Nearly 700 men and women in the United States die of primary hypothermia each year. Although alcohol, drug use and older age increase the risk of hypothermia, trauma patients are far more likely to experience exposure-related complications and death.
"Hypothermic patients with multiple injuries commonly have acidosis and coagulopathy, a combination that contributes to as much as a five-fold increase in mortality," says Henry J. Schiller, M.D., a trauma and critical care surgeon at Mayo Clinic in Rochester, Minn.
"Early recognition and treatment are essential for every patient with hypothermia, but rapid intervention is especially critical for people who are injured. Because mortality and morbidity are higher, the threshold for initiating treatment is lower."
That threshold is reflected in different hypothermia classifications for injured and uninjured patients. People without injuries are considered severely hypothermic with a core temperature of 82.4 F (28 C) or lower. For injured patients, that temperature is 89.6 F (32 C) or lower. Similar differences exist for mild and moderate hypothermia.
Dr. Schiller emphasizes that early recognition of hypothermia is crucial. "Temperatures should be taken as soon as possible and treatment started immediately to restore normothermic status," he says.
Placing patients in a warm room, removing wet clothing and using forced-air heating blankets is the first step in preventing further heat loss. These measures may be enough to raise the core temperature in people with mild hypothermia, but active treatment is needed in more-serious cases.
Aggressive interventions range from warm oral liquids and heated IV solutions to gastric and peritoneal lavage. People who are profoundly hypothermic or have cardiac arrhythmias may require cardiopulmonary bypass using venovenous hemofiltration.
Dr. Schiller says that Saint Marys Hospital, one of Mayo Clinic's hospitals in Rochester and a Level I trauma center, treats about 24 hypothermic patients each year. "Some are classic hypothermia cases — people who are intoxicated or older adults who fall and are stranded outside for long periods of time."
Other cases are more unusual. "It's important to recognize that hypothermia can occur in temperatures that aren't particularly cold — 60 F (15.5 C), for example. We also know from experiences in Iraq and Afghanistan that hypothermia can occur in extreme heat due to evaporative loss. So it's not only temperature. It depends on duration of exposure, age, health status, and whether conditions are wet or dry."
He adds that all these factors must be taken into account when evaluating and treating hypothermia. "Smaller hospitals lacking resources for adequate rewarming should consider transferring trauma patients who have a registered core temperature below 96.8 F (36 C)," he says.
The same is true for hypothermic patients who are very old, very young or have multisystem disease. "In all these cases, the threshold for transfer to a higher level of care is much lower."