Alternating pressure mattresses to prevent pressure ulceration in patients admitted to hospital are associated with lower costs and greater benefits and are more likely to be cost saving than alternating pressure overlays.
In this study we defined costs as mattress costs and hospital costs. During the trial we observed that grade 2 pressure ulcers did not usually receive dressings and other nursing care therefore we did not estimate for further treatment costs.7
The health benefits associated with the interventions were captured as pressure ulcer free days. We chose this approach rather than the more usual method of trying to capture a patient's utility through changes in quality of life because concurrent illness would dominate any quality of life measurement. Furthermore, the emphasis of our study was on prevention and participants who developed new ulcers were not followed-up until the ulcer healed. Although we did follow the healing of ulcers present at baseline, we did not have quality of life data that related to the time of ulceration (before admission) and therefore could not examine how quality of life changes with the status of pressure ulcers. The effect of pressure ulcer healing on people's health related quality of life may be the subject of future studies.
That the mattress is likely to be economically dominant may initially seem counterintuitive. The mattress has a higher purchase cost and no statistically significant effect on the proportion of patients developing an ulcer, the time to ulceration, the severity of ulcers, or length of stay. However, the purchase cost of these pressure relieving surfaces is low when viewed over their life span, and the difference in costs between overlays and mattresses is small over this time period. For a two year life span, the average cost per day would be £1.38 for an overlay and £5.71 for a mattress (). This cost difference is small in the context of the daily inpatient treatment costs of £165-£385 (depending on specialty) and the reduced length of stay (on average, 1.22 of a day less) for mattress recipients in this trial and translates into an average reduction in costs of £283.6 per patient. The health benefit associated with the interventions was measured as the difference in mean time to develop a pressure ulcer, and also favoured the mattress (on average by 10.64 days). The accompanying clinical paper for this trial reports the median (rather than mean) time to ulceration, as is common practice owing to the skewed distribution of time to event data.6
By contrast, and as recommended for economic analyses, we use the mean time to pressure ulceration since the median would greatly underestimate the costs.8,9
The delay in ulceration associated with alternating pressure mattresses is crucial because the longer a patient avoids ulceration the less likely they are to go on to develop a pressure ulcer; a delay in ulceration allows the patient time to recover sufficiently from their acute episode so that their risk of ulceration recedes. We argue that although time to ulceration was a secondary end point in this trial, it should be considered as a primary end point in future studies since it is more informative economically and clinically. Furthermore, many of the risk factors for pressure ulceration in the participants do not completely disappear on discharge from an acute hospital (for example, impaired mobility), and simple proportions of pressure ulcers developed ignore the censored nature of these data.
Total cost is a function of length of hospital stay which itself is mainly a function of overall health status. Patients who are more ill are both more at risk of pressure ulcers15
and likely to have longer lengths of stay. It is probable that good nursing care, such as the provision of a support surface, will completely prevent pressure ulcers in a proportion of patients and will merely delay the appearance of ulcers in others. If the appearance of an ulcer is a proxy for acuity, and more acutely ill patients consume more healthcare resources, then delays in pressure ulceration suggest a potentially lower consumption of healthcare resources. The longer length of stay in patients with pressure ulcers is probably a consequence of comorbidities rather than the pressure ulcer itself. We found no effect when we tested to see whether the surfaces had a differential effect on length of stay depending on the presence of a pressure ulcer; overall lengths of stay for patients who developed a pressure ulcer on either surface were similar.
Since there are no robust estimates of the cost of a pressure ulcer we were not able to estimate the savings from pressure ulcers prevented. Such a costing study would need to be large, with a considerable length of follow-up, carried out in several centres to ensure generalisability, and would require careful observation of clinical practice in nursing care. It was not possible to undertake such a costing study within this trial.
Our results oppose those from the model based cost effectiveness analysis by Fleurence because data in that trial were based on expert opinion whereas we collected data within the trial.16
Furthermore, the previous model disregarded the fact that pressure ulcers are rarely the main reason for people being admitted to hospital. Thus the marginal cost of treating a pressure ulcer in hospital may be small compared with the overall costs of hospital treatment. In this sense our analysis reflects actual practice. Our assumption that participants remained on the allocated pressure relieving surface over their entire hospital stay is a conservative one; in reality patients are moved on to standard mattresses or higher specification surfaces after major changes in their risk of pressure ulcers. Given participants in the overlay group developed pressure ulcers earlier than those on the mattresses, this assumption will have over-estimated the cost of the mattresses, thus strengthening our conclusions.
Although neither the difference in mean overall hospital costs nor the difference in mean time to development of pressure ulcers between the two surfaces were statistically significant, decision makers need to make a decision. Failing to do so until statistically significant evidence becomes available would deny patients the possibility of experiencing the expected health benefits at an earlier stage and prevent the realisation of expected savings to the NHS.9
Although there was considerable uncertainty around the point estimates of mean health benefits and costs shown in , this should not result in large decision uncertainty for decision makers since even for large willingness to pay values () the probability of the overlays being cost effective is only between 10% and 20%.17
What is already known on this topic
No previous trial based economic evaluation has compared alternating pressure mattresses with the less costly alternating pressure overlays
What this study adds
Alternating pressure mattresses were associated with lower costs and greater benefits and are more likely to be cost saving than alternating pressure overlays