Raleigh, N.C. ? Sometime last year, elevator workers at two hospitals drained hydraulic fluid into empty soap containers and capped them without changing the labels.

Not long afterward, medical staff complained that some of their surgical tools felt slick. But it was not until January that about 3,800 patients learned that for two months their surgeons had unknowingly used instruments washed in the slippery fluid instead of soap.

Duke assured patients that the mix-up created little chance of medical problems, but a federal agency determined both hospitals – Durham Regional Hospital and Duke Health Raleigh Hospital – had endangered patients.

Since the problem became public, at least one patient has sued the elevator company complaining of severe infection, temporary loss of kidney functions and other ailments.

This week, a Raleigh lawyer began running television ads recruiting patients exposed to the fluid. About 15 or 20 former patients complaining of aching joints and infections have contacted him.

“What we really want is a response from Duke to prove their assertions that there was very little risk to the patients,” attorney Thomas Henson said. “I mean, patients are hanging out there with problems and Duke won’t give an answer to us.”

Both hospitals have created plans to prevent such problems in the future, a Duke spokeswoman said Monday. The university’s health system also includes Duke University Hospital, widely considered one of the nation’s top medical facilities.

Durham Regional Hospital in Durham, N.C., is one of two hospitals run by Duke University Health System that may have put patients in jeopardy last year by failing to detect that surgical instruments were being washed in used hydraulic fluid instead of detergent. About 3,800 patients at Duke Health Raleigh and Durham Regional hospitals were exposed to surgery with the contaminated instruments.

In January, Duke officials said the instruments had been washed in the hydraulic fluid, then run through a steam bath for sterilization. The hospital said it monitored infection rates and found no increase for the time the hydraulic fluid was used.

Other opinions on the potential harm from the fluid varied. A report by the federal Centers for Medicare and Medicaid Services said the hospitals’ errors put patients in “immediate jeopardy.”

State investigators – while citing the hospitals and the elevator company for mistakes that created the confusion, including poor communication and improper labeling of chemicals – did not consider the problem serious, said spokeswoman Heather Crews of the state Labor Department.

There is little data on how the fluids affect humans. In studies, rabbits that inhaled the fluid had trouble breathing and other animals experienced nervous system tremors and well as diarrhea and breathing problems.