Pressure ulcer risk assessment in critical care: interrater reliability and validity studies of the Braden and Waterlow scales and subjective ratings in two intensive care units

Background: The application of standardized pressure ulcer risk assessment scales is recommended in clinical practice.

Objectives: The aims of this study were to compare the interrater reliabilities of the Braden and Waterlow scores and subjective pressure ulcer risk assessment and to determine the construct validity of these three assessment approaches.

Design: Observational.

Settings: Two intensive care units of a large University Hospital in Germany.

Participants: 21 and 24 patients were assessed by 53 nurses. Patients' mean age was 69.7 (SD 8.3) and 67.2 (SD 11.3).

Methods: Two interrater reliability studies were conducted. Samples of patients were assessed independently by a sample of three nurses. A 10-cm visual analogue scale was applied to measure subjective pressure ulcer risk rating. Intraclass correlation coefficients (ICC) and standard errors of measurement (SEM) were used to determine interrater reliability and agreement of the item and sum scores. Pearson product moment correlation coefficients (r) were used to indicate the degree and direction of the relationships between the measures.

Results: The interrater reliability for the subjective pressure ulcer risk assessment was ICC(1,1)=0.51 (95% CI 0.26-0.74) and 0.71 (95% CI 0.53-0.85). Interrater reliability of Braden scale sum scores was ICC(1,1)=0.72 (95% CI 0.52-0.87) and 0.84 (95% CI 0.72-0.92) and for Waterlow scale sum scores ICC(1,1)=0.36 (95% CI 0.09-0.63) and 0.51 (95% CI 0.27-0.72). The absolute degree of correlation between the measures ranged from 0.51 to 0.77.

Conclusions: Interrater reliability coefficients indicate a high degree of measurement error inherent in the scores. Compared to subjective risk assessment and the Waterlow scale scores the Braden scale performed best. However, measurement error is too high to draw valid inferences for individuals. Less than 26-59% of variances in scores of one scale were determined by scores of another scale indicating that all three instruments only partly measured the same construct. The use of the Braden-, Waterlow- and Visual Analogue scales for measuring pressure ulcer risk of intensive care unit patients is not recommended.