5 Cost considerations
5.1 The company did a literature search and identified 5 studies that met their selection criteria. All studies used cost–benefit analyses. Of these, 3 studies were done in the USA (Veenstra et al. 1999; Crawford et al. 2004 and Ye et al. 2011), 1 study was done in the UK (Hockenhull et al. 2008) and 1 study was done in France (Schwebel et al. 2012). In 2 of the studies, the comparison was between an antiseptic‑impregnated catheter and a standard catheter (Veenstra et al. 1999 and Hockenhull et al. 2008). In the remaining 3 studies (Crawford et al. 2004; Schwebel et al. 2012 and Ye et al. 2011), the intervention was a chlorhexidine gluconate (CHG)‑impregnated dressing and the comparator was a standard dressing. None of the included studies involved the 3M Tegaderm CHG IV securement dressing (Tegaderm CHG).
5.2 The External Assessment Centre considered none of the company's identified studies to be relevant because they did not compare Tegaderm CHG with either of the comparators. It did additional searches and identified 4 economic studies; all used cost–benefit analyses and compared Tegaderm CHG with a standard dressing (Maunoury et al. 2013, 2014 and Palka‑Santini et al. 2014a, 2014b). All were published as conference abstracts after the company's searches. All the studies were carried out from the perspective of the health service in France, were written by the same authors, and used data from Timsit et al. (2012). Each study used different model structures or reported different results, all involved a non‑homogeneous Markov model, and were concerned with various measures of infection. No statistically significant differences in costs were reported between the dressings. The External Assessment Centre was unable to assess the relevance of these data to the NHS given the limited information provided.
5.3 The company presented a cost analysis comparing Tegaderm CHG against a standard dressing (Tegaderm IV 1635). The costs of another commonly used, but more expensive, standard dressing (Opsite IV 3000, Smith and Nephew) were also quoted, but not used in the model. The company did not include the CHG‑impregnated sponge dressing in the model because of the lack of direct comparative clinical evidence. The economic model presented by the company was a decision tree with a short time horizon that included the catheterisation period and any additional length of stay associated with catheter‑related bloodstream infections (CRBSI). The model used an NHS perspective. The decision tree simulated intensive care unit patients who had an absolute risk of getting CRBSI, local site infection or dermatitis. Each outcome was a separate health state and the model captured the number of patients in each state and the cost of being in that state (dressings and management costs).
5.4 Each time the model was run, Monte Carlo simulation was used to select values at random from the pre‑specified distributions associated with each of the input parameters, apart from the unit cost of the dressings. This approach allowed the effects of the joint uncertainty across the parameters of the model to be considered. The company's base‑case results were probabilistic, based on 1,000 iterations of the model.
5.5 The External Assessment Centre considered that the structure of the model was appropriate, capturing the main differences in reported clinical outcomes and cost differences between Tegaderm CHG and standard dressings. However, it noted that the model diagram did not include in its end states patients who had no complications, and amended the model diagram to include this state. The company did not report any structural assumptions in the model. However, the External Assessment Centre identified the following:
There was no difference in outcomes beyond the short time horizon of the study.
The length of time a patient has a catheter was not influenced by whether or not they had an infection (CRBSI or local).
The risk of having any of the study outcomes was mutually exclusive and independent.
The dressings only affected actual outcomes and not suspected outcomes, which would also incur costs of investigation.
Infection rates were assumed to be linear regardless of catheter dwell time.
There were no practical differences in dressing management between the dressings such as time to apply and remove, wastage and training.
5.6 The External Assessment Centre judged that these simplifying assumptions were unlikely to influence the results of the company's model significantly.
5.7 The company used data from Timsit et al. (2012) to populate the parameters for all the clinical end points in the model. The model's time horizon of 10 days was based on the mean duration of catheterisation for critically ill patients reported in the study by Ye et al. (2012). Patients who had a CRBSI incurred an additional length of stay of 3 days in an intensive care unit and 7 days in a ward, with resource use costs based on figures reported in the Hockenhull et al. (2008) study. Baseline rates or risks for the clinical end points were obtained from a number of sources. The rate for CRBSI (1.48 per 1,000 catheter days) was taken from Bion et al. (2012), based on 2010 final quarter figures from the Matching Michigan study; for local site infection (0.1 per patient) from Ye et al. (2011); and risk for dermatitis (0.0026 per catheter) from Schwebel et al. (2012).
5.8 The costs for the Tegaderm CHG and the standard dressing (Tegaderm IV 1635) used in the company's model were based on the cost of the most commonly‑used size of dressing, and were £6.21 and £1.34 respectively. These figures were provided by the company.
5.9 The cost for a CRBSI of £9,900 was based on the figure reported in the health technology assessment paper by Hockenhull et al. (2010), inflated to 2012/13 prices. This value was used in NICE's guideline on healthcare-associated infections. The company produced its own cost estimate for CRBSI based on resource use identified through expert advice, which agreed with this £9,900 figure. The cost of dermatitis of £150 used in the company's model was based on the cost of 4 standard dressings, removing the existing catheter, and replacing it with a new catheter. Local site infections were given a cost of £250 based on the US $400 figure reported in the study by Saint et al. (2000).
5.10 The company's base‑case results reported an average cost of £99.63 per patient for the Tegaderm CHG dressing compared with £176.89 per patient for the standard dressing. This would give an average saving of £77.26 per patient if Tegaderm CHG were adopted. The probability of Tegaderm CHG being cost saving over standard dressings was calculated at 98.5%. The key driver of this cost saving was avoiding CRBSI through using Tegaderm CHG.
5.11 The company presented univariate deterministic analysis on both the cost of CRBSI and its baseline rate to explore how robust the estimated cost savings of Tegaderm CHG compared with standard dressings were to changes in these key variables. If a low estimate of CRBSI rate of 0.5 per 1,000 catheter days was used the cost savings with Tegaderm CHG were £23 per patient; if a high estimate of 5.5 per 1,000 catheter days was used the savings with Tegaderm CHG increased to £135 per patient. Based on a low estimate of £5,000 for treating a CRBSI and a high estimate of £15,000, Tegaderm CHG generated cost savings per patient of £36 and £119 respectively.
5.12 The External Assessment Centre reviewed the parameters and costs used in the company's model. It contacted clinical experts who validated the company's estimated resource use associated with CRBSI.
5.13 The External Assessment Centre revised the company's value for baseline local site infection rate to 0.14 per 1,000 catheter days based on 2013 audited rates for NHS Wales published by the Welsh Healthcare Associated Infection Programme (2014).
5.14 The External Assessment Centre judged it more appropriate to use the probability of 1 case of dermatitis per 476 patients reported in the Timsit et al. (2012) study. The External Assessment Centre revised the relative risk of dermatitis to 1, based on commercial‑in‑confidence global event data provided by the company on the reduced rate of dermatitis after design improvements in the breathability of the Tegaderm CHG dressing.
5.15 The External Assessment Centre calculated a weighted average cost for the dressings, taken from the NHS Supply Chain costs. For Tegaderm CHG the cost was based on the proportionate sales figures for the 4 dressing sizes and was estimated as £6.26 per dressing. The cost of the standard dressing was based on the proportionate sales figures of 2 commonly‑used standard dressings, Tegaderm IV and Opsite IV 3000, and was estimated as £1.54 per dressing. The External Assessment Centre estimated the cost of a CHG‑impregnated dressing to be £8.13.
5.16 The External Assessment Centre was advised by experts that it was not usual procedure to remove the catheter if a patient developed dermatitis. It therefore considered that the company's costs of the consequences of dermatitis overestimated the true cost. The External Assessment Centre therefore estimated a lower value, which involved the costs of dressings only, but assumed, as did the company, that patients with dermatitis would need more frequent dressing changes. It assumed the use of 1 additional dressing. Therefore the cost of dermatitis was revised to £6.
5.17 The study by Saint et al. (2000), which provided the cost for local site infection used in the company's model, provided no details on how that cost was generated. The External Assessment Centre therefore sought expert advice to derive its own cost estimate, £100, which was lower than that used in the company's model.
5.18 The External Assessment Centre also sought expert advice on the number of dressings used. This agreed with the company's estimate of 3 dressings over a 10‑day catheterisation period.
5.19 The External Assessment Centre identified 2 main weaknesses in the company's economic analysis. First, there was no rationale for the choice of distributions and coefficients used in the probabilistic sensitivity analysis done by the company. However, the External Assessment Centre noted that this was not needed as part of the submission template. Second, the company did not attempt to make any judgement on the comparative cost effectiveness of Tegaderm CHG and a CHG‑impregnated sponge dressing. The External Assessment Centre addressed both these concerns in the assessment report.
5.20 The External Assessment Centre re‑ran the company's model with their revisions to the parameter values and distributions. It also ran an additional scenario in which the baseline CRBSI rate for England was substituted with that reported for Scotland in 2013 of 0.3 per 1,000 catheter days. Both deterministic and probabilistic sensitivity analyses were done. The External Assessment Centre's deterministic base‑case results using CRBSI data from England produced an average per patient cost of £77.75 for Tegaderm CHG and £151.29 for a standard dressing, a cost saving of £73.54. When CRBSI data from Scotland were used, Tegaderm CHG had an average per patient cost of £30.79 and a standard dressing cost of £34.47; a cost saving of £3.68 per patient. The External Assessment Centre varied the baseline CRBSI rate and identified the threshold at which Tegaderm CHG was cost neutral as 0.24 per 1,000 catheter days.
5.21 The External Assessment Centre ran both univariate and multivariate probabilistic sensitivity analyses, varying the model parameters using their ranges and distributions. In the probabilistic sensitivity analysis varying all the model parameters, Tegaderm CHG had a 97.8% probability of being cost saving using the baseline CRBSI rate for England, but this fell to 57.9% when the figure for Scotland was used.
5.22 The External Assessment Centre also presented an exploratory cost analysis of Tegaderm CHG compared with CHG‑impregnated sponge dressings. There were no comparative data and from the limited evidence available (including similar data on adverse events), the External Assessment Centre concluded that it was plausible to assume that the 2 dressings had similar safety and efficacy. Without hard data on outcomes this exploratory work relied on observational studies and expert opinion. This suggested that resource use was similar between the 2 dressings, with any cost differences relying on acquisition cost. Based on NHS Supply Chain costs for Biopatch and the cheapest standard dressing (Tegaderm IV) the cost for a CHG‑impregnated sponge dressing was calculated at £8.13, compared with £6.26 for Tegaderm CHG. No sales data were available through the NHS Supply Chain. Expert opinion indicated that NHS trusts would probably purchase through other sources at a lower price than the NHS Supply Chain listed price. Therefore the External Assessment Centre calculated additional costings using the price provided by 3M for Biopatch, of £5.16 per dressing. This resulted in a total price of £6.49, slightly more expensive than Tegaderm CHG.
5.23 The Committee noted the cost modelling presented by the company and the adjustments made by the External Assessment Centre. It considered that the revisions made by the External Assessment Centre were plausible. The Committee considered that the External Assessment Centre's sensitivity analyses addressed the uncertainties in the economic model. It concluded that the estimated cost savings for Tegaderm CHG compared with standard semipermeable transparent dressings were likely to be realised in practice, with actual savings dependent on the baseline CRBSI rate.
5.24 The Committee considered that the baseline CRBSI rate was a key driver of the savings in the cost model. It noted that Tegaderm CHG was cost neutral when the baseline CRBSI rate was 0.24 per 1,000 catheter days and became cost incurring when the baseline rate fell below that figure. The Committee heard expert opinion that CRBSI rates in England have been falling in recent years. It heard from both the External Assessment Centre and the experts that there are differences in the definition and measurement of CRBSI between different countries and different hospitals, which makes comparison of infection rates difficult. The Committee concluded that Tegaderm CHG is likely to be cost saving in hospitals where the baseline CRBSI rate is above about 0.24 per 1,000 catheter days. It also concluded that Tegaderm CHG could potentially provide a useful way of reducing infection rates further in those hospitals that have not managed to do this by other means.
5.25 For the guidance review, the External Assessment Centre revised the model to reflect 2019 costs. The main parameter changes were (original guidance values given in brackets):
baseline incidence rate of CRBSI for Scottish intensive care units: 0.28 per 1000 catheter days (0.3 per 1,000 catheter days)
baseline incidence rate of local site infection: 0.4 per 1,000 catheter days (0.14 per 1,000 catheter days)
baseline incidence rate of dermatitis: 0.3 per 1,000 catheter days (0.002 1‑year probability)
the effectiveness of Tegaderm CHG for preventing CRBSI: 0.402 hazard ratio (0.45 relative risk)
length of stay with catheterisation: 13 days (10 days).
The cost of Tegaderm CHG was also updated to reflect the 2% decrease in the cost of the dressing (from £6.21 to £6.09). The External Assessment Centre assumed this reduction was implemented in all sizes of Tegaderm CHG and estimated an updated weighted average of £6.14 (£6.26), using the sales proportions from the original cost model. Other costs from the original model were adjusted for inflation. Deterministic base‑case results for the 2019 revised model produced an average per patient cost of £106.62 (£77.75) for Tegaderm CHG and £199.69 (£151.29) for a standard dressing, a cost saving of £93.07 (£73.54) when considering a baseline CRBSI rate of 1.48 per 1,000 catheter days. When CRBSI data from Scotland were used, Tegaderm CHG had an average per patient cost of £35.80 (£30.79) and a standard dressing cost of £43.30 (£34.47): a cost saving of £7.50 (£3.68) per patient. In the probabilistic sensitivity analysis, Tegaderm CHG had a 98.9% (97.8%) probability of being cost saving using the baseline CRBSI rate for England, but this fell to 50.3% (57.9%) when the figure for Scotland was used. The External Assessment Centre varied the baseline CRBSI rate and identified the threshold at which Tegaderm CHG was cost neutral as 0.18 (0.24) per 1,000 catheter days. Further details of the 2019 revised model are in the cost model update report.