Critical hemoglobin-oxygenation and PO2 of the skin

Abstract

Prolonged mechanical loading can lead to breakdown of skin and underlying tissues which can, in turn, develop into a pressure ulcer. The benefits of pressure relief and/or redistribution to minimise risk have been well documented and these strategies can be provided by employing support mattresses in which internal air pressures can be alternated to minimise the risk of pressure ulcers in patients during prolonged periods of bed-rest. The paper describes the performance of a prototype alternating pressure air mattress (APAM), in terms of its ability to maintain skin viability in a group of healthy volunteers lying in a supine position. In particular, the mattress includes a sacral section supported with alternating low pressure (ALP), with values adjusted to subject morphology, using an in-built pressure sensor. The mattress was supported at four different head of bed (HOB) angles ranging from 0 to 60°. Internal mattress pressures and transcutaneous gas (TcPO2/TcPCO2) tensions at the sacrum and a control site, the scapula, were monitored. Interface pressures were also measured. The sensor was found to be sensitive to the BMI values of the 12 healthy volunteers. In the majority of test conditions the internal support produced sacral TcPO2 values, which either remained similar to those at the scapula or fluctuated at levels providing adequate viability. However in a few cases, associated with a raised HOB angle (≥45°), there was compromise to the skin viability at the sacrum, as reflected in depressed TcPO2 levels associated with an elevation of TcPCO2 levels above the normal range. In all cases, interface pressures at the sacrum rarely exceeded 60 mmHg. Although such studies need to be extended to involve bed-bound individuals, the results offer the potential for the development of intelligent APAM systems, whose characteristics can be adjusted to an individual morphology. Such preventive strategies to maintain skin viability at loaded sites will be designed for subjects deemed to be at high risk of developing pressure ulcers.