136 Chapter 8 related differences in outcome as well as no influence due to aneurysm size or location. Patients presenting with acute SAH without presence of a ruptured aneurysm were assumed to have no other intracranial vascular pathology to be treated. Model simulation and outcome measures In our model, we evaluated the outcome of diagnostic pathways based on the input parameters in table 1. Simulation was performed for a hypothetical cohort of 1000 patients. We compared total one-year costs of diagnostic test, treatment option and health state to one year’s health benefits in terms of QALYs. Incremental cost-effectiveness ratios (ICERs) were calculated from each model, by dividing the incremental costs by the incremental QALYs. Whether a treatment is deemed cost-effective depends on how much society is willing to pay for a QALY gained. The simulation was repeated with the scenario analysis in which for all patients DSA was performed in case an aneurysm was visible but coiling was deemed not feasible. Sensitivity analysis Uncertainty regarding the model input parameters was explored with a probabilistic sensitivity analysis using Monte Carlo simulation.21,26 With Monte Carlo simulation, different samples (N=1000) are taken from parameter distributions for the hypothetical cohort to examine uncertainty in cost-effectiveness estimation.19 All assigned distributions are listed in table 1. Table 1. Model input parameters SD / Model Parameter Value range Distribution Source Discount rates cDR (Cost discount rate) 4% fixed 22 oDR (Outcome discount rate) 1.5% fixed 22 Treatment independent parameters Probabilities (p) pAneurysm in case of non traumatic SAH 0.85 beta 14 Costs (€) Diagnostics cDSA 725 € 22 cMRA 252 € 22 cCTA 197 € 22 Treatment cCoiling 28,870 € 1,833 € gamma 13 cClipping 31,739 € 2,503 € gamma 13 Health state costs number of days in nursing home per year (d) 365 costs per day in nursing home (€/d) 241 € cDisability 87,975 € 22 Event costs cDeath 2,741 € 19,24 Utilities uWell 0.78 0.019 beta 19,23 uWell after SAH 0.72 0.65-0.80 triangular 19,23
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