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 nearly 4,000 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.
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.
At least one medical expert questioned how the error could happen and how it was allowed to persist through 3,800 operations performed in November and December.
"It should be pretty easy to see when you start to wash something that detergent is different from hydraulic fluid," said Dr. Michael Grodin, director of medical ethics at the Boston University School of Medicine. He said the two fluids normally have different colors and textures.
"The more interesting question was what was going on and why did it take so long to figure it out," Grodin said. "What was in place that people did not follow and what is being done to make sure it never happens again?"
Some hydraulic fluids have an oily smell while others have no smell, according to the federal Agency for Toxic Substances and Disease Registry. They can also be flammable.
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.
"It's pretty toxic stuff," Grodin said.
Duke has struggled with patient safety issues since February 2003, when a surgeon accidentally transplanted a heart and lungs of the wrong blood type into 17-year-old Jessica Santillan. She later received a second transplant but soon died.
A federal inspection prompted by Santillan's death found toxic chemicals stored next to food and other problems. Later that year, two infants were burned in separate incidents in the hospital's neonatal intensive care unit.
After the problems were revealed, Duke officials pledged major changes to the hospital's patient safety programs to avoid a potential loss of more than $300 million in Medicare and Medicaid reimbursements.
Associated Press Writer Valerie Bauman in Raleigh, N.C., contributed to this story.