The MIST Therapy system for the promotion of wound healing

The economic evidence for the MIST Therapy system comprised an unpublished cost-effectiveness study, a conference poster and a new cost analysis.

An unpublished study from the USA considered the economic impact of healing a foot ulcer in a patient with diabetes using the MIST Therapy system plus standard wound care compared with standard wound care alone (Driver 2010). The effectiveness of the 2 treatments was taken from peer-reviewed studies about foot ulcers in patients with diabetes and the primary outcome measure was defined as 'time to heal'. The study estimated that for every 1,000 patients treated for a 12-week period, the cost savings were US $2,555,620. The savings associated with the MIST Therapy system resulted from the greater proportion of ulcers that healed or progressed towards healing within 12 weeks. The assumed difference in healing rate between the 2 treatments was large, and it was not clear how the costs attributed to each treatment were derived.

The conference poster described an economic evaluation based on a case series of 5 patients with pressure ulcers treated using the MIST Therapy system and standard wound care for 2 months (Anaeme et al. 2009). Cost savings were estimated from the direct costs of using the MIST Therapy system compared with negative pressure wound therapy as an adjunct to standard care. The cost calculations of negative pressure wound therapy were not described. The poster reported that mean wound area decreased by 34% during treatment with the MIST Therapy system. This was claimed to offer an average saving of US $1,310, ranging from $563 to $2,187 per patient compared with the use of negative pressure wound therapy.

The cost model submitted by the manufacturer was based on an estimate of 600,000 leg ulcers, pressure ulcers and diabetic foot ulcers in the UK and an estimate of £2.3 billion to £3.1 billion as the total cost of treating chronic wounds in England and Wales in 2005 (Posnett and Franks 2008). The population-based costs and incidence were used to calculate an annual per-patient cost for each type of ulcer. These costs per patient were compared with the cost of 26 weeks of treatment with the MIST Therapy system.

In the cost analysis, it was assumed that the use of MIST Therapy would follow the current care pathway for the treatment of wounds; it would be used if standard wound care had failed to heal the wound or if the wound had not improved within 30 days. The treatment would take place at the same time as the changing of wound dressings during standard wound care so it was assumed in the cost model that there would be no additional nurse visits. The additional nurse time taken to treat a patient with the MIST Therapy system alongside standard wound care was not analysed in the cost model. This analysis of differences in nurse time could not be undertaken owing to the different approaches used to calculate the cost of treatment with the MIST Therapy system and standard wound care.

For the purposes of the cost analysis, the effectiveness of the MIST Therapy system was described as mean time to healing. This was calculated as 14 weeks from a number of studies with different study design. In the cost model, a mean healing time of 26 weeks for the MIST Therapy system was assumed compared with 52 weeks for continual standard wound care.

The costs associated with treatment included annual rental of the MIST Therapy system, administration of the therapy, MIST Therapy consumables and dressings for standard wound care. The cost of ordering, transporting, processing and storing consumables was not included in the analysis. The energy cost and the cost of disposal of consumables was also not included in the analysis.

The annual total rental cost of the MIST Therapy system is £7,500.

The treatment cost for the MIST Therapy system is £7,626 per patient for 26 weeks based on 3 treatments per week. Rental cost per treatment was estimated to be £6 assuming one MIST Therapy system would be used on 5 patients per day 5 days a week. Its consumables cost was calculated to be £35 per treatment. The treatment cost for MIST Therapy also included wound dressing costs at £7 per treatment and nursing time at £50 per visit.

The costs of standard wound care were calculated from NHS annual wound statistics for complex wounds, and estimated total wound care costs in the UK for each ulcer type, to calculate an average cost per patient ('top down' approach). The costs of the MIST Therapy system were calculated from the estimated resource use per treatment ('bottom up' approach).

The MIST Therapy cost analysis showed that the average cost per patient over 26 weeks of treatment was estimated to be £7,626 for leg, diabetic foot and pressure ulcers. The main cost saving included in the manufacturer's cost analysis related to the reduction in the time for a wound to heal compared with standard wound care alone. The annual cost savings per patient were £1,563, £2,374 and £2,925 for the treatment of leg, diabetic foot and pressure ulcers respectively.

The sensitivity analyses reported that time to heal was the most important factor for the MIST Therapy system to be cost saving to the NHS.

The committee was concerned that the approaches used to calculate the costs of treatment with the MIST Therapy system and with standard wound care were different. The costs of standard wound care were calculated from incidence and population-based costs ('top down' approach) in contrast to the costs of the MIST Therapy system, which were calculated from the annual rental cost of the device, consumables and treatment costs ('bottom up' approach).

The committee discussed the assumption used in the model of a healing time of 26 weeks for the MIST Therapy system compared with 52 weeks for standard wound care. It considered that a 50% reduction in healing time from using the MIST Therapy system was not adequately supported by the clinical evidence.

The committee considered that uncertainty about the conclusions of the cost model were related primarily to uncertainty about the relative clinical effectiveness of the MIST Therapy system in promoting wound healing. This was an important consideration in determining the committee's recommendation for further comparative research.

The committee was advised that exclusion from the cost model of amputation and other procedures with substantial long-term cost implications meant that cost savings of the MIST Therapy system were potentially underestimated.