Therapeutic hypothermia requires balancing a ticking clock against the limits of how fast a body can be safely cooled or warmed. During the procedure, a patient is brought to target temperature quickly, kept in the desired range without fluctuations, and rewarmed slowly and steadily. These three steps define the three phases of therapeutic hypothermia: induction, maintenance and rewarming. Although the ideal duration of hypothermia remains unknown, the standard procedure lasts no more than 24 hours [sources: Adler at al.; Deckard and Ebright].
To prepare the patient for cooling, doctors increase sedation and watch for shivering. Shivering, the body's attempt to maintain its proper temperature, bumps up metabolic activity, increases oxygen consumption and raises body heat, so doctors block it with a paralytic [source: Deckard and Ebright].
Throughout the process, doctors may use one of several cooling technologies. During the cooling phase, ice packs placed around the armpits, chest, groin and sides of neck offer an inexpensive solution, but can cause undesirable high and low temperatures and require a lot of attention [sources: Adler at al.; Deckard and Ebright; Gibson and Andrews]. More invasive options, such as rapid intravenous infusions of chilled saline solution or cooling catheters, offer better temperature control but bring risks of their own[sources: Deckard and Ebright; Gibson and Andrews].
If the induction stage is not properly handled, patients can develop arrhythmias, including bradycardia (very slow heart rate), atrioventricular blocks (lags in the electrical signal between the atria and ventricles), and atrial and ventricular fibrillation [source: Deckard and Ebright].
During the maintenance phase, cooling might be handled noninvasively, by sandwiching the patient between special cold-water or cold-forced-air blankets, or wrapping their trunk, back and thighs in hydrogel-coated pads that circulate temperature-controlled water. Doctors might also continue core cooling using a catheter [source: Adler at al.; Deckard and Ebright; Gibson and Andrews; Resuscitation Central].
This phase, too, runs the risk of arrhythmias if not properly handled. The problem involves electrolytes (potassium, magnesium, calcium and phosphate), which move into and out of cells during temperature shifts and create harmful imbalances. Doctors handle this problem through electrolyte replacement and careful monitoring during the maintenance phase [sources: Deckard and Ebright; Delfin; Kupchik].
During rewarming, the patient's temperature is raised at a crawl -- around 0.27 to 0.90 F (0.15 to 0.50 C) per hour [sources: Adler at al.; Deckard and Ebright]. If employing cooling pads, doctors can gradually bump up the water temperature within until body temperature hovers at low normothermia for one hour. During or shortly after this period, depending on methods used, doctors will discontinue the paralytic and sedative drugs [source: Adler at al.]
In all phases, staff carefully monitors core body temperature, fluid levels and other key indicators. Afterward, recovery requires extensive nursing and management care in an intensive care unit (ICU). Just how long varies, but expect a stay of around four days to a week [source: Delfin].