All horses trained by Mike Mitchell will undergo 24 hour surveillance before racing after one of his horses tested positive for an excessive amount of TC02, which is the total carbon dioxide in plasma from a blood sample obtained pre-race.The process of raising carbon dioxide levels to reduce fatigue is commonly called milkshaking.Tricky Day, a horse trained by Mitchell, exceeded the permitted TC02 level July 4 at Hollywood Park, according to a statement issued by Del Mar racetrack. The 4-year-old Phone Trick gelding won the allowance race in wire-to-wire fashion by a nose and paid $12.After the testing review committee completed its meetings with Mitchell, it was determined that all horses entered to race by him will be under 24 -hour surveillance by Del Mar security personnel beginning the day before any horse is to race. This surveillance will continue for period of 30 days beginning with horses entered for Aug. 3 and extending to Sept. 1. This will be followed by an additional 15 days of special surveillance.According to the release, this is the first TCO2 test exceeding the permitted level in Southern California in nearly five months and more than 5,000 starts.The samples are analyzed post-race at the Maddy Laboratory at the University of California at Davis. A TCO2 level of 37mml/l or higher exceeds the permitted level of TC02 by contractual agreement between Hollywood Park, Thoroughbred Owners of California, and CTT. The contract requires that any decisions by the TC02 testing review committee be implemented by subsequent race meets in the event necessary.The TCO2 Testing Review Committee includes Dr. Rich Arthur, (chair, Oak Tree), Ron Charles (MEC), George Haines (MEC), Craig Fravel (DMTC), Eual Wyatt (Hollywood Park), Drew Couto (TOC) and Ed Halpern (CTT).