(CBS) — The 45-year-old Amtrak conductor who was critically wounded May 16 while working on the eastbound Southwest Chief, at the Naperville station, is undergoing a second round of major surgery overnight.

Edward Hospital Medical Director Dr. David Piazza describes the operation taking place on conductor Michael Case, of Homewood, as “car wash surgery.”

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He says the goal is to clean out anything that could cause infection, such as fluids that spilled from one organ to the next at the time he was wounded.

Piazza said the surgery could take anywhere up to six hours to complete.

The first round of surgery, the night of the shooting, took six hours and required six units of blood.

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Piazza said doctors expect this round of surgery to go smoothly, but said it will not be the last.

He said that over the next two months, Case can be expected to undergo two more operations. When he is released, he will be transported to a rehabilitation center that will have to teach him again to walk and other basic daily functions.

He said most people who sustain wounds to the abdomen of the type Case endured die before doctors can treat them. Piazza said the bullet that struck Case missed two major veins by “millimeters.”

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The reputed gunman, 79-year-old Edward Klein, of West Allis, Wis., a retired federal protective services officer who was ticketed through to Milwaukee but attempted to leave the train at Naperville, remains jailed in lieu of $1.5 million bond.