Commentary on Sayar S et al. (2009) Incidence of pressure ulcers in intensive care unit patients at risk according to the Waterlow scale and factors influencing the development of pressure ulcers. Journal of Clinical Nursing 18, 765-774.

Well designed studies on the incidence of pressure ulcers and risk factors for pressure ulcer development in intensive care unit (ICU) patients are still rare (Keller et al. 2002, Shahin et al. 2008). Sayar et al. (2009) have made an important contribution to this topic. They aimed to determine the pressure ulcer incidence in three ICUs and influential factors for pressure ulcer development. Their prospective design was especially useful for identifying factors that may cause subsequent pressure related tissue breakdown. However, before interpreting results and drawing conclusions some points should be considered. Sayar et al. used the Waterlow scale to decide whether the person was at risk or not at risk for pressure ulcer development. Patients not at risk according to that scale and the chosen cut-off point were excluded from the study. It seems logical to focus on ‘at risk’ patients because it can be assumed that they are more vulnerable to pressure related injuries, but this procedure may obscure the relation between risk factors and pressure ulcer development. Among many others, the Waterlow total score comprises information regarding age, gender, incontinence, mobility (e.g. apathetic), neurological deficiencies like paraplegia or surgery. These are exactly the risk factors that, independently, were deemed important by the authors and, therefore, were documented on a separate data collection form. Therefore, the question arises whether there was an interaction between the Waterlow sum scores and the investigated risk factors. In other words, it is not logical to first stratify a sample according to ‘Waterlowrisk-factors’ like age, gender or incontinence and then to try to determine whether these variables were risk factors. Stratification makes the sample within each stratum more homogenous (Szklo & Nieto 2007). This may have been one reason why, in Sayar et al.’s study, there was no association between age, gender or incontinence. Other investigated risk factors, like laboratory parameters or type or characteristic of beds or mattresses not included in the Waterlow scale, may also have been affected in a similar way. When focusing on at risk patients they are, for example, more likely to have a special mattress as compared to not at risk patients. Consequently, the potential influence of the factor ‘mattress’ is limited as the patients of the at risk group are naturally expected to need special equipment. Sayar et al. concluded that the Waterlow scale can be used in ICUs as a tool for assessing pressure ulcer risk because none of the patients regarded as not at risk according to the Waterlow scale developed a pressure ulcer. In the light of the continuing debate regarding the clinical relevance of pressure ulcer risk assessment scales, this interpretation is surprising (PancorboHidalgo et al. 2006, Anthony et al. 2008). In general, the nonoccurrence of new pressure ulcers does not mean that the person was not at risk and vice versa (Defloor & Grypdonck 2004, Anthony et al. 2008). Using pressure ulcers as the external criterion for validating, pressure ulcer risk estimation is limited. Disregarding this limitation does also not justify Sayer et al.’s conclusion: Of 235 patients admitted to the ICUs, 140 were regarded at risk according to the Waterlow scale. Of these, 20 patients developed at least one pressure ulcer. Based on these figures, the sensitivity was 100%, whereas the specificity was 44%. The positive likelihood ratio was 1AE8 indicating that the clinical value is not convincing (Pritts et al. 1999, Deeks 2001). Further, these results go very well along with previous research findings indicating that the sensitivity of