Management of wound fluid is an important component in pressure ulcer treatment. In order to select appropriate dressings, it is necessary to evaluate wound fluid volume accurately; however, traditional methods based on the frequency of gauze change or its weight are semi-quantitative with limited precision. The purposes of this study were to reveal the distribution of wound fluid volume of full-thickness pressure ulcers and to develop a quantitative algorithm to estimate wound fluid volume using wound characteristics. A cross-sectional study was conducted for older patients with full-thickness pressure ulcers. Thirty-six patients with 44 pressure ulcers were included in the analyses. Wound fluid was collected in a polyurethane film dressing and its volume was measured as a reference. The median volume（range）of wound fluid of pressure ulcers was 4.2（0.1-47.0）ml/day. Using a general linear model, the traditional method using gauze-change frequency did not show adequate accuracy（R2=0.44）. The most accurate model provided five classes combined with the frequency of gauze change, DESIGN-R total score classified by 22 points, and the healing process（R2=0.67）. The least squares mean（95% confidence interval）of estimated wound fluid volume（ml/day）was 0.2（0.1-0.4）for class I; 1.2（0.6-2.2）for class II; 4.7（2.2-10.0）for class III; 7.3（3.4-15.7）for class IV; and 27.3（9.8-76.0）for class V. The developed algorithm to estimate wound fluid volume quantitatively will contribute to standardize the selection of suitable management options for full-thickness pressure ulcers.
An effective method of preventing pressure ulcers is to use mattresses. Air mattresses have high potential to redistribute pressure but are supposed to be less comfortable, since they cause deep immersion of the buttocks, leading to excessive spinal curvature and a bad sleeping posture. In this study, we developed an air mattress with a function called the Fitting Mode, which is expected to prevent deep immersion of the buttocks. Each air cell of this air mattress is controlled independently, so the inner air cell pressure can be set separately. We evaluated this mattress by measuring the degree of immersion and interface pressure in the supine position in 23 subjects（11 males and 12 females; 30.1±7.4 years）. While subjects were lying on the mattress, data were collected in either Fitting Mode（+） or Fitting Mode（-）, under four phases of inner air cell pressure: default（4 kPa）, -0.8 kPa, -1.6 kPa, and -2.4 kPa. At every setting of inner air cell pressure, the buttocks were immersed deeper in Fitting Mode（-） than Fitting Mode（+）. By setting inner pressures of -0.8 kPa, -1.6 kPa and -2.4 kPa, the interface pressure of the buttocks area was higher in Fitting Mode（+） than Fitting Mode（-）, but each interface pressure was under the risk value of pressure ulcer development. Fitting Mode can prevent deeper immersion of the buttocks while maintaining the ability to redistribute pressure.