Timing of prophylactic surgery in prevention of diverticulitis recurrence: a costeffectiveness analysis Richards R J, Hammitt J K 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 This study examined elective prophylactic resection (sigmoidectomy) for uncomplicated diverticulitis. In particular, it concentrated on the optimum timing of this intervention by considering when to conduct the elective surgery, after the first, second or third attack of diverticulitis. The use of laparoscopic techniques for this procedure was also considered. Type of intervention Secondary prevention. Economic study type Cost-utility analysis. Study population The study population comprised persons aged 60 years or older, who had recently recovered from an attack of uncomplicated diverticulitis. Setting The setting was secondary care. The economic study was conducted in the USA. Dates to which data relate The effectiveness data were obtained from articles published between 1969 and 1997. The prices used related to the 1998 fiscal year. The dates relating to resource use were not reported since the model determined this information. Source of effectiveness data The effectiveness data were derived from the medical literature and expert opinion. Modelling A Markov model with decision trees was used to calculate the costs and benefits of the various scenarios. Outcomes assessed in the review The model inputs included: the probability of a severe attack, which requires urgent surgery; the likelihood of the type of surgery performed following a severe attack; Page: 1 / 5
the surgical mortality rates, dependent on the type of procedure; the recurrence risk per cycle and post sigmoidectomy; quality of life adjustments; and the probability of death from natural causes. Study designs and other criteria for inclusion in the review The effectiveness data were obtained from observational studies. It was unclear whether the authors undertook a systematic review of the literature, with predefined inclusion and exclusion criteria, to identify relevant studies. Sources searched to identify primary studies 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 Twenty-three primary studies were included in the review. Methods of combining primary studies The results of the primary studies were not explicitly combined. Instead, clinical experts used this information as the basis for their estimates of the baseline values of the model parameters. Investigation of differences between primary studies Not investigated. Results of the review The effectiveness data were compiled in two stages. During the first stage, clinical experts read related published articles. On the basis of these findings, the clinicians then estimated baseline probabilities and identified ranges for the sensitivity analysis. On the basis of the published literature and clinical opinion, the transition probability of a severe attack was set at 0.3. Given that a severe attack had occurred, the type of surgical procedure performed depended on the Hinchey staging system. The probability of Hinchey stage I was assumed to be 0.37, stage II 0.38, and stages III or IV 0.25. Similarly, the mortality rate was dependent on the type of procedure. The mortality rate ranged from 0.005 for an elective prophylactic resection (sigmoidectomy) to 0.58 for an attempted Hartmann reversal. The recurrence risk per cycle was 0.03 (equivalent to a 5-year recurrence risk of 26%) and 0.003 following a sigmoidectomy. Adjustment factors for quality of life were applied to life expectancy. Page: 2 / 5
For the temporary states of hospitalisation and postsurgical outpatient recovery, the adjustment factors were 0.5 and 0.85 per day, respectively. The adjustment factor for colostomy was set at 0.85 per cycle. Methods used to derive estimates of effectiveness Estimates of effectiveness were obtained from a review of relevant literature and clinical opinion. Estimates of effectiveness and key assumptions The estimates of effectiveness are reported in the 'Results of the Review' section. Measure of benefits used in the economic analysis Life-years and quality-adjusted-life-years (QALYs) were used as the benefit measures in the economic analysis. The QALYs were calculated by adjusting life expectancy for quality of life in short- (hospitalisation and postsurgery outpatient recovery) and long-term (colostomy) health states. Due to the lack of published data on the quality of life in these health states, the adjustment factors were based on expert clinical opinion. Direct costs The cohort of hypothetical patients was followed from their entry into the model at the age of 60 years until their death. Consequently, the costs were discounted at a rate of 3%. The daily costs of physician involvement and hospitalisation (based on diagnostic-related groups) were reported, although the amount of these resources used was not. Cost data on both physician involvement and hospitalisation were derived on the basis of average payment and reimbursement amounts of Medicare. The quantities of resources used were determined from the model. The cost data related to the fiscal year 1998. Statistical analysis of costs The costs were treated as point estimates and, therefore, no statistical analysis was performed. Indirect Costs The indirect costs were not reported. Currency US dollars ($). Sensitivity analysis One-way sensitivity analyses were performed on all of the model parameters. The motivation for these sensitivity analyses was the uncertainty inherent in the estimation of some of the model parameters. In addition, the possibility of outpatient recurrences and performing the prophylactic resection using laparoscopic techniques were also examined. A two-way sensitivity analysis was conducted concomitantly on the severity of the attack and the 5-year recurrence risk. Estimated benefits used in the economic analysis Elective prophylactic resection following the first attack yielded 14.154 life-years and 14.143 QALYs. This was lower than that arising when the surgery was performed after the second (14.158 life-years and 14.153 QALYs) or third (14.164 life-years and 14.160 QALYs) attacks. Therefore, the incremental benefits were highest when patients received elective surgery after the third attack of uncomplicated diverticulitis. The only adverse effect of surgery that was included in the economic analysis was death. Page: 3 / 5
Cost results Elective prophylactic resection following the first attack resulted in costs of $8,183. These were higher than those incurred if surgery was conducted after the second ($3,621) or third ($2,507) attack. The costs of adverse effects were not included. Synthesis of costs and benefits Performing surgery after the third attack was found to be the least costly option and also yielded the highest health benefits. These results were generally robust to changes in the model parameters. However, when the 5-year risk of the third attack equalled 61%, performing surgery after the second attack was the optimum strategy. This resulted in an incremental cost-effectiveness ratio (ICER) of $95,000 per additional QALY saved when compared with conducting surgery after the third attack. When the model was extended to include outpatient recurrences, by setting the yearly risk of such an event at 42%, the health benefits were greater if prophylactic resection was conducted after the first attack rather than the third, although in this case, the ICER was $4,500,000. Even when the model was extended to consider performing prophylactic resection using laparoscopic techniques, the third scenario remained the dominant strategy. Authors' conclusions Performing elective prophylactic surgery after the third attack of uncomplicated diverticulitis resulted in cost-savings, and also improved health outcomes, compared with implementing such an intervention after the first or second attack. CRD COMMENTARY - Selection of comparators The comparator used was justified on the grounds that there is disagreement about the optimum timing for elective prophylactic resection following an attack of uncomplicated diverticulitis. The decision to proceed with this preventive measure essentially involves a trade-off between the increased risk of surgery and the reduced probability of recurrence. Three scenarios were compared, of which one was the current practice recommended by several organisations. Validity of estimate of measure of effectiveness The authors did not state that a systematic review of the literature had been undertaken. Effectiveness measures from published studies were used to inform the estimates derived by clinical experts. The authors did not report the precise details of the methodology used by experts to derive these estimates. The authors did not consider the impact of differences between the primary studies when estimating the effectiveness. Validity of estimate of measure of benefit The estimation of benefits was modelled. The instrument used to derive the measures of health benefit, a Markov model, was appropriate. Validity of estimate of costs The authors reported that the costs were estimated from a societal perspective, but the indirect costs were not included. In addition, some direct costs were omitted from the analysis. For example, the authors acknowledged that complications from diverticulitis (such as right-sided colon attacks of diverticulitis, bleeding, stricture formation and fistulae) and surgery, and the costs of treating these adverse events were not included. The authors concluded that the omission of these complications might have biased the results against early surgical intervention. The costs were reported separately. A sensitivity analysis of the model parameters was conducted and the ranges used appear to have been appropriate. A sensitivity analysis of the prices was not conducted. Page: 4 / 5
Powered by TCPDF (www.tcpdf.org) Other issues The authors did not make appropriate comparisons of their findings with those from other studies. The issue of generalisability to other settings was raised. The authors argued that because this analysis focused on patients aged 60 years at the commencement of the model, the results of this analysis were generalisable. The authors postulated that their results might not hold in an analysis of a younger cohort because the disease may be more serious in younger persons. The authors did not present their results selectively. The authors reported a number of further limitations to their study. First, the efficacy estimates were derived from observational studies, and the authors acknowledged that this might bias the estimates. However, the effects of these potential biases were mitigated by the sensitivity analyses performed. Second, since diverticulitis may be more serious in younger patients, early surgical intervention may be justified in these cases. By concentrating on patients aged 60 years or older, the results of this analysis are not valid for a younger cohort. Third, as already mentioned, some complications of the condition were not considered, which may have led to an overstatement of the benefits of a watchful waiting approach in favour of early surgical intervention. Finally, the authors recognised that the source of the unit costs was imperfect. Implications of the study The authors concluded that the results of their analysis supported the case for delayed surgical intervention in patients aged 60 years or older with uncomplicated diverticulitis. Source of funding Supported by the Agency for Healthcare Research and Quality, grant number R03 HS10827. Bibliographic details Richards R J, Hammitt J K. Timing of prophylactic surgery in prevention of diverticulitis recurrence: a costeffectiveness analysis. Digestive Diseases and Sciences 2002; 47(9): 1903-1908 PubMedID 12353827 Indexing Status Subject indexing assigned by NLM MeSH Cohort Studies; Cost-Benefit Analysis; Costs and Cost Analysis; Decision Trees; Diverticulitis /economics /prevention & control /surgery; Humans; Markov Chains; Medicare /economics; Middle Aged; Models, Statistical; Quality of Life; Recurrence; Sensitivity and Specificity; Time Factors AccessionNumber 22002001447 Date bibliographic record published 30/04/2004 Date abstract record published 30/04/2004 Page: 5 / 5