How Therapeutic Hypothermia Works

Brief History of the Medical Ice Age
Many cardiac surgeons have embraced therapeutic hypothermia for decades.
Many cardiac surgeons have embraced therapeutic hypothermia for decades.
© Dr. Barry Slaven/Visuals Unlimited/Corbis

The use of therapeutic hypothermia (TH) for improving outcomes in traumatic brain injury patients dates back to 1945, roughly the same year that Captain America became trapped in icy suspended animation [source: Gibson and Andrews].


By the 1950s, open-heart surgeons were using TH as a preventative prelude to open-heart surgery. Although more recent techniques allow some cardiac surgeries to take place on a still-beating organ, historically such procedures have required stopping the heart, at least briefly. Researchers realized that hypothermia could help safeguard a patient's gray matter from the consequences of the resulting lack of blood flow (ischemia) and oxygen (anoxia) [sources: Nolan et al.; Texas Heart Institute]. Without TH, surgeons typically have less than five minutes to restore blood flow before brain damage begins to set in [source: Murphy].

Body cooling techniques are one of the two major technologies that make open heart surgeries possible. The other is the cardiopulmonary bypass machine (aka the heart-lung machine), which takes over oxygenation, carbon dioxide removal and blood pumping duties while the heart and lungs are inactive [sources: NHLBI; Texas Heart Institute].

As we'll discuss in greater detail below, TH has also seen use since the late 1950s in limiting damage to the central nervous systems of cardiac arrest patients who do not regain consciousness after the return of spontaneous circulation (ROSC) [sources: Deckard and Ebright; Gibson and Andrews]. Such benefits notwithstanding, TH's perceived ties to side effects like pneumonia, bleeding and cardiac arrhythmias left it medically sidelined until the 1990s, when experimental studies finally broke the ice by demonstrating that the technique could reduce neuronal damage and guard against cerebral ischemia [source: Gibson and Andrews].

Thereafter, research still moved at a somewhat glacial pace until the publication of two key cardiac studies in The New England Journal of Medicine in 2002. The so-called HACA (hypothermia after cardiac arrest) and Bernard studies both showed markedly improved outcomes in heart patients treated with hypothermia [sources: Deckard and Ebright; Winslow]. The studies' subjects suffered from either ventricular tachycardia, a rapid heartbeat spurred by offbeat electrical doings in the heart's lower chambers (ventricles), or ventricular fibrillation, a common heart arrhythmia in which ventricle muscles quiver haphazardly instead of performing a coordinated contraction [source: Deckard and Ebright].

In 2005, the American Heart Association (AHA) added therapeutic hypothermia to its cardiopulmonary resuscitation (CPR) guidelines [source: Deckard and Ebright; Winslow]. In 2010, they expanded these standards to include in-house cardiac arrests and patients incapable of following verbal commands after ROSC [source: Deckard and Ebright].

Uses and research continue to expand, but at its heart, TH provides a vital means of preserving the brain amid two of the harshest shocks it can suffer: the sudden loss of blood flow and its equally abrupt return.