Pressure sores or pressure ulcers (PU) are a major health concern in both acute and long-term care facilities causing pain and discomfort to the affected person. A PU is a localized damage to the skin and underlying tissue typically over bony prominences, such as sacrum, coccyx, heels, and hips regions due to pressure with or without shear (1). Risk factors include advanced age, immobility, malnutrition, vascular diseases, incontinence, and other skin conditions (2).
The prevalence varies depending on the risk population and tested setting. A hospital survey in United States acute care setting (n = 216,626) reported pressure injuries prevalence of 9.2 % (n = 19,893). The reported prevalence for the German long-term care setting was 2 % to 5 % and in hospitals 2 % to 4 % (starting at category 2). Routine surveys in the hospital sector provided heterogeneous data with prevalence of 0.07 % to 4.37 % from category 1 and 1.6 % from category 2 (3). In Austria, the hospital-acquired pressure ulcer prevalence was 0.6 % (n = 3,648) in hospitals and 3.5 % (n = 696) in nursing homes for the year 2012 (4). Between 2008 and 2012, the reported prevalence in long-term care facilities in Germany were between 4.8 % and 73.3 % (n = 14,798) depending on additional health conditions such as urinary incontinence and malnutrition (5).
Nurses play a key role in recognizing patients at risk for developing PU through their regular assessment and continuity of patient care. Standardized screening instruments, such as the Braden Scale for Predicting Pressure Sore Risk (Braden Scale) (6), may assist nurses in identifying PU risk in order to initiate preventive interventions or treat existing wounds (7).
The Braden Scale is based on the conceptual model by Braden and Bergstrom (8). Determinants and factors contributing to PU development are pressure intensity, pressure duration as well as tolerance of the skin and underlying tissues for pressure. The conceptual model underlying PU development is displayed in figure 1.
The factors mobility, activity, and sensory perception may contribute to prolonged Pressure exposure. The factors moisture, friction and shear are extrinsic factors, while the factor nutrition is an intrinsic factor. The extrinsic and intrinsic factors influence Tissue Tolerance (8). Mobility refers to the diminished ability of a person to alternate or control their body position. Activity describes a person’s ability to move independently and thus, avoid prolonged pressure over bony prominences (e.g. sitting in a wheelchair or being bedridden). Sensory perception refers to a person’s reduced ability to perceive an uncomfortable position and change their position accordingly. The extrinsic factor friction and shear forces are demonstrated by a person’s inability to lift their body during a position change. The component of the extrinsic factor moisture refers to a person’s exposure to moisture (e.g. urinary and/or fecal incontinence, perspiration). The component of the intrinsic factor nutrition comprises the intake of food in order to nourish the body and support the quality and integrity of soft tissue (8).
The Braden Scale, as displayed in figure 2, consists of six subscales to evaluate sensory perception, activity level, mobility, nutrition status, skin moisture, and friction and shear forces to assess the risk of PU. The subscales are rated independently according to the observed severity from 1 to 4 points except for the subscale friction and shear, which is ranked from 1 to 3 points (9). Hence, the total score can range from 6 to 23 points (19 to 23 points, not at risk). The lower the score, the higher the PU risk for a patient (6). Several different cut-off points have been reported. Frequently, a score of 9 or lower indicates very high risk, 10 to 12 points high risk, 13 to 14 points moderate risk, and 15 to 18 mild risk to develop a PU (7).
The Braden Scale’s psychometric properties have been tested with different methods of classical test theory. The literature review revealed evidence that the Braden Scale is valid, reliable, feasible, and applicable for different populations and settings (5-7, 10).
The interrater reliability and interrater agreement (Po) for the Braden Scale (11) were high in two different nursing home samples collected in 2007 and 2008 (in 2007: n = 288, Po = 0.66, ICC(1.1) = 0.90, CI 95 % [0.88; 0.92], standard error of the mean (SEM) = 1.00; in 2008: n = 292, Po = 0.63, ICC(1.1) = 0.88, CI 95 % [0.85; 0.91], SEM = 0.98). The 95 % limits of agreement were -2.8 to 2.8 (2007) and -2.7 to 2.7 (2008). The most frequent measurement errors were obtained for the subscales moisture, sensory perception, and nutrition (11).
In a Meta-analysis by Park et al. (7), the pooled sensitivity and specificity were 0.72 (CI 95 % [0.69; 0.74]) and 0.63 (CI 95 % [0.62; 0.64]), and the summary receiver-operating characteristic area under the curve was 0.84 (SE = 0.02). The heterogeneity indexes in sensitivity and specificity were 79.9 % (χ2 = 119.57, p < 0.001) and 96.4 % (χ2 = 673.34, p < 0.001), which indicates moderate to high heterogeneity across the 25 included research studies. The positive Likelihood ratio was 2.31 (CI 95 % [1.98; 2.69]) and the negative Likelihood ratio was 0.43 (CI 95 % [0.06; 0.51]). This resulted in an odds ratio of 6.50 (CI 95 % [4.64; 9.11]) indicating that the odds of a diagnosed PU increase by 6.50 with the determined risk of a PU with the Braden Scale (7).
Although the Braden Scale has been tested extensively, there is limited information on the construct validity available. The convergent construct validity was tested between the mobility subscale and physical activity measured by the Motionlogger Actigraph (12). Analysis revealed that higher subscale scores are related to more physical activity (F = 31.69, p < 0.001). Omolayo et al. (9) studied if the construct validity of the Braden moisture subscale is inversely related to the observable contact to moisture (i.e. wet or soiled briefs, frequency of brief changes). The results of the ANOVA revealed significant differences among the moisture subscale and wet observations (F = 8.78, p < 0.001) and among the moisture subscale and frequency of brief changes (F = 4.26, p < 0.0057). The moisture subscale was significantly correlated with frequency of wet observations (rho = -0.233, p < 0.001) and soiled observations (rho = -0.133, p < 0.013). This indicates a higher subscale score with reduced wet or soiled observations. The inverse but not significantly correlation between the moisture subscale and frequency of brief changes was slightly negative (rho = -0.105, p < 0.518) (9).
Recently, the construct validity of the Braden Scale was tested by Chen et al. (13) in a retrospective analysis of consecutive patients (n = 2,625) with structural equation modeling (SEM) to reveal the relationship between the latent variable (Braden Scale total score) and measurement variables (Braden Scale subscale scores) as well as the explained variance in the measurement variables. The proposed model was maintained by χ2(9) = 22.854. The comparative fit index (CFI = 0.902), goodness of-fit index (GFI = 0.974), and the root mean square error of approximation (RMSEA = 0.092) indicated an insufficient model fit. The factor loadings of the subscales were significant; therefore, the construct validity of the Braden Scale was not confirmed in a hospital setting (13).
There is scarce research on the factor structure of the scale’s variables. The literature search revealed no other study using structural equation modeling (SEM) to test the construct validity of the Braden Scale in the long-term care setting in Austria. Therefore, this study aimed to test the construct validity of the Braden Scale with SEM in the long-term care setting in Austria.