1. INTRODUCTION
1.2. Organization
Economic evaluation
A CEA is an analytic approach for contrasting the incremental health benefits with the incremental resource expenditures associated with competing health technologies. A cohort simulation model was developed to determine from a payers perspective, the cost effectiveness of three alternative treatment strategies for symptomatic varicose veins. All analysis were conducted using Microsoft Excel 2010 and TreeAge Pro 2010 (TREEAGE software Inc; Williamstown, MA).
Treatment strategy
There were three alternative treatment strategies evaluated:
1. Conventional open surgery using ligation and stripping (Figure E.1) conducted in a hospital outpatient setting. Although there are exceptions, patients that have surgeries conducted in an inpatient hospital setting are generally not suitable candidates for EVLA or RFA. Hence the comparative analysis focuses on conventional open surgery procedures conducted in an outpatient setting as these patients are deemed to be the primary suitable candidates for EVLA or RFA.
2. EVLA (Figure E.2) conducted in a NHSF.
3. RFA (Figure E.2) conducted in a NHSF.
The care pathway shown in Figures E.1 and E.2 were developed in consultation with the expert advisory committee. While it is acknowledged that in actual clinical practice there will be variations to the care pathways shown, the pathways included in this analysis were determined to be a suitable representation for the typical case.
Figure E.1: Clinical pathway and resources used for surgery
Initial Surgery
Post op check at 2 to 6 weeks Ultrasound assessment at 3 months
Yes
o Follow-up physician visit o Doppler ultrasound (for
post-op assessment only)
Time Horizon: 3 years
*: AH data showed that
approximately 13% surgery was conducted in inpatient OR, and other 87% in outpatient OR. In the base case analysis, hospital costs were estimated based on overall patients in inpatient and outpatient OR.
However, the cost based on outpatient was considered in a scenario analysis.
§: Primary failure is failure to completely abolish reflux in the axial vein (refer to Table T.3 for detailed definition).
Figure E.2: Clinical pathway and resources used for EVLA/RFA
Markov model
Figure E.3 shows the cost effectiveness simulation model based on the three alternative treatment strategies. There are three main states in the model including treatment success, failure (requiring major re-intervention) and maintenance therapy. The time horizon adopted for the analysis
considered costs from initial procedure to three years post operation. A time horizon of 3 years was adopted because patients typically do not return with symptoms requiring major retreatment (i.e.
surgery, EVLA or RFA) after 3 years (personal communication, Dr. Ronald St. Germaine,
December 10, 2012 at IHE). Each cycle in the model represents 1 year. Each year, probabilities for treatment outcome, failure and maintenance therapy are applied which dictate how patients flow through the model. Hence based on the characteristics of each treatment strategy a different set of costs and outcomes will be generated forming the basis of the comparative analysis.
Initial EVLA/RFA
Post op check at 2 to 6 weeks Ultrasound assessment at 3 months
Yes
Resources used
Setting:
o NHSF
Resources:
o Facility o Equipment
(Laser/radiofrequency Kit, ultrasound)
o Labour
surgeon
surgical nurse
o Follow-up physician visit o Doppler ultrasound (for
post-op assessment only)
Time Horizon: 3 years
60% receiving foam sclerotherapy
maintenance No
Failure?
Retreatment with EVLA/RFA
Figure E.3: Markov model of a treatment strategy
Model inputs Probabilities
Probability inputs associated with each treatment strategy were obtained from the literature (Table E.1). Inputs for which could not be informed by the literature were derived from the EAG. It is important to note that for the strategies incorporating EVLA or RFA, there was no data to inform the proportion of failures that would be treated with EVLA or RFA and were assumed to be distributed equally in the base analysis.
Table E.1: Clinical and QoL data inputs
Parameter Mean Range Distribution Source
Failure rate of surgery§ 0.033 0.02¶ 0.045 Beta Siribumrungwong2
RR, EVLA vs. surgery* 1.5 0.7 3 Lognormal Siribumrungwong2
RR, RFA vs. surgery* 1.3 0.7 2.4 Lognormal Siribumrungwong2
AVVSS, pre-treatment** 14.02 9.49 19.16 Triangular Darwood3 AVVSS, 1 yr post-surgery** 3.89 0 10.29 Triangular Darwood3 AVVSS MD of EVLA or RFA vs.
surgery* -0.2 -0.93 0.62 Triangular Siribumrungwong2
%, FS maintenance† 0.6 EAG
Rate, retreat using EVLA†† 0.5 0 1 Assumption
Note:
§: treatment failure is failure to completely abolish reflux in the axial vein (refer to Table T.3 for detailed definition); *: range is based on 95% CI; **: range is based on IQR; ¶: based on expert‟s opinion; †: % of patients receiving maintenance using foam sclerotherapy; ††: % of retreatment using EVLA over RFA;
QoL: quality of life; RR: relative risk; AVVSS: Aberdeen Varicose Vein Severity Score; FS: foam sclerotherapy; IQR: Interquartile range
Costs
Health service resources included in the analysis is shown in Table E.2 and reflects 2012 Canadian dollars. Given that costs occur over 1 year period, discounting was applied with an annual rate of 5%.2 As previously stated the CEA adopted a payer perspective and considered direct medical service costs to the Alberta health system.
Cost data for conventional open surgery were obtained from two provincial administrative databases.
Physician Claims database provided data related to billing services to physicians for conducting the surgical procedure. Billing codes related to the procedure were used to estimate the average
physician cost. Note that the estimated average physician cost of surgery was also used to estimate the physician fees associated with EVLA or RFA.
The Ambulatory Care Classification System (ACCS) database provided data on outpatient hospital services for surgery. The ACCS contains patient specific cost information including drug and supply costs, and functional centre direct costs (salaries, medical, and surgical supplies) and indirect costs (e.g. facilities management, registration, patient food services, and health records). These costs were estimated by identifying surgical cases contained in the data sets using the Canadian Classification of Health Interventions (CCI) codes. Facility costs associated with EVLA or RFA were obtained from data provided by the EAG (Appendix E.2). See Appendix E.3 for CCI codes, international
classification of diseases (ICD) codes and physician claim codes used.
Table E.2: Cost inputs (2012$)
Item Mean SD Distribution Source
EVLA* $1,866.98 596.08§ Gamma EAG
RFA* $2,180.18** 596.08§ Gamma EAG
Outpatient surgery $1961.83 596.08 Gamma AH data
Doppler ultrasound $356.47 259.00 Gamma AH4
Physician† $842.97 404.02 Gamma AH data
Foam sclerotherapy $42.68 4.31 Gamma AH data
Ligation with EVLA/RFA $300.00 30.61 Gamma EAG
Follow up visit $39.94 7.96 Gamma AH data
Note:
¶: all costs are adjusted to 2012 using Alberta consumer price index (CPI).
*: Hospital costs of EVLA and RFA include procedure, overhead, administration, ultrasound and laser/radiofrequency kit. A breakdown of the cost is presented in Appendix E.2.
**: Note that costs provided by the EAG reflect the costs per leg. These were converted to a per-patient cost using information from AH data. Based on AH data, outpatient costs was $1,895.00 per patient (all leg procedures) and $1,691 for one leg procedures, indicating 1.12 times higher per-patient cost versus one leg procedures (Appendix E.2).
§: standard deviation for EVLA/RFA is assumed to be same as that of surgery
†: Surgeon cost for EVLA/RFA is assumed to be same as that of ligation with stripping
Effectiveness
Effectiveness was quantified using two measures. The first was defining effectiveness as the number of symptom free years. The second was defining effectiveness using the Aberdeen Varicose Vein Severity Score (AVVSS). The AVVSS is an instrument used to measure the health related quality of
2 If costs and/or outcomes are considered over a period of more than a year and/or the timing of costs and outcomes differ between alternatives then it is necessary to discount costs and outcomes to a common current value.
life for patients with varicose veins. Targeted domains include physical symptoms, pain, ankle oedema, ulcers, compression therapy use and the effect on daily activities. Scores on the instrument range between 0 and 100 with 0 indicating no effect with 100 indicating severe effect. Both measures of effectiveness were discounted at a rate of 5%.
Criteria for cost-effectiveness
The criteria for concluding that an alternative is cost-effective are as follows:
1. Alternatives that are both more costly and less effective compared to other alternatives are dominated and are considered NOT cost-effective. These are eliminated from further consideration.
2. Alternatives that are less costly and more effective compared to other alternatives are dominant and are considered cost-effective. These are included for further consideration.
3. Alternatives that are both more costly and more effective (or less costly and less effective) are not dominant and their cost-effectiveness is uncertain:
a. Within these alternatives there can be a situation of extended dominance. That is, among these alternatives there are some alternatives that are more cost efficient than others. Alternatives that are dominated by extension are not considered
cost-effective and are excluded from further consideration.
b. For the remaining alternatives that are not dominated by extension, cost-effectiveness is dependent on whether decision-makers deem the additional effectiveness to be worth the additional costs referred to as the cost effectiveness threshold.
Sensitivity analysis
It is important to provide information regarding the degree of variability in potential costs and effectiveness when using different values for model inputs (i.e. parameter uncertainty). Therefore, a probabilistic sensitivity analysis was conducted using 10,000 Monte Carlo simulations based on the ranges and distributions listed in Tables E.1 through E.2.
A scenario analysis was conducted to determine the impact on the cost effectiveness results by varying the proportion of EVLA versus RFA for the treatment of failures in the model.
Budget impact analysis (BIA)
The BIA was conducted to assess the cost impact of replacing eligible surgical procedures with EVLA or RFA and covering current EVLA or RFA procedures being conducted in private settings.
Data estimating the number of eligible surgical patients for EVLA or RFA (i.e. observed demand) were extracted from the ACCS for surgical procedures conducted as an outpatient procedure. Data was extracted based on the CCI code and ICD code (see Appendix E.3). Data estimating the
number of endovenous ablation procedures being conducted in private settings was provided by the EAG. See Appendix E.6 for calculations. The analysis also included the costs for retreatment associated with failures. All cost inputs applied in the BIA model were identical to those shown in Table E.3.