Essence and goals of medical hibernation
Controlled hypothermia represents artificial, strictly regulated cooling of the body. It can be either general or local.
Key goals of this intervention:
- Significant reduction in metabolic intensity.
- Suppression of the functional activity of tissues, organs, and physiological systems.
- Multiple increase in the resistance of cellular structures to hypoxia (oxygen deprivation).
Application in surgical practice
General controlled hypothermia is vital during surgical interventions that require temporary cessation or severe reduction of blood circulation. These are so-called surgeries on "dry" organs (for example, on the heart or brain).
The pathophysiological meaning is that under cold conditions, tissue resistance increases to such an extent that an organ can be completely disconnected from blood supply for several minutes. After the manipulations are completed, its viability and adequate functioning are fully restored.
Two levels of cooling are distinguished:
- Standard level: the patient's rectal temperature is lowered to 30–28 °C.
- Deep hypothermia: used for prolonged surgical manipulations. Requires connection to a cardiopulmonary bypass machine (CPB), the use of muscle relaxants, and specific metabolic inhibitors.
Treatment of accidental hypothermia: etiotropic approach
If hypothermia occurred not for medical purposes, rescue tactics depend on the stage of the process. At the compensation stage, it is sufficient to stop the exposure to cold and warm the person (warm bath, dry warm clothing, heating pads, hot drinks). At the decompensation stage, intensive therapy based on etiotropic, pathogenetic, and symptomatic principles is required.
Etiotropic treatment is aimed at eliminating the cooling factor. The victim is immediately moved to a warm room, changed into dry clothes, and active warming is initiated.
Warming methods:
- External.
- Internal (via the stomach, rectum, lungs).
- Combined (combining external and internal methods yields the greatest effect).
Important rule: active warming must be stopped as soon as the rectal temperature reaches 33–34 °C. If the procedure is continued, there is a high risk of developing hyperthermia, since the thermoregulatory system cannot immediately restore its normal function.
Pathogenetic therapy of hypothermia
This stage is aimed at blocking the mechanisms of development of the pathological process. It includes three main areas:
- Restoration of effective circulation and respiration. Patency of the airways is ensured (removal of mucus, elimination of a fallen-back tongue), assisted or artificial pulmonary ventilation (APV) with air or oxygen-enriched mixtures is performed. In case of cardiac arrest, closed-chest cardiac massage and defibrillation are indicated. In case of concomitant blood loss, the circulating blood volume is replenished (transfusion of blood, plasma, plasma substitutes).
- Correction of acid-base balance (ABB) and fluid balance. Balanced salt and buffer solutions (e.g., sodium bicarbonate) are administered, as well as solutions of dextran of various molecular weights (Polyglucukin, Rheopolyglucukin).
- Elimination of glucose deficiency. The patient is administered glucose solutions of various concentrations in strict combination with insulin and vitamins.
Symptomatic treatment and prevention
Symptomatic therapy combats changes that worsen the victim's condition. Doctors relieve severe headaches, normalize diuresis, prevent edema of internal organs and tissues, and treat concomitant diseases and frostbite.
For the prevention of hypothermia (including in a hospital setting), it is necessary to maintain thermal balance:
- Control optimal temperature and humidity in the room.
- Use dry and warm bedding.
- Warm infused media to body temperature.
- For infants, use heated cribs and radiant heat sources.
Briefly: answers to topical questions
What pathophysiological mechanisms of thermoregulation are activated at the compensation stage in accidental hypothermia?
At the compensation stage in hypothermia, mechanisms aimed at increasing heat generation and reducing its loss by the body are activated.
- Behavioral regulation — leaving the cold environment, using clothing and heaters.
- Reduction of heat transfer efficiency — cessation of sweating and spasm of arterial vessels of the skin and muscles, which reduces peripheral circulation.
- Activation of heat production processes — stimulation of shivering (contractile thermogenesis) and activation of exothermic metabolic reactions (non-shivering thermogenesis), increased blood flow in internal organs.
- Initiation of the stress response — excitation of thermoregulation centers and neurohumoral activation involving the hypothalamus, pituitary gland, adrenal glands, and thyroid gland.
What is the pathogenesis of the development of internal organ edema in accidental hypothermia?
The pathogenesis of edema development in deep hypothermia is described for the decompensation stage and is associated with microcirculatory disorders.
This stage is characterized by slowing of blood flow up to stasis, an increase in blood shunting through arteriovenous shunts, a decrease in capillary blood filling, and an increase in vascular wall permeability. Against this background, tissue edema develops. Edema leads to an increase in blood viscosity (hemoconcentration), exacerbates microcirculatory disorders, and promotes the sludge phenomenon and thrombosis. Also, during deep hypothermia, local foci of ischemia form in tissues and organs.
What degrees (mild, moderate, severe) of accidental hypothermia are distinguished depending on the core body temperature?
Depending on the degree of internal body temperature drop, the WHO classification distinguishes three types (degrees) of hypothermia.
| Degree of hypothermia | Internal temperature | Skin temperature |
|---|---|---|
| Moderate | 36,4–36,0 °C | 35,9–35,5 °C |
| Moderate | 35,9–32,0 °C | 35,4–31,5 °C |
| Severe | ≤32,0 °C | ≤31,5 °C |
How to remember the three areas of pathogenetic therapy in hypothermia? Use the acronym ABC: Airway and circulation (APV, cardiac massage, BCC replenishment), Blood glucose (administration with insulin and vitamins), Cardinal acid-base state (buffer solutions and dextrans).
Class and exam questions
Why is active patient warming stopped at 33–34 °C?
Because the adequate function of the thermoregulation system is not restored immediately. If warming is continued, there is a high risk of developing hyperthermia.
Why is profound hypothermia used in surgery?
It is necessary for performing prolonged surgical manipulations on organs disconnected from blood flow. This method requires the use of a cardiopulmonary bypass machine, metabolic inhibitors, and the administration of muscle relaxants.
What are operations on "dry" organs?
These are interventions on the heart, brain, and other organs that require a significant reduction or complete temporary cessation of blood circulation in them.
What else to study on this topic
- Mechanisms of hyperthermia development during excessive patient warming
- Specifics of using dextrans (Polyglucin, Rheopolyglucin) for acid-base balance correction
- Techniques for warming internal organs via the stomach, lungs, and rectum
- Prevention of hypothermia in newborns: heated beds and radiant warmers
- Symptomatic management of frostbite against the background of general hypothermia
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