high-tech support surface) had
a lower incidence of PI (2/98) than the control group
(7/100), however, there was no statistically signicant
dierence between the groups (p=0.172).
In conducting the two non-randomized studies
included in the review, there are similarities in terms
of research design, population and tested support
surfaces
(24-25)
. In both, in the experimental group, low-
prole alternating pressure overlay was tested. This
overlay incorporates hundreds of supporting nodules
arranged in rows that periodically inate with air, so the
patient’s weight is distributed over small nodal points of
alternating contact. Alternate rows are interconnected
so that the overlay has two areas that are alternately
inated. Ination/deation of the rows is computer
controlled and provides temporary localized relief of
micropressure in areas of the body lying above deated
nodules. The overlay was placed on top of the standard
operating table mattress, before starting the surgery.
The operating room is considered as a place of risk
for the development of PI, due to strict restrictions specic
to the environment, namely: the inability to reposition
the patient during the anesthetic surgical procedure for
pressure relief and the need of permanence on a stable
support surface, generally implying the use of a relatively
rigid padding material, resulting in the exposure of the
body to tissue deformation conditions. In this context, low-
prole alternating pressure overlay was designed for use
in surgery, which brought technological advances in a eld
in which contemporary technology is generally poor
(26)
.
In the last category (comparison between low-tech
support surfaces) two non-randomized studies
(22-23)
and
one randomized controlled trial were included
(18)
. In a
non-randomized study
(22)
, two operating table mattresses
and an overlay of dry viscoelastic combined in dierent
ways were tested with the participation of 505 patients
(divided into six groups). Regarding PI development, dry
viscoelastic polymer overlay was more eective than foam
and gel or standard mattresses.
In the other non-randomized study
(23)
, two support
surfaces were tested on the same patient, and on the
right side a high-density foam pad (32 kg/m
3
), 50%
resilience and 10 cm thickness was applied (chest and iliac
crest) and on the left side the viscoelastic polymer pillow
(Action
®
, model 40700; Action, Hagerstown, Maryland,
USA), two-cm-thick, also on the chest and iliac crest.
Mean pressures and peak pressures were signicantly
lower at the points evaluated with the viscoelastic polymer
pad, compared to the points tested with the high-density
foam pad. However, the results did not show a statistically
signicant dierence in the incidence of pressure injury
between the two support surfaces tested (OR=0.47, 95%
CI, 0.11-1.99).
In the randomized controlled trial
(18)
, also included in
this category, patients in the control group used devices
according to the criteria of each nurse. Options included
gel pads, egg box foam mattress and “foam donuts”
for heels and elbows. The patients in the intervention
group were placed on a special foam cover with a 25%
indentation force (IF) of 30 pounds and a density of
1.3 (specication considered ideal). The number of
participants in the experimental group (55/206) showed
signicantly higher occurrence of PI than those in the
control group (34/207) (p=0.0111), indicating that the
special foam surface that was tested was not eective in
preventing this type of injury.
The standard surgical table mattress is usually made
of two-inch (5.08 cm) elastic foam and covered with black
vinyl fabric. Despite its excellent stability, there is evidence
that this type of surface contributes to the development
of PI. On the other hand, mattresses made with high-
specication foam can reduce the development of this
type of injury. Thus, the multi-layer smooth surfaces
allow the patient to sink into the underlayer and wrap
around the body to increase the contact area by up to
60%. Such properties help to distribute pressure over
a larger area. Bi-elastic layers also reduce skin creases
and shear forces
(27)
.
The support surface must have the best
characteristics to provide eective pressure redistribution,
which are: lowest mean interface pressure, lowest peak
interface pressure and highest skin contact area. Based on
these assumptions, researchers conducted a comparative
descriptive study with volunteers to investigate four types
of support surfaces, with the aim of identifying the most
eective surface for pressure redistribution in prolonged
surgical procedures. The surfaces tested were: a) standard
surgical table surface, made of three-layer viscoelastic
foam; b) static air-inated seat cushion that was used
under the sacral area and placed on the standard surgical
table surface; c) two-layer surgical table surface, with
the upper layer of gel and the lower layer of high-density
foam; d) surgical surface for simulating uid immersion.
The results indicated that, although all surfaces had similar
mean interface pressures, the air-inated static seat
cushion had the best pressure redistribution properties