Conference Coverage

Simulation model favors hernia surgery over watchful waiting


Key clinical point: Surgical repair of ventral hernias at the time of diagnosis was more cost effective than watchful waiting.

Major finding: The incremental cost-effectiveness ratio for laparoscopic surgery, compared with watchful waiting, was about $14,800 per QALY.

Data source: A state-transition microsimulation model of 100,000 people.

Disclosures: This study was funded by the Resident Research Scholarship awarded by the American College of Surgeons. Dr. Wolf reported having no disclosures.



– Surgical repair of ventral hernias at time of diagnosis is a more cost-effective approach than watchful waiting, according to the results of a state-transition microsimulation model presented by Lindsey Wolf, MD, at the annual clinical congress of the American College of Surgeons.

The benefit of surgical intervention, compared with observation or watchful waiting for reducible ventral hernias is not well described, reported Dr. Wolf, a general surgery resident at Brigham and Women’s Hospital, Boston.

Dr. Lindsey Wolf

Decision analysis comparing lifetime outcomes after surgical repair of hernias or watchful waiting are scarce. Dr. Wolf and her associates attempted to fill this gap by creating a Markov model that estimated outcomes and cost effectiveness for 100,000 simulated patients with any type of reducible ventral hernia who underwent either watchful waiting, open repair at diagnosis, or laparoscopic repair at diagnosis.

In the model, cost was represented in U.S. dollars and benefit was indicated by quality-adjusted life years (QALY). Both measures accumulated for individual patients over time and then were averaged and reported for an entire cohort of simulated patients, Dr. Wolf explained. Incremental cost effectiveness, a measure represented as a ratio of cost per QALY gained for each strategy, “provides context by allowing us to compare each strategy to the next best strategy,” explained Dr. Wolf.

Willingness to pay, a threshold set by the government that represents the maximum amount a payer is willing to spend for additional quality, was set at a threshold of $50,000 dollars per QALY, which is a “commonly accepted willingness-to pay-threshold,” she said.

The model’s primary outcomes were lifetime costs, QALYs from time of diagnosis, and incremental cost-effectiveness ratios.

“We built a state-transition microsimulation model which represents the different health states a patient can occupy at any point in time,” Dr. Wolf reported. “Using a yearly cycle, a cohort of patients were simulated through the model one at a time.”

All patients entered the model in an asymptomatic state. For each year there was a probability for a patient to transition from the current state to another state in the model.

Patients who underwent surgical repair at diagnosis were transitioned to the no-hernia state in the first year after undergoing surgery. Those in the watchful-waiting group stayed in the asymptotic state and each year there was a probability of becoming symptomatic. Of those who became symptomatic, there was a small probability that they would present with an incarcerated hernia and would require emergent surgery rather than elective surgery. Patients were subjected to perioperative mortality rates, as well as background yearly risk of death.

Cohort characteristics, hospital and other costs, perioperative mortality, and quality of life were derived from best available published studies and the Nationwide Inpatient Sample, the largest all-payer inpatient care database in the United States.

Overall, laparoscopic surgery at diagnosis was the optimal hernia repair strategy, reported Dr. Wolf.

Although laparoscopic surgery was the most expensive, it was also the most effective and, compared with watchful waiting – the least expensive and least effective strategy – the incremental cost-effectiveness ratio was about $14,800 per QALY.

Open repair at diagnosis fell between the watchful-waiting and laparoscopic-repair strategies in terms of cost and effectiveness.

To understand the conditions in which the optimal strategy changed, the researchers performed sensitivity analysis using the net monetary benefit metric, which represented both costs and benefits in a single unit at a given willingness to pay threshold.

“For a cohort of high-risk patients, once the perioperative risk of death exceeds 3.4%, watchful waiting becomes the preferred strategy,” Dr. Wolf said. Watchful waiting also was the preferred strategy when the yearly risk of recurrence exceeded 24%.

A sensitivity analysis comparing quality of life for elective open and laparoscopic repair revealed that, when quality-of-life measures were similar between the two surgical repair groups, the open repair became the preferred strategy.

Finally, researchers performed probabilistic sensitivity analysis by simulating the cohort of 100,000 patients 100 times and each time deriving results that were similar – an indication of robust results.

“In conclusion, we found that, for a typical cohort of patients with ventral hernia, laparoscopic repair at diagnosis is very cost effective. As long-term outcomes for open and laparoscopic repair were very similar in the model, the decision between laparoscopic and open surgery depends on surgeon experience and preference for one method over another,” said Dr. Wolf.

This study was funded by the Resident Research Scholarship awarded by the American College of Surgeons. Dr. Wolf reported having no disclosures.

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