Changes in transcutaneous oxygen tension as a result of prolonged pressures at the sacrum

Prolonged pressures at the patient support interface can lead to the impairment of tissue viability resulting in tissue breakdown, particularly in debilitated individuals. However there are still few clinical guidelines to indicate safe levels of pressure and time for individual tissue areas. The effects of extended loading on transcutaneous oxygen tension (tcPO2) were examined at the sacrum of twenty debilitated subjects, prone to tissue breakdown. Each load was applied for a ten minute period through an indenter incorporating a commercial oxygen electrode. Loads were incremented until the tcPO2 levels were reduced below 2.7 kPa (20 mmHg), at which time the tissue was unloaded. The interface pressure for each applied load was measured. Results are presented in terms of relating applied pressure and time to relative changes in tcPO2. When all the results are combined it is clear that there is a range of applied pressures which significantly reduce the tcPO2 levels. The applied pressures to produce, for example, 50% reduction of the unloaded resting value, ranged from 3.0 kPa (22 mmHg) to 12.2 kPa (92 mmHg). This indicated the individual nature of the tissue response, which should be determined before clinical guidelines of safe pressure levels are established.