As mountain rescue teams, we are all familiar with the management of accidental hypothermia. It involves a well-established series of activities, including rewarming the subject, providing calories and hydration, and removing the subject from the field. Rescuers typically provide whatever calories they have on hand, with a classic choice being hot cocoa and some sort of high calorie, carbohydrate-rich snack.
The concept of offering calorie-dense food and beverages to the hypothermic patient is not new; it is mentioned in the Wilderness Medicine Society’s (WMS) Clinical Practice Guidelines for hypothermia management and in 2022 Dr. Aaron Billin authored an excellent article for the WMS magazine exploring the thermodynamics of oral resuscitation in hypothermic patients. While the current approach to management isn’t wrong, several physicians (myself included) and dieticians recently revisited the topic to see whether it might be possible to better define a hypothermic subjects’ carbohydrate needs and provide guidance as to the type and amount of carbohydrates being provided in the field, as well as the timing.
Specific guidance doesn’t currently exist, and data is hard to come by. However, we believe this is a topic worth considering, given the known complications of hypoglycemia in the setting of hypothermia and rewarming. Our goal was to see if rescuers could be doing more to ensure optimal patient outcomes.
The metabolic effects of hypothermia and rewarming
When a person’s body detects “cold,” the brain initiates measures intended to regulate temperature and energy balance. This begins with activation of brown adipose tissue, followed by shivering. The shivering response raises an individual’s metabolic rate to two to five times their baseline and is typically sustainable for a matter of hours, after which time glycogen stores become depleted.
At this point, the body shifts to a state of insulin resistance in order to protect critical organ functions, particularly that of the brain, which primarily uses glucose for fuel. As hypothermia progresses, the metabolic rate slows by 5-7% per degree Celsius decrease of core body temperature. Cognition, judgment, focus, and coordination begin to deteriorate. A patient may paradoxically lose their drive to eat and drink, worsening their overall metabolic picture. It can be challenging to separate which of the patient’s signs and symptoms are related to hypothermia versus hypoglycemia, as significant overlap exists.
As rewarming begins, the body rapidly shifts out of its protective insulin resistant state, leading to a potentially abrupt drop in blood sugar as well as critical electrolyte abnormalities. It is hard to predict exactly how much a patient’s blood sugar may drop with rewarming. It appears to be influenced by a number of factors, including age, underlying medical conditions (e.g. diabetes), caloric balance leading up to and during development of hypothermia, and rate of rewarming. Greater fluctuation is expected in diabetics, as well as those who are rewarmed at a rapid rate.
Data is scarce when it comes to blood glucose measurements in hypothermic patients, particularly in the out-of-hospital setting. Most of the existing data comes from an intensive care unit (ICU) or operative environment, in the context of intentional (“therapeutic”) cooling for post-cardiac arrest patients and those undergoing cardiothoracic procedures.
One study conducted in an ICU setting suggested blood glucose decreases of up to 100 mg/dL may not be unheard of during early rewarming, if not corrected. There is also a case report in the emergency medicine literature describing similar rewarming-related hypoglycemia following an avalanche burial, with a decrease in blood sugar reaching the triple digits.
Potential risks of low blood sugar in hypothermic patients
The immediate risks of low blood sugar far outweigh the risks of high. Hypoglycemia stalls thermogenesis, which can worsen the overall cold state. As previously mentioned, the brain relies on glucose as its primary source of fuel. Low blood sugar leads to impaired functioning – which can complicate subject evacuation – and may cause seizures.
Discussed less often are the cardiac implications of sudden shifts in blood glucose and electrolytes. We know that hypothermia predisposes subjects to arrhythmias, and as rescuers we are trained to handle hypothermic patients with care. However, an abrupt decrease in blood sugar – such as that which can occur with rewarming – leads to brisk activation of the sympathetic nervous system (our “fight or flight mechanism”), followed by concurrent activation of the parasympathetic nervous system in cases of extreme hypoglycemia. This can strain an already delicate heart and further predispose subjects to arrhythmias and ischemic events. In cases of accidental hypothermia, avoidance of hypoglycemia is one of the more manageable ways to prevent cardiac, metabolic and neurologic complications.
Guidance for managing blood glucose management in hypothermic subjects
In our effort to develop guidance for blood glucose management in hypothermic subjects, we took into consideration a number of factors, including the recommended dosing of, and indications for, products such as glucose gels and tabs; estimation of adult carbohydrate requirements in the setting of hypothermia and rewarming; and range of blood glucose fluctuations in available studies and case reports. Our suggestions are intended for a non-diabetic adult population, able to tolerate oral intake and not at risk of refeeding syndrome.
Initial management considerations
Avoid overly rapid rewarming, which appears to increase the risk of hypoglycemia.
Glucometers and continuous glucose monitors (CGMs) may deliver inaccurate readings in the cold. Improvement in symptoms should ultimately guide management, with or without glucometer data.
If the patient’s symptoms are not improving with seemingly reasonable interventions, always consider alternative explanations (e.g. unrecognized head injury, intoxication).
Hydration is important. Women need approximately 2.7 L/day of fluid at baseline, and men require approximately 3.7 L; these requirements increase in the setting of environmental losses.
Carbohydrate administration
Overall approach: start by giving rapid-acting (“simple”) carbohydrates to help raise blood glucose and prevent hypoglycemia during the early stages of rewarming. From there, shift toward a mixture of rapid-acting and longer-acting (“complex”) carbohydrates along with protein and fat. The latter is intended to help stabilize blood glucose during the remainder of the rewarming phase and evacuation from the field.
Begin with an initial “load” of 20-30 grams of simple carbohydrates. Examples: two tubes of glucose gel, one packet of electrolyte gel or one serving of gel blocks, 5-6 Lifesavers, or 16 oz of Gatorade. Avoid foods high in fiber (e.g. dried fruit) and fat (e.g. chocolate), which can blunt carbohydrate absorption. Avoid or limit caffeinated products as they can worsen peripheral vasoconstriction and lead to increased cold diuresis.
Wait 15 minutes to ensure oral intake is tolerated, then give another 20-30 grams of simple carbohydrates. This is based on the well-known “15/15” rule for hypoglycemia management, with slightly higher carbohydrate dosing to account for environmental stressors.
Following the second dose, wait 15 more minutes and reassess the patient. If they are improving, transition to a mixture of simple and complex carbohydrates, adding in small amounts of fat and protein. Examples: nut butter (including Nutella) with crackers, or a peanut butter and jelly sandwich; a granola bar; a prepackaged protein drink. There are also newer long-acting energy gels and drink powders on the market, containing a unique cornstarch-like ingredient that provides a steady supply of easily digestible carbohydrates.
Once a subject appears stable, it is reasonable to allow them to eat and drink at their own discretion, albeit in moderation. We suggest continued avoidance of foods that are very high in protein or hard to digest, such as beef jerky.
Keely Coxon, M.D. is an internal medicine physician and member of Everett Mountain Rescue (Wash.)
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