Accidental Hypothermia - Stages, Pathophysiology, Symptoms, Diagnosis, and Management

Introduction:

Hypothermia refers to a condition in which the body’s temperature falls below the minimum temperature range. The rate of losing the heat is faster than the heat produced and results in an emergency condition. Accidental hypothermia in a healthy person can occur by getting exposure to a cold environment, leading to primary accidental hypothermia, or triggered by other conditions like illness, intoxication, or trauma, leading to secondary hypothermia.

What Are the Stages of Accidental Hypothermia?

Hypothermia is classified based on the manifestation of clinical signs and symptoms, which are as follows:

1. Cold Stress – This is not an actual hypothermic state. The patient will have normal mental status and presents with shivering symptoms. Normal body functioning is not affected, and can take care of themselves. The core temperature will be 35 to 37°C (95 to 98.6°F).

2. Mild Hypothermia – The patient will be alert, with altered mental status. Shivering will be present. Cannot perform their functions normally and fail to take care of themselves. The core temperature will be 32 to 35°C (90 to 95°F).

3. Moderate Hypothermia – The patient presents with a decreased level of consciousness and sometimes can be unconscious, too. Shivering may or may not be present. The core temperature is 28 to 32°C (82 to 90°F).

4. Severe/Profound Hypothermia – The patient will be unconscious. Shivering will be absent. The core temperature will be below 28°C (below 82°F).

What Happens When One Reaches the Hypothermic State?

• This heat is generated in the human body by the mechanism of cellular metabolism (most commonly attributed to the heart and liver), and the excess heat is lost from the body through the skin and lungs.

• The normal human core temperature is 37±0.5°C. With the help of autonomic mechanisms, the human body maintains this temperature to regulate heat loss and gain. However, the human body has a limited physiologic capacity to respond to cold environmental conditions and to adapt accordingly. Hence, behavioral modifications like clothing and shelter are crucial to fight against hypothermia.

• In response to cold stress, the hypothalamus stimulates heat production by shivering and increases thyroid, catecholamine, and adrenal activities, which in turn causes sympathetic vasoconstriction, minimizing the rate of heat loss from the body by reducing blood flow to peripheral tissues (where cooling is greatest).

• The generalized cooling decreases tissue metabolism and inhibits neural activity.

• Once the core temperature reaches 32°C, metabolism, ventilation, and cardiac output begin to decrease, and shivering becomes less effective and finally stops as there is a gradual drop in the core temperature.

What Are the Clinical Symptoms of Accidental Hypothermia?

As the condition progresses, the patients present with respective clinical signs and symptoms, which include,

Mild Hypothermia: Presents as,

• Tachypnea (faster and shallow breathing).

• Tachycardia (increased heart rate).

• Initial hyperventilation.

• Ataxia (altered muscular coordination/moments)

• Dysarthria (difficulty in speaking).

• Impaired judgment.

• Shivering.

• Cold diuresis (decreased body temperature causing increased urination)

Moderate Hypothermia: Is associated with:

• Reduced pulse rate and cardiac output.

• Hypoventilation.

• Central nervous system depression.

• Hyporeflexia (reduced muscle response to external stimuli).

• Decreased renal blood flow.

• Loss of shivering.

• Atrial fibrillation (irregular heart rhythm).

• Junctional bradycardia (heart rate below 40 beats per minute at the atrioventricular junction).

• Depressed pupillary light reflex.

• Dilated pupils are seen below a core temperature of approximately 29°C.

Severe Hypothermia: Manifests as,

• Pulmonary edema.

• Oliguria (decreased urine output).

• Areflexia (absence of muscle response to external stimuli).

• Coma.

• Hypotension.

• Bradycardia (decreased heart rate).

• Ventricular arrhythmias (irregular heartbeat arising from the ventricles) include ventricular fibrillation (irregular heart rhythm) and asystole (a type of cardiac arrest).

• Loss of corneal and oculocephalic reflexes (loss of eye and head reflex).

How Is Accidental Hypothermia Diagnosed?

Accidental hypothermia can be diagnosed by various methods:

Temperature Measurement:

• Rectal temperature can be employed in conscious patients.

• In patients with severe hypothermia, especially in cases of endotracheal intubation, an esophageal probe is inserted that provides a near approximation of cardiac temperature.

• Esophageal temperature is the most accurate method to track the progress of rewarming.

• Bladder temperatures are commonly used and are adequate in mild to moderate hypothermia. However, bladder and rectal temperatures should not be used in critical patients during rewarming.

Laboratory Studies: Laboratory studies should be assessed to identify any potential complications and comorbidities, including lactic acidosis, rhabdomyolysis degeneration of the muscle), bleeding diathesis, and infection. The following tests are required in moderate and severe cases of hypothermia:

• Fingerstick glucose.

• Electrocardiogram (ECG).

• Basic serum electrolytes, including potassium and calcium.

• Blood urea nitrogen (BUN) and creatinine.

• Serum hemoglobin, white blood cell, and platelet counts.

• Serum lactate.

• Fibrinogen.

• Creatine kinase (CK).

• Lipase.

• Arterial blood gas in ventilated patients.

• Chest radiograph.

How Is Accidental Hypothermia Treated?

Resuscitation:

• In patients with respiratory distress or those who cannot maintain a patent airway, endotracheal intubation is performed.

• Early intubation can help in clearing the secretions produced by cold-induced bronchorrhea and in patients with altered mental status or a decreased cough reflex.

Cardiopulmonary Resuscitation:

• Cardiopulmonary resuscitation (CPR) includes chest compressions and should be carried out in patients with accidental hypothermia who develop cardiac arrest.

• Contraindications to chest compressions include verified DNR (do not resuscitate) status patients (who have undergone lethal injuries and a frozen chest wall that is not compressible).

• CPR should be started immediately if the pulse is not evident even after checking for one minute.

• CPR can be delayed up to ten minutes only if continuous CPR is not possible.

• In a patient with a core temperature of 20 to 28°C, or if the core temperature is not known, CPR can be attempted for at least five minutes, alternating with periods without CPR, no longer than five minutes.

• In patients with a core temperature below 20°C, CPR should be given continuously for periods of at least five minutes, alternating with periods of no CPR for no longer than ten minutes.

Fluid Resuscitation:

• Patients with moderate or severe hypothermia end up being hypotensive during rewarming owing to severe dehydration and fluid shifts.

• Two large (14- or 16-gauge) peripheral IV (intravenous) lines should be placed. Blood pressure is normalized by warm (40 to 42°C) infusions of Isotonic crystalloid. Large infusions may be required.

• Intraosseous (IO) access may be easier than IV access in patients with vasoconstriction.

• IO lines should be used with a 10 mL bolus of isotonic crystalloid with or without Lidocaine immediately after insertion to open the marrow space and to ensure good flow.

• Temporary placement of a femoral venous catheter is preferred to avoid arrhythmias resulting from irritation of the right atrium.

• Norepinephrine should be used to maintain blood pressure in cases that did not recover with fluid resuscitation.

Rewarming Interventions:

Rewarming techniques are classified into:

• Passive External Rewarming: Passive external rewarming is indicated in mild hypothermia cases and can also be used in patients undergoing aggressive rewarming for moderate to severe hypothermia. After wet clothing is removed, the patient is covered with blankets or other types of insulation, causing passive external rewarming and also aiding in intrinsic heat production. Passive external rewarming requires physiologic reserve sufficient to generate heat by shivering or by increasing the metabolic rate and is unsuccessful in severe cases of glycogen depletion, sepsis, or hypovolemia, especially in older adult patients. Many older adult patients lack normal metabolic and cardiovascular homeostasis and require active rewarming.

• Active External Rewarming: A combination of warm blankets, heating pads, radiant heat, warm baths, or forced warm air is applied directly to the patient's skin in active external rewarming. These methods are indicated in moderate to severe hypothermia (<32°C) cases and for patients with mild hypothermia who lack physiologic reserve.

• Active Internal Core Rewarming: Active internal rewarming is also called active core rewarming. It is the most aggressive strategy and can be used alone or combined with active external rewarming in patients with severe hypothermia (<28°C) or patients with moderate hypothermia who fail to respond to less aggressive measures. Endovascular rewarming is the method of choice for patients not requiring ECLS (extracorporeal life support) or if ECLS is not available. Endovascular temperature control catheters are widely available. If not available, alternative rewarming methods like irrigating the peritoneum or the thorax (through the pleural space) with warmed isotonic crystalloid are employed.

• ECLS (Extracorporeal Life Support): Hypothermic patients with asystole can be rewarmed with ECLS until the irritated myocardium resumes electrical activity (usually around 28 to 30°C), with shockable rhythm defibrillation being required to achieve the return of spontaneous circulations.

Conclusion:

The management of hypothermia involves the evaluation of the airway, breathing, and circulation, preventing further heat loss, and initiating the rewarming process appropriate to the degree of hypothermia. Based on additional clinical experiences, management guidelines, and documentation, the treatment of accidental hypothermia has been redefined. ECLS has substantially improved survival and is the treatment of choice for patients with unstable circulation or cardiac arrest.