Objective: To develop a simple, reproducible validation test protocol for c
lassification of air-loss support systems.
Design: Simultaneous experimental measurement of moisture loss and temperat
ure reduction at the air-loss support surface-human body equivalent interfa
ce from a sweating human skin analogue.
Setting: A hospital department of physical medicine and rehabilitation.
Other Participants: These 3 manufacturers contributed 14 support surfaces.
Interventions: Test support surfaces and a standard foam mattress were plac
ed on a hospital bed. Water was circulated to a loading gauge, placed on a
dry moisture reservoir, and connected to a water bath to keep the interface
at 37 degrees +/- 0.5 degrees C. The loading gauge and support surface was
adjusted 23cm below the water bath level and the air flow through the inte
rface initiated. After the dry moisture reservoir came to temperature equil
ibrium for 30 minutes, it was replaced with a wet one that was saturated wi
th 36g of saline. The temperature change and evaporation rate were recorded
throughout a 90-minute test period.
Main Outcome Measures: Temperature of support surface interface and evapora
tion rate.
Results: Clustered data from temperature reduction and standardized rate of
moisture loss yielded 3 groups of support surfaces in categories of no air
loss (control), low air loss (LAL), and high air loss. The mean values of
the characteristic temperature reduction and rate of moisture loss differed
significantly between the groups. By multiple comparisons with Bonferroni'
s adjustment, the group means differed significantly fur average temperatur
e reduction (p <.017) and for standardized rate of moisture loss (p =.0001)
. The measured temperature change at any instant of time reflected the effe
ct of evaporation and the opposing effect of thermal conductivity.
Conclusion: Measurements of support interface climate change allowed for se
lective grouping of LAL surfaces according to rate of moisture evaporation
and the resulting temperature reduction. Neither temperature change nor eva
poration rate alone was sufficient to determine the microclimate characteri
stics of the support surface. Combined, these characteristics can effective
ly describe the performance of any LAL support system and may be used to de
fine standards of performance.