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Cost-effectiveness of continuous positive airway pressure therapy for moderate to severe obstructive sleep apnea/hypopnea |
Ayas N T, FitzGerald J M, Fleetham J A, White D P, Schulzer M, Ryan C F, Ghaeli R, Mercer W, Cooper P, Tan M C, Marra C A |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The study examined continuous positive airway pressure (CPAP) for the treatment of patients with obstructive sleep apnea/hypopnea (OSAH). CPAP was delivered via a device that consisted of a mask, or mask alternative, worn on the face and connected to a flow generator with plastic tubing.
Study population The study population comprised drivers (aged 25 to 55 years) with newly diagnosed moderate-to-severe OSAH.
Setting The setting was primary and secondary care. The economic study was carried out in the USA.
Dates to which data relate The effectiveness data were derived from studies published between 1992 and 2005. No dates for the resource use data were reported. The price year was 2003.
Source of effectiveness data The effectiveness evidence was derived from a synthesis of published studies.
Modelling A state-transition Markov model was used to compare the costs and outcomes of OSAH treated with CPAP with no therapy in a hypothetical cohort of drivers. The time horizon of the model was 5 years and each Markov cycle lasted one year. Each year, a patient could have an MVC resulting in property damage, injury, or death, or they could die of natural causes, or could survive incident-free. Injuries were sub-classified into severity categories according to the Maximum Abbreviated Injury Scale (MAIS), with scores ranging from 1 (minimal injury) to 5 (most severely injured). The MVC survivors with the most severe injuries were unable to drive afterwards and were at no risk of a subsequent MVC. All other survivors were at risk of a subsequent MVC. A schematic of the model was presented in the paper.
Outcomes assessed in the review The outcomes estimated from the literature were:
the age distribution of male and female drivers eligible for treatment;
the rates of MVCs;
the severity of MVC injury;
the impact of CPAP on MVC rates;
the compliance rate;
the mortality rates; and
the utility values.
Study designs and other criteria for inclusion in the review A review of the literature was undertaken to identify primary studies on the effectiveness of CPAP on MVCs. Other data were derived from selectively identified studies, including a primary referral centre for OSAH in Vancouver, British Columbia (a sample of 99 patients admitted from 2003 to 2004), and the National Highway Traffic Safety Administration. Life expectancy was obtained from US life tables. Utility weights in the base-case were estimated from a study that used the standard gamble approach. Effectiveness studies were included if they compared rates of MVC (by self-report or by more objective measures such as insurance databases) in patients with OSAH before and after the initiation of CPAP therapy. Review articles and studies that reported changes in driving performance by simulator rather than actual MVC rates were excluded. Details on the number of patients and the mean age of the sample of each study included in the review were reported (total number of patients 1,227).
Sources searched to identify primary studies MEDLINE was searched from 1966 to March 2005 using the terms "sleep apnea syndromes" AND "positive pressure respiration" OR "continuous positive airway pressure" AND "automobile driving" OR "accident".
Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included Overall, 16 primary studies provided the clinical data. Eight of these were identified from the review on the effectiveness of CPAP.
Methods of combining primary studies A random-effects meta-analysis was used to pool primary estimates of effectiveness.
Investigation of differences between primary studies A test of homogeneity was performed on the 8 studies included in the meta-analysis. No significant heterogeneity was found.
Results of the review The proportion of male patients was 14% for the age class 25 - 34 years, 5% for 35 - 44 years, and 34% for 45 - 54 years.
The proportion of female patients was 5% for the age class 25 - 34 years, 34% for 35 - 44 years, and 8% for 45 - 54 years.
The severity of MVC injury was distribution as follows: 85.6% for MAIS 1, 10.5% for MAIS 2, 3.3% for MAIS 3, 0.4% for MAIS 4, and 0.2% for MAIS 5.
The utility value with no CPAP was 0.32 and the incremental gain from CPAP was 0.23.
The utilities associated with specific values of MAIS were 0.93 for MAIS 1, 0.89 for MAIS 2, 0.84 for MAIS 3, 0.93 for MAIS 4, and 0.19 for MAIS 5.
The compliance rate was 70% CPAP therapy reduced MVCs by a factor of approximately 7 (odds ratio 0.15, 95% confidence interval, CI: 0.10 to 0.22).
The MVC rate in patients with OSAH receiving CPAP treatment equalled that in the general population.
Measure of benefits used in the economic analysis The summary benefit measure used was the expected number of quality-adjusted life-years (QALYs). These were estimated by adjusting survival data by utility weights. A discount rate of 3% was applied.
Direct costs The analysis of the direct costs was considered from the perspective of the third-party payer. It included the costs associated with CPAP (e.g. CPAP device, mask, tubing, headgear and heated humidifier), specialist consultations, general practitioner (GP) visits and costs associated with MVCs. The latter covered medical and emergency services (not broken down), as well as legal costs and insurance administration costs. Lifetime medical costs depended on the MAIS level. The unit costs and the quantities of resources used were presented separately only for some items. The authors made some assumptions about the life of a standard CPAP machine (5 years). The sources of other resources were not reported. CPAP costs were derived from Medicare fee schedules. The costs of MVCs were obtained from a technical report from the National Highway Traffic Safety Administration. The authors stated that other costs were valued at market prices. Discounting was relevant, as long-term costs were considered, and an annual rate of 3% was applied. All costs were adjusted to 2003 values using the medical care component of the Consumer Price Index.
Statistical analysis of costs The costs were treated deterministically.
Indirect Costs The indirect costs were included in the analysis as a societal perspective was adopted. The indirect costs of MVCs were obtained from a technical report from the National Highway Traffic Safety Administration. Market productivity was valued in terms of lost wages and benefits. Lost household activity was valued at the market price for hiring a person to accomplish the same tasks. As in the analysis of the direct costs, the price year was 2003 and an annual discount rate of 3% was applied.
Sensitivity analysis A univariate sensitivity analysis was performed to assess the robustness of cost-utility ratios to variations in some model inputs. The model inputs investigated included probability of compliance with CPAP, utility values, the discount rate for costs and QALYs, the cost-scaling factor for adjusting lifetime costs to the 5-year time horizon, and the reduction in the rates of MVC. Alternative values were either fixed by the authors or derived from secondary sources. Alternative utility values were based on the EuroQol EQ-5D. The issue of uncertainty was dealt with by carrying out a probabilistic sensitivity analysis, in which probabilistic distributions were assigned to all model inputs in order to generate 1,000 incremental cost and effectiveness pairs. Distributions were appropriately reported for all parameters.
Estimated benefits used in the economic analysis The expected QALYs were 2.22 (95% CI: 0.86 to 3.9) with CPAP and 1.47 (95% CI: 0.28 to 3.08) with no intervention (difference 0.75).
Cost results From the perspective of the third-party payer, the expected costs were $4,177 (95% CI: 2,804 to 6,957) with CPAP and $1,659 (95% CI: 283 to 3,936) with no intervention (difference 2,519).
From the perspective of society, the expected costs were $7,123 (95% CI: 4,324 to 11,906) with CPAP and $6,887 (95% CI: 3,113 to 14,843) with no intervention.
Synthesis of costs and benefits An incremental cost-utility ratio was calculated to combine the costs and QALYs of the alternative strategies.
The incremental cost per QALY gained with CPAP in comparison with no treatment was $3,354 (95% CI: 1,062 to 9,715) from the perspective of the third-party payer and $314 (95% CI: from cost-saving to 6,114) from the perspective of society.
The results of the probabilistic sensitivity analysis favoured the CPAP strategy in all simulations and at a willingness-to-pay of $50,000 per QALY (using both perspectives). In 42% of the simulations, the CPAP strategy was dominant (both more effective and less expensive) from the perspective of society.
The deterministic sensitivity analysis suggested that the base-case results were robust to variations in most model inputs. The choice of the perspective was as critical as the selection of the utility values. When EQ-5D utilities were used instead of standard gamble utilities, the cost-utility ratios increased more than 5 times.
Authors' conclusions Continuous positive airways pressure (CPAP) was a cost-effective treatment for patients with obstructive sleep apnea/hypopnea (OSAH) in the USA. The estimated cost-utility ratio compared favourably with that of other publicly funded therapies. The authors stated that the current findings were conservative as the analysis might have underestimated other benefits of CPAP (e.g. improvements in work productivity, reduction in occupational injuries, reduced use of antihypertensive medication).
CRD COMMENTARY - Selection of comparators The choice of the comparator (no treatment) was appropriate for assessing the impact of the intervention examined in the study. Moreover, the authors stated that CPAP was the primary therapy for OSAH. You should decide whether they are valid comparators in your own setting.
Validity of estimate of measure of effectiveness The clinical data used to populate the decision model were obtained from published studies. Data on the effectiveness of treatment were derived from a meta-analysis of published studies, and details of the study population were given. The authors reported the methods and conduct of the review of the literature and the inclusion criteria adopted. They noted that most studies relied on a before-and-after design, which represents a weak source of data. A test of heterogeneity showed that the primary studies were comparable. The issue of the variability of clinical inputs was addressed in the sensitivity analysis. In general, the review of the effectiveness evidence was conducted satisfactorily and was very well reported.
Validity of estimate of measure of benefit QALYs were an appropriate benefit measure because they capture the impact of the interventions on both quality of life and survival. In addition, they can be compared with the benefits of other health care interventions. The instrument used to derive utility was reported, as was extensive information on the source of the utility weights. An alternative approach to the calculation of QALYs was used in the sensitivity analysis. Discounting was applied in accordance with economic evaluation guidelines recommended in the USA.
Validity of estimate of costs The primary analysis of the costs was carried out from the perspective of the third-party payer, but a societal perspective was also adopted in a secondary analysis. The choice of the two perspectives was therefore appropriate, and the costs included were consistent with the two analyses. Resource use was reported separately from the unit costs for some items, but most costs were presented as macro-categories. The source of the costs was given, whereas the source of data on resource consumption was less clear. Some assumptions were also made. Probabilistic distributions were assigned to costs in the stochastic sensitivity analysis, and the impact of varying specific cost estimates was investigated in the deterministic sensitivity analysis. The price year was reported, which will facilitate reflation exercises in other time periods.
Other issues The authors stated that their findings confirmed those from previous studies, which had demonstrated the cost-effectiveness of CPAP. The issue of the generalisability of the study results to other settings was not explicitly addressed, although the extensive use of sensitivity analysis enhanced the external validity of the study. The authors noted some limitations of the analysis, such as the potential for confounding in some sources of clinical data and the fact that most patients included in the primary studies had severe OSAH. Therefore, caution should be exercised if extrapolating the results of the study to the general population of patients with OSAH.
Implications of the study The study results support the use of CPAP for the treatment of patients with OSAH.
Source of funding Supported by the Michael Smith Foundation for Health Research, the Canadian Institutes of Health Research and the British Columbia Lung Association.
Bibliographic details Ayas N T, FitzGerald J M, Fleetham J A, White D P, Schulzer M, Ryan C F, Ghaeli R, Mercer W, Cooper P, Tan M C, Marra C A. Cost-effectiveness of continuous positive airway pressure therapy for moderate to severe obstructive sleep apnea/hypopnea. Archives of Internal Medicine 2006; 166: 977-984 Other publications of related interest Mar J, Rueda JR, Duran-Cantolla J, et al. The cost-effectiveness of nCPAP treatment in patients with moderate-to-severe obstructive sleep apnoea. Eur Respir J 2003;21:515-22.
Sassani A, Findley LJ, Kryger M, et al. Reducing motor-vehicle collisions, costs, and fatalities by treating obstructive sleep apnea syndrome. Sleep 2004;27:453-8.
Tousignant P, Cosio MG, Levy RD, Groome PA. Quality adjusted life years added by treatment of obstructive sleep apnea. Sleep 1994;17:52-60.
Indexing Status Subject indexing assigned by NLM MeSH Adult; Canada; Continuous Positive Airway Pressure /economics; Cost-Benefit Analysis; Female; Humans; Male; Markov Chains; Middle Aged; Quality of Life; Quality-Adjusted Life Years; Severity of Illness Index; Sleep Apnea, Obstructive /diagnosis /economics /therapy AccessionNumber 22006008205 Date bibliographic record published 31/12/2006 Date abstract record published 31/12/2006 |
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