Working under bright lights and wearing heavy gowns can make surgery uncomfortably hot for doctors and nurses. Operating rooms, therefore, are traditionally kept quite cold. That makes the surgical patient quite cold, too--even slightly hypothermic. Body temperatures can drop by 4 degrees. Doctors used to think mild hypothermia was actually good for the patient because cold retards the growth of bacteria in the air. But according to a new study, the cold temperatures in operating rooms actually triple the risk of infection.
What causes wound infection is not really bacteria floating around in the air but the patient’s decreased resistance to bacteria on the skin or inside the body, says Daniel Sessler, an anesthesiologist at the University of California at San Francisco and the University of Vienna. To find out how operating-room temperatures affect that resistance, Sessler and his colleagues studied 200 patients undergoing colorectal surgery. In 104 patients, warmed intravenous fluid and forced-air blankets (which are like quilts with warm air blown through them) kept body temperature normal. The other 96 patients were not warmed during surgery, and their body temperature dropped to an average of 94.5 degrees.
Wound infections, Sessler found, occurred in 19 percent of the patients allowed to become hypothermic but in only 6 percent of the warmed patients. Unwarmed patients also stayed in the hospital nearly three days longer.
Hypothermia probably lowers the body’s resistance in two ways, says Sessler. First, low body temperature reduces the flow of blood--and its oxygen cargo--to the wound. Oxygen is essential to fighting infections, he says. The body’s immune system breaks down molecular oxygen into highly reactive atomic oxygen. Immune cells release this oxygen near bacteria. That is what kills them, says Sessler. Hypothermia also directly inhibits many functions of the immune system. The cells and enzymes responsible for immunity simply don’t work well when the body is cold, Sessler says.
I think warming will become the standard of care in no time, says Sessler. None of this is difficult, and none of it is expensive. Keeping people warm costs less than $30, which is nothing in the scheme of an operation. But it makes a big difference in terms of the outcome, is essentially risk free, and reduces cost. So it’s sort of a no-brainer that you should keep people warm.
