Objective: To develop a simple, reproducible validation test protocol for classification of air-loss support systems.
Design: Simultaneous experimental measurement of moisture loss and temperature reduction at the air-loss support surface-human body equivalent interface 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 placed 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 interface initiated. After the dry moisture reservoir came to temperature equilibrium for 30 minutes, it was replaced with a wet one that was saturated with 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 evaporation 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 for average temperature reduction (p <.017) and for standardized rate of moisture loss (p =.0001). The measured temperature change at any instant of time reflected the effect of evaporation and the opposing effect of thermal conductivity.
Conclusion: Measurements of support interface climate change allowed for selective grouping of LAL surfaces according to rate of moisture evaporation and the resulting temperature reduction. Neither temperature change nor evaporation rate alone was sufficient to determine the microclimate characteristics of the support surface. Combined, these characteristics can effectively describe the performance of any LAL support system and may be used to define standards of performance.