International Journal of Nursing Studies
Volume 47, Issue 5 , Pages 531-533, May 2010

Is pressure sore prevention a sensitive indicator of the quality of nursing care? A cautionary note

School of Nursing, University of Auckland, New Zealand

National Nursing Research Unit, United Kingdom

Received 23 December 2009

Article Outline

Keywords: Pressure ulcers, Quality assurance, Quality indicators, Process assessment (health care), Nursing care quality

 

Prevention of pressure ulcers is seen to be a key quality indicator of nursing care and pressure ulcers are widely supported as a nursing sensitive outcome (Van den Heede et al., 2007). It has been suggested as a goal for nationwide quality improvement (McGlynn et al., 2003), and is proposed as an indicator in acute care by the US-based Hospital Quality Alliance from 2010 and in England's NHS (Griffiths et al., 2008) as well as in nursing homes (Nakrem et al., 2009). Underpinning the belief that prevention of pressure ulcers is a quality indicator is the belief that health providers have the means and the tools to take effective action. Underlying this is the assumption that risk assessment tools accurately predict risk, that risk assessment is effective at reducing pressure ulcer incidence and that strategies to escalate management through increasingly complex pressure reduction devices will reduce risk. These processes are often audited in order to determine the quality of care. Yet care processes have not been found to discriminate between institutions with high and low pressure ulcer prevalence (Bates-Jensen et al., 2003). Examination of the evidence reveals how precarious these assumptions are, starting with the assumption that risk assessment tools are accurate.

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1. Do risk assessment tools accurately predict risk? 

Risk assessment tools are used to stratify patients likely to develop pressure ulcers. However, pressure ulcer guidelines recommend risk assessment tools be used as an adjunct to rather than a replacement of clinical judgement (Royal College of Nursing, 2001), principally because the tools cannot accurately and reliably predict patients at risk. The chief factor underlying this performance failure is likely to be that the tools are too simplistic (Papnikolaou et al., 2007), although this simplicity is likely a reason for their popularity in practice. The widely used Braden, Waterlow and Norton scales are all tools that weight scoring components equally, rather than weight the components by the degree to which it contributes risk (Papnikolaou et al., 2007). In addition, components of the scales are often ambiguous, which impacts on the reliability and accuracy of scores (Kottner et al., 2009a, Kottner et al., 2009b). Furthermore, some components require information, such as prior knowledge of the patient's nutritional intake, that may not be available to the assessor at the patient's admission (Cook et al., 1999). Consequently, predictive validity varies wildly. The Braden scale – the best researched tool – has a positive predictive validity of 21–77% (Defloor and Grypdonck, 2004), while the Norton scale varies from 9 to 83% (Defloor and Grypdonck, 2004) and the relatively untested Waterlow scale varies from scale 5 to 7% (Rycroft-Malone and McInnes, 2000).

Admittedly, predictive validity may not be the best way to evaluate the effectiveness of risk assessment tools (Defloor and Grypdonck, 2004), as the patients in validity studies are usually subject to pressure prevention strategies and so intrinsic risk is not being assessed. Predictive validity cannot be properly determined when the probability of the outcome reduces as a result of the prediction. This situation would be the case if risk assessment led to effective preventative actions that reduce pressure ulcer incidence, but is that really the case?

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2. Does risk assessment using risk assessment tools prevent pressure ulcer development? 

Randomised trials of pressure prevention strategies are the most reliable means of assessing their effectiveness, but a Cochrane review found no randomised trials comparing a risk assessment tool to no formal risk assessment or comparing the performance of two tools (Moore and Cowman, 2008). One trial not included by Moore and Cowman did provide some tempting evidence that suggested using a risk assessment tool does not reduce pressure ulcer incidence (Vanderwee et al., 2007). Vanderwee and colleagues randomised 1617 participants in six hospitals in Belgium covering 14 wards (surgery, general medicine and geriatric wards) to a standard prevention strategy (Braden score <17 or presence of non-blanching erythema (NBE)) or to a more declarative strategy of awaiting the presence of NBE alone. If patients scored <17 on the Braden scale or developed NBE they were also randomly assigned to one of two types of pressure reduction devices (alternating pressure mattress or high specification foam constant pressure mattress) in addition to a standardised pressure management protocol. This approach meant that half the patients within each arm of the trial were assigned to each mattress, thus ensuring no difference in the proportions in each arm treated with each mattress. Vanderwee et al. (2007) found no significant difference in the incidence of pressure ulcers (European Pressure Ulcer Advisory Panel – EPUAP – grades 2–4) – 53 participants (6.7%) in the standard strategy group and 56 participants (6.8%) in the NBE only group developed pressure ulcers (absolute risk reduction 0.1%, 95%CI −2.5 to 2.4%).

The investigators did find that the NBE-only approach was associated with significantly greater conversion to EPUAP grade 3 or 4 ulcers, which does suggest a possible benefit from the use of risk assessment tools. However, the finding was derived from a subgroup analysis. Such analyses can lead to spurious inferences because of multiple significance testing and the implicit choices made as to which differences to test (Oxman and Guyatt, 2002). Vanderwee and colleagues reported 18 tests of significance on their dataset. With a 1:20 chance of finding a significant difference from chance alone in each independent analysis there is no way of properly determining from this study whether the significant result is a true result or a chance result. The probability of finding a positive result by chance from 18 independent analyses where there is no real difference is 60%. So what we have is at best some suggestive evidence that is worthy of further investigation in a properly designed trial. Unfortunately, it does not constitute definitive evidence.

Vanderwee and colleagues also found that the use of pressure reduction devices in the standard approach was double that of the NBE only strategy (31.9% vs. 15.5%, absolute risk increase 16.2%, 95%CI 12.3 to 20.4%, number needed to treat 6, 95%CI 5 to 8). These findings suggest that not only do risk assessment tools over-estimate risk, but also they lead to much greater resource use – no doubt at considerable expense to health provider organisations, given the substantial potential for overtreatment. A large longitudinal study of five acute care hospitals in the United Kingdom followed 2507 patients in general medicine, general surgery, orthopaedics, urology, coronary care, acute care of the elderly, rehabilitation, and gynaecology for 29,611 patient-days between 1996 and 1998 (Clark et al., 2002). Clark and colleagues found that overall 71% of the patients were considered at some degree of risk using the Waterlow scale; 29% were classified as “at risk”, 23% were “at high risk” and 19% were “at very high risk”. These data suggest that approximately three out of every four patients admitted to a general hospital would need pressure ulcer prevention strategies if just driven by scores from this risk assessment tool, even though only 20% were dependent or immobile. Assuming that the risk strata exist (even if the numbers allocated to the strata are not accurate), the challenge is how to best manage different levels of risk?

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3. Do escalation strategies prevent pressure damage? 

Escalation strategies increase the frequency, intensity or complexity of interventions with increased levels of risk. For example, a clinical guideline might advocate moving ‘at risk’ patients off standard mattresses and putting ‘very high risk’ patients on alternating pressure mattresses (Royal College of Nursing, 2001). Moving patients off standard hospital mattresses onto high specification foam mattresses may reduce the relative risk of developing a pressure ulcer by about 60% (RR 0.40, 95%CI 0.21 to 0.74) and similarly, moving patients from standard mattresses to alternating pressure mattresses may decrease the relative risk by about 70% (RR 0.31, 95%CI 0.17 to 0.58) (McInnes et al., 2008). However, in the light of these small differences in estimates of effect it is less clear whether alternating pressure mattresses are superior to high specification foam mattresses. Alternating pressure devices have been directly compared to foam overlays, with no significant difference between the two types of device (McInnes et al., 2008), but the trials were small and of poor quality. A large trial compared an alternating pressure mattress with a high specification foam mattress (Vanderwee et al., 2005) found no significant difference in incidence of EPUAP grade 2 or greater pressure ulcers (15.3% vs. 15.6%, absolute risk increase 0.3%, 95%CI −6.5% to 6.9%). Unfortunately the lack of a standard turning regimen on both mattresses means the effect of the different mattresses cannot be isolated and the equivalence in incidence rates may be because of an interaction with turning regimen. However, the trial probably modelled clinical practice, which is to maintain a turning regimen on foam mattresses but not on alternating pressure mattresses. In areas where this difference in regimens is practiced, it may not be necessary to use alternating pressure mattresses where turning and high specification foam mattresses can be used.

Like Vanderwee et al. (2007), the trial by Vanderwee et al. (2005) is also suggestive. Health providers may be wasting resource on the more expensive forms of pressure ulcer prevention, especially considering that the cost of alternating pressure mattresses is far higher than high specification foam mattresses or overlays (Nixon et al., 2006). However, once again there is an absence of definitive evidence, and a high quality trial is needed to address this gap in escalation strategies. An effective and apparently simple alternative escalation strategy is to increase the frequency of turning, which is effective in reducing pressure ulcer incidence (Defloor et al., 2005). However, the resource associated with turning may pose a barrier to its effective use. On a 25 bed general hospital ward, 18 patients would likely be ‘at risk’, ‘high risk’ or ‘very high risk’ using the Waterlow score (Clark et al., 2002), which would result in 216 turns per day on a two hourly turning regimen. Data is very limited, but assuming a range of 10–15min per turn (Hibbert et al., 1999, Jaichandar et al., 2007), turning could require 36–54 nursing hours per day per ward if the Waterlow score was used to trigger escalation. The resource required to maintain such regimens may well be beyond the staffing capacity of wards.

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4. Where to from here? 

This brief overview of the evidence base makes it clear that nursing should not uncritically assume that pressure ulcer prevention is a measure of the quality of care or that nursing quality can be easily determined by examining the specific preventative care used. Although there is probably sufficient evidence to give some confidence that actions and decisions typically within nurses’ sphere of responsibility are likely to make a difference, there is not enough evidence to be prescriptive about what precisely should be done under what circumstances.

Firstly there is a paucity of cost effectiveness information, which would help to determine the best way to deploy limited financial and human resources to maximise effect. Secondly, there is a clear need for better assessment tools that accurately predict risk in order to prevent overtreatment since none of the existing ones seem adequate. Ideally, data from an inception cohort without risk reduction strategies is required to avoid the confounding effect of such strategies on predictive accuracy. Use of these tools then need to be evaluated in randomised trials against more declarative strategies, such as awaiting the development of NBE before initiating prevention strategies. However, the drive for quality measurement may diminish the likelihood that accurate tools can be developed, unless thoughtful research designs that strategically address the broad evidence gaps are funded. For instance, future trials testing existing risk assessment tools against a declarative strategy could also use the declarative arm as a validation cohort to develop better risk assessment tools. Thirdly, there is an urgent need to address the effectiveness of high specification foam mattresses in comparison to alternating pressure mattresses. If the cheaper alternative is as effective, such evidence could deliver welcome cost relief for health providers.

In our view, the incidence of pressure ulcers may well be a valid nurse sensitive outcome, albeit one where the amount of variation attributable to nursing is unclear. There is potential to use it as a quality indicator but work still needs to be done. Simple reporting of rates against a denominator will not allow meaningful comparison or benchmarking. Priorities for further research here include the development of a parsimonious risk adjustment model that will allow the comparison of different provider units with different patient case mix (Griffiths et al., 2008).

However, there is no clear basis for identifying any particular care processes, for example the use of risk assessment tools, as indicators of quality. Certainly it would be wrong to effectively impose particular processes and judge the quality of nursing care through nationally collected and reported process indicators. Assessment in itself does not result in better outcomes and there is scant evidence that outcomes are improved by the use of a tool even when risk as assessed by a tool is linked to intervention. Further, the specific interventions that should result from an assessment of risk (with or without the use of a tool) are unclear. While there is some evidence to guide practice it would be wrong to imply certainty of outcomes by selecting care processes as indicators of quality. There is much work still to be done.

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Conflict of interest 

None.

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References 

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PII: S0020-7489(09)00411-8

doi:10.1016/j.ijnurstu.2009.12.019

International Journal of Nursing Studies
Volume 47, Issue 5 , Pages 531-533, May 2010

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