Mom was wrong – you won’t catch your death of cold
Therapeutic hypothermia is a hot topic at this year’s ILCOR conference in Dallas. The new treatment has garnered increased attention following two papers published in the New England Journal of Medicine in 2002 (Bernard et al, 2002; the HACA group, 2002). It was also depicted in the 5th season finale of House when Wilson suggests it during an ambulance transfer of comatose Amber.
Therapeutic hypothermia is an intervention for Px who have suffered from cardiac arrest and have been successfully revived as defined by spontaneous return of circulation (SROC). It is not used to treat the arrest itself but rather to reduce the secondary injuries that ensue after the Px is brought back from the clinically dead. Basically if someone has a heart attack and is then brought back to life their body is cooled down to hypothermic levels for a day to prevent their body from hurting itself.
Cardiac arrest in general is not something many people survive. An even smaller percentage, approximately 0.9-12%, are able to walk out of the hospital with neurological function intact (ref: Arrich et al, 2009). As our brains and bodies are deprived of oxygen, even as short a timeframe as three minutes, many bad things begin to happen. Our body’s inflammatory response can cause raised intracranial pressure as well as cerebral oedema; Cells known as free radicals are created that can destroy neurological tissue; And the membranes of normal cells can wither and die (ref: Baubin et al, 2009). By cooling the Px body therapeutic hypothermia prevents some of these secondary insults.
The process of therapeutic hypothermia involves intentionally reducing the body’s core temperature from 37℃ to 33-34℃ for 12-24 hours after ROSC. At this temp there is an 18-21% reduction in the brain’s metabolic demand. This can help limit anoxic damage to a lesser extent and to fewer cells. Chilled cells also act like last week’s meatloaf in the fridge. Their cell membranes remain intact meaning less irreversible cell death (ref: Jones, 2009).
Yes but surely this must involve some complicated process with thousands of dollars of machinery? As with many new interventions a few companies have begun marketing expensive cooling machines (i.e. Arctic Sun). Although devices such as these, or intravenous catheter systems, are necessary in the ICU to maintain the Px temp at a constant level the beginning of treatment in a pre-hospital setting is much simpler. The existing studies have suggested paramedics administer chilled IV fluids (normal saline or ringer’s lactate), possibly remove the Px clothing and apply ice packs to the neck, armpits and groin. Once at the hospital the Px is also sedated and chemically paralyzed to inhibit the body’s attempt, through shivering, to rewarm (ref: Jones, 2009).
The success rate of therapeutic hypothermia is surprising. One in seven Px who are chilled will survive with, what Kevin Jones, MD terms, a positive Samsonite sign. This means instead of “surviving” a cardiac arrest, only to end up a vegetable, they are able to pull their own luggage as they walk out of the hospital. Unfortunately both the medical and the pre-hospital communities have been slow to adopt the treatment. The evidence suggests ILCOR will introduce therapeutic hypothermia as an official ALS intervention at this year’s conference. Ambulances may need to be retrofitted with small RV style fridges (also great for housing snacks) to keep a few bags of IV fluid cool. And as John Burton, MD suggests it may even change our basic ABC treatment algorithms for cardiac arrest (ref: Burton, 2009)