The buyout of Hospital Corporation of America has not stymied negotiations between workers and officials at HCA-owned West Hills Medical Center and Los Robles Medical Center in Thousand Oaks. Thea Lavin, a spokeswoman for SEUI United Healthcare Workers-West, said discussions will continue this week at the hospitals. The union is in negotiations with five HCA hospitals in California after a workers contract expired June 30. The union contends that HCA has under-staffed its facilities, which forces nurses to work overtime and put patients at risk. No strike date has been set, Lavin said. Nashville-based HCA on Monday announced that it agreed to be bought for $21.3 billion. The company is the largest hospital chain in the nation, with 276 medical centers, including nine in California. Dana Simon, administrative vice president for SEIU, said the news that HCA is up for sale “changes nothing relative to collective bargaining between HCA and our union.” HCA also owns 25 percent of Encino-Tarzana Regional Medical Center, with Tenet Healthcare Corp. owning the rest. The two groups put the facilities up for sale in 2004, although no deal has been announced.