Eighteen patients who had operations at Duke hospitals in 2004 have sued North Carolina-based Duke University Health System. The patients charge that Duke committed fraud and negligence in connection with the patients' exposure to surgical instruments mistakenly washed in elevator hydraulic fluid. The suit asks that Duke and other defendants pay an undisclosed amount in compensatory and punitive damages. The plaintiffs are among more than 3,600 patients of Durham Regional or Duke Raleigh hospitals who were operated on with the tainted surgical tools.