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Cost analysis of Topical Negative Pressure (TNP) Therapy for traumatic acquired wounds

Extended traumatic wounds require extended reconstructive operations and are accompanied by long hospitalizations and risks of infection, thrombosis and flap loss. In particular, the frequently used Topical Negative Pressure (TNP) Therapy is regarded as cost-intensive. The costs of TNP in the context of traumatic wounds is analyzed using the method of health economic evaluation. All patients (n=67: 45 male, 22 female; average age 54 y) with traumatically acquired wounds being treated with TNP at the university hospital of Goettingen in the period 01/01/2005–31/12/2007 comprise the basis for this analysis. The concept of activity-based costing based on clinical pathways according to InEK (National Institute for the Hospital Remuneration System) systematic calculations was chosen for cost accounting. In addition, a special module system adaptable for individual courses of disease was developed. The treated wounds were located on a lower extremity in 83.7% of cases (n=56) and on an upper extremity in 16.3% of cases (n=11). The average time of hospitalization of the patients was 54 days. Twenty-five patients (37.31%) exceeded the „maximum length of stay“ of their associated DRG (Diagnosis Related Groups). The total PCCL (patient clinical complexity level = patient severity score) of 2.99 reflects the seriousness of disease. For the treatment of the 67 patients, total costs were $1,729,922.32 (1,249,176.91 €). The cost calculation showed a financial deficit of $–210,932.50 (–152,314.36 €). Within the entire treatment costs of $218,848.07 (158,030.19 €), 12.65% per case were created by TNP with material costs of $102,528.74 (74,036 €), representing 5.92% of entire costs. The cost of TNP per patient averaged $3,266.39 (2,358.66 €). The main portion of the costs was not – as is often expected – due to high material costs of TNP but instead to long-term treatments. Because of their complexity, the cases are insufficiently represented in the lump-sum calculation of the InEK. A differentiated integration of complex TNP-treatment in the DRG system (e.g., as an expanded DRG I98Z) would be a step towards cost recovery. In addition, the refunding of outpatient TNP-treatment would lead to enhanced quality of life for the patients and to a reduction of hospital costs and length of stay.


Introduction
Large traumatic wounds are frequent and cost-intensive problems in the treatment of severely injured patients. They require extended reconstructive operations and are accompanied by long hospitalizations and risks of infection, thrombosis and flap-loss [1]. The topical negative pressure (TNP) therapy provides a paradigm that can be used in concert with a wide variety of standard existing plastic surgery techniques [2]. It is one of the essential methods in treatment of these wounds and has become an integral part of the clinical routine [3]. Fleischmann et al. [4] were the first to describe the treatment of acute soft tissue trauma (primarily combined with open fractures) with TNP. There is a need for more economic analysis research in plastic surgery studies [5]. The cost-effectiveness of TNP has been evaluated in four large studies in the USA [6], [7], [8] and the Netherlands [9], but all of them evaluated chronic wounds. Until now, no economic evaluations of treatment of traumatic wounds with TNP exist. Nord et al. [10] describe TNP as one of the most cost-effective methods for wound treatment. The high material costs of TNP may be balanced by reduced nursing-costs and reduced hospitalization-time for the patients [11]. The morbidity and mortality after postoperative infections of the sternum is reduced with TNP [12]. Since 2004 coding of TNP in the German DRG accounting system is possible with the new OPS (German Procedure Classification)-Code 5-916.a [13]. To reflect the complexity of TNP especially in the treatment of musculoskeletal trauma the DRG I98Z was established in 2007. Until now, it has been unclear whether the existing proceeding calculation of the InEK (National Institute for the Hospital Remuneration System) covers the actual costs of TNP for traumatic wounds. Economic evaluation is a way of assessing medical procedures [14]. The aim is to obtain objective information allowing for a transparent estimation of costs associated with a medical measure [15]. This process facilitates decisions about allocation of resources, regulation or development processes [16]. Dependent on the perspective, different study profiles can be used: non-comparativestudies (like "cost-analysis" or "disease-cost-analysis") or comparative studies like "cost-benefit-analysis" or "cost-effective-analysis" [14]. The approval used in eval- uation studies is defined by the "Hannoveraner Konsens" [15]. In our study, we used the "cost-analysis" study profile measuring the concrete costs of a procedure as activity-based costing based on clinical pathways [14]. The following questions form the basis of this evaluation ( Figure 1 Activity-based costing allocates the individual-and overhead-costs to processes. All treatment activities were described and evaluated in process-modules (e.g., ward rounds, blood collection, documentation). Modules belonging together were combined to process-blocks (e.g. emergency room, operation, ward) ( Table 1). The processblocks together represent the overall process. Due to the heterogeneity of cases, the sequence of the processblocks was adapted individually to each patient. The combination of the process-blocks in relation to the individual patient carriers (dependent on length of hospitalization, amount of operations or complications) represents the clinical pathway. Non-patient-related overall costs (personnel and material costs of medical and nonmedical infrastructure) were not represented; they were allocated using percentages as overhead costs for each case. The clinical pathway allowed the identification of real costs arising from TNP. The cost categories were chosen according to the InEK-calculation-compendium to rise comparability of measurement [17].
The physician-related activity was calculated with workingminutes for every process-modules and -blocks ( Table 2). For the process-block "operation" the working-minutes Table 2: Calculation physician-related activity (ward and OP) The costs of physician-related activity on the ward are calculated by multiplication of occurred process blocks during therapy with cost/working minute. For calculating costs of the operations, working minutes of surgeons (incl. bedding of patients, documentation time) and anesthesists (considering premedication, recovery room) are combined. Origin: own construction. Table 3: Nursing-related activity; the LEP-variable groups The nursing-related activity was collected by the LEP (detection of nursing activity) system. It is based on the daily documentation of patient-related care variables and nursing efforts in a special software program. Origin: own construction.
were not standardized due to the individuality of the activity. Therefore, the summarized "surgeon-presencetime"/"cut-to-suture time"/"anesthesia-time" and the blocks "pre-medication"/"post-op-recovery-room-time" was calculated ( Table 2). The nursing-related activity was collected by the LEP (detection of nursing activity) system. It is based on daily documentation of patient-related care variables and nursing efforts in a special software program ( Table 3).
The activity of other functions and medical-technical service (physiotherapists, patient transport service) were included into overhead costs. The material costs were calculated separately; costs of pharmaceuticals and general medical treatment were calculated according to the InEK calculation-system: overall costs were divided by the LEP-hours to obtain a cost rate per LEP-hour. The costs of the implants (osteosynthesis material) were individually attached to patients from the OP-information system and costs were generated from purchasing department. Material costs of the TNP-system were calculated by multiplication of the day rate of TNP-therapy (66.40 €/d for providing of the pump system and the dressing materials) with the length of treatment. After calculation of cost categories, they were assigned to their particular cost unit (e.g. ward, anesthesia, radiology) according to the InEK calculation-system.  (Table 4, last column, Table  5).
In addition, costs were referred and analyzed according to the DRG earnings. The DRG-system of the year 2007 was used. All cases of 2005 and 2006 were newly grouped using the 2007 system because the DRG I98Z (complex negative pressure therapy of diseases and disruption of musculoskeletal system and connective tissue) was not established prior to 2007. To confirm robustness of data a sensitivity-analysis was performed. Judgmental parameters were varied to represent the heterogeneity of the cases. In a "best-case" and "worst-case" analysis the parameters "base-case-value" for the funding agency and "pathway-minutes" for the supplier were reviewed in order to determine their sensitivity.
A summary of the calculation system is given in Table 4. The study was certified by our institutional ethics committee (AZ 13/3/08).

Results
In No patient was released from the hospital prior to the "lowest residence time", and 28.36% (n=19) were released before reaching the "middle residence time". The evaluated cases had a PCCL (describes a patient severity score in four steps from undemanding (PCCL 0) to complex, severe (PCCL 4) diseases and treatments) of 2.99, reflecting the complex and severe nature of the cases.
To answer the questions posed in the introduction (Figure 1), the following results can be presented (question 3 will be answered in the Discussion):  (Table 6). Table 5 presents the calculation of overhead costs related to the different length of hospital stay.
Performing the sensitivity analysis from the perspective of the funding agency with varying "base-case-values", an overall cost of 993,114.2 € arises for the "best-casescenario" of TNP treated traumatic tissue defects. In calculating "worst-case-scenario", the overall costs are 1,096,698. 23 €. Thus, costs for the funding agency vary by an absolute 106,177.99 €. The sensitivity analysis from the point of view of the supplier depends on diverging "pathway-minutes". The variation intervals for the pathway-minutes were calculated using a variation coefficient. For the supplier (hospital) the overall costs can be reduced by 87,829.83 € total or 1,310.89 € per case for the "best-case-scenario". For the "worst-case-scenario" the overall costs increase by about 81,330.59 € total/1,213.89 € per case.   Table 7. (CC=cost categories, P1-3 = patients with primary tissue defects, S1-3 = patients with secondary tissue defects). Origin: own construction.
Thus, the funding situation for the hospital even in the "best-case-scenario" is not covering the cost of treatment. The loss amounts for the best-case-scenario to 962.46 € per case and to 3.490.45 € per case for the worst-scenario.
The DRG-related cost analysis is presented in Table 7; in Table 8 the cost-revenue ratio is shown and Table 6 presents the summarized results of the cost analysis.

Discussion
In trauma patients, primary and secondary tissue defects often require long duration of treatment. For therapy of these traumatic wounds, TNP-therapy represents an essential and frequently used technique [3]. The high cost of medical care has come under scrutiny by payers and physicians [18] and since the introduction of the DRG I98Z in 2007 it remains unclear whether treatment with TNP for traumatic wounds can be done in a cost-covering fashion.
For the patient collective of this study all trauma patients were chosen for which TNP therapy presents, next to their osteosynthesis, a main part of their therapy. Patients grouped in a "multiple trauma DRG" and "artificial respiration DRG" were not included in the study, because TNP therapy and its costs play only a minor role and reimbursement of such cases is calculated differently. In addition, patients with chronical defects were also excluded due to their high number of concomitant diseases. We are aware that the DRG system does not allow for total cost coverage for every DRG. However, the negative cost-revenue ratio of -18.86% in cases of primary defects can hardly be compensated by DRGs with a positive ratio.
3. Based on these results, some strategic consequences can be considered. First, structural changes were performed to ensure the efficiency: material resources were concentrated on few storerooms to reduce the part of material notused and out of date. Thus, costs have already been reduced by about 90,000 € in 2007. Due to new contracts on the part of the procurement department in 2006, another 15% of material costs could have been saved. *The assumed high material costs in the context of treatment with TNP often present the decision criterion for the supplier. However, the presented analysis showed that material costs of TNP were only a relatively small portion, making up 5.93% of total costs. A savings opportunity should be to implement a standardized approach for treatment with TNP. Trueman et al. [11] already showed a significant reduction in hospitalization time with a standardization of TNP-therapy. But until now, there exist no standardized guidelines for the use of TNP therapy [4], [19]. Another opportunity could be the optimization of coding procedures, but due to the presence of a controlling specialist there are no deficits in this aspect in our clinic.   From the economic point of view an adaptation of the product-portfolio of the corporation (hospital) would be an important step to remain capable of acting and competing. However, for a tertiary care hospital of maximal treatment such adaptations are not possible because it has to provide all diagnostic and therapeutic possibilities. In addition, the number of complex medical cases with severe diseases in a university hospital is elevated, which reduces the possibilities of cost-optimization and benchmarking [20]. A large amount of the evaluated cases is not represented by calculation of case-based lump sum of the InEK. The reason could be the activity profile of the 249 participating hospitals. A strategy for improvement would be the participation of many tertiary care hospitals in calculations of the InEK. Furthermore, complex cases could be represented in an appropriate manner in the DRG system. As an important consideration, the DRG system has to develop continuously and learn to sustain the rising costs. After introduction of the DRG I98Z in 2007 in the DRG system, an adaptation and differentiation of this DRG is necessary. Besides the complex TNPtherapy, the new DRG should include patients with primary tissue defects needing complex procedures. Tissue defects cause in case of long-term therapy extensive costs for the health insurance companies. Thus, the discussion about refunding of outpatient TNP-therapy has been going on for years. In cases where it is possible from the medical point of view, outpatient therapy would lead to enhanced quality of life for the patients and to a reduction of hospital costs and lengths of hospitalization. However in other countries (USA, Great Britain, Austria and Switzerland) outpatient TNP-therapy is already an established practice [21], the IQWIG (Institute for Quality and Efficiency in Health Care, Germany) refused the absorption of outpatient TNP therapy costs due to insufficient existing research data concerning this topic [22]. The accomplishment of prospective randomized studies would likely change the cost-refunding situation for outpatient TNP-therapy.
The presented work focused on the presentation of the developed method of gaining a cost analysis, as well as on the analysis of the real arising costs of TNP therapy of traumatic wounds. Therefore, we did not analyze the surgical treatment itself. However, evaluating the number of operations in the total collective, there were average 5.9 operations necessary per case (Table 7). This has to be related to the high PCCL-level of 2.99, indicating the severe injuries of our patients. With mostly 1-2 operations for the osteosynthesis and one operation for the final wound closure, there remain average 3-4 operations for changing TNP dressings. Often, not only the wound situation requires a conditioning about several TNP steps, but also the general situation of the patient is critical (high PCCL) and does not allow extended flap surgery in an early step. The department for Trauma Surgery, Plastic and Reconstructive Surgery, University Hospital of Goettingen, as Level-A Hospital, performes their therapies according to the current actual treatment guidelines of the representative associations (DGOU and DGPRÄC, German Association of Orthopaedic and Trauma Surgery, German Association of Plastic, Reconstructive and Aesthetic Surgery) . So it can be assumed, that there are no treatments performed, which would expand the arising costs or distort or the representativeness of the evaluated results. However, the suppliers have to revise carefully the undergone therapies. Even if the treatments were done according to established standards and guidelines, there might be in some cases an opportunity to close the large tissue defects earlier by plastic-reconstructive methods. This could reduce the length of stay of the patients and therewith the main cost fraction of this treatment collective. The use of standardized accounting can be a strategically effective method [23]. With the use of a disease-costing analysis a tool of economic evaluation has been applied to analyze costs of a special therapy. Within activity-based costing, modules for establishment of clinical pathways were developed. On this basis, further therapies of other diseases can be analyzed for their cost-revenue ratios. An enhanced degree of cost-transparency can now be reached and realization of further analyses will be simplified.

Conflicts of interest
None of the authors has a commercial association or financial interest in any of the products, devices, or drugs mentioned in this article that might constitute a conflict of interest.