What Body System Is Affected by Hypothermia?

October 1, 2025 •

4 min read

Hypothermia, defined as a core body temperature below 95°F (35°C), affects virtually all organ systems. While the entire body is impacted, it particularly takes a toll on the cardiovascular, nervous, and respiratory systems, leading to a cascade of life-threatening complications if left untreated.

Quick Summary

Hypothermia severely impacts the cardiovascular, nervous, respiratory, and metabolic systems, causing slowed heart rate, confusion, and depressed breathing, which can lead to organ failure and death.

Key Points

Multiple Systems Affected: Hypothermia is a multi-systemic issue, with the heart, brain, and lungs being particularly vulnerable.
Cardiovascular Slowdown: A falling core temperature leads to decreased heart rate and cardiac output, increasing the risk of life-threatening arrhythmias and cardiac arrest.
Central Nervous System (CNS) Depression: The nervous system slows down, causing confusion, impaired judgment, and eventually, a coma.
Respiratory Failure: Breathing becomes slow and shallow, leading to decreased oxygen intake and a potentially dangerous buildup of carbon dioxide.
Metabolic Collapse: The body's metabolic processes falter, resulting in a dangerous drop in energy production and severe electrolyte and acid-base imbalances.
Paradoxical Undressing: Severe hypothermia can cause confusion so profound that individuals may irrationally remove their clothing, accelerating heat loss.
Severity Determines Effect: The signs and severity of hypothermia vary greatly depending on the core body temperature, progressing from shivering and confusion to unconsciousness and organ failure.
Requires Immediate Treatment: Any suspected hypothermia is a medical emergency requiring immediate, and often advanced, medical care to rewarm the body and stabilize vital functions.

The Body's Reaction to Cold

When the body is exposed to cold, it first initiates a series of involuntary responses to conserve and generate heat. Shivering, the rapid contraction of skeletal muscles, generates heat, while peripheral vasoconstriction—the narrowing of blood vessels in the extremities—reduces heat loss from the skin. These protective mechanisms work effectively in mild cold. However, when exposure is prolonged or severe, the body's ability to maintain a stable core temperature is overwhelmed, and hypothermia ensues. As the core temperature drops, all physiological functions begin to slow down.

The Impact on the Cardiovascular System

The cardiovascular system is one of the most significantly affected by hypothermia, with its functions progressively deteriorating as body temperature falls. The initial response involves peripheral vasoconstriction to redirect warm blood to the body's core, but this also increases the heart's workload. As the condition worsens, the heart rate (bradycardia) and cardiac output decrease. This is followed by a cascade of electrical abnormalities. The cardiac pacemaker cells' depolarization slows, which can lead to various arrhythmias, with atrial fibrillation and ventricular fibrillation being common in severe hypothermia. In extreme cases, the heart can become irritable, and vigorous movements or attempts at rewarming can trigger fatal ventricular fibrillation. The ultimate risk is cardiac arrest, the final stage of failure for this critical system.

Effects on the Nervous System

The central nervous system (CNS) is highly sensitive to temperature changes and experiences progressive depression during hypothermia. This depression impairs coordination and judgment, which can lead to dangerous behaviors, such as the confusion that causes paradoxical undressing in some victims. As body temperature continues to drop, mental acuity diminishes further, progressing from confusion and lethargy to stupor and eventually a coma. Other neurological signs include:

Slurred speech or mumbling
Clumsiness or poor coordination
Memory loss
Fixed and dilated pupils in severe cases
The cessation of shivering, which typically stops when core temperature falls below 89.6°F (32°C)

The slowing of brain electrical activity can become so profound that an electroencephalogram (EEG) may resemble brain death in profound hypothermia.

The Respiratory System Under Cold Stress

The respiratory system also slows down significantly in response to decreasing body temperature. This includes a decrease in both the rate and depth of breathing (bradypnea). This reduced ventilation can cause an accumulation of carbon dioxide ($CO_2$) in the blood, leading to respiratory acidosis. Additionally, the body's protective mechanisms, such as the cough reflex and the ciliary activity that clears the airways, become suppressed. These effects increase the risk of aspiration and pneumonia, compounding the already serious condition. In moderate to severe hypothermia, the respiratory rate can drop to just a few breaths per minute.

Metabolic Changes During Hypothermia

Hypothermia disrupts the body's metabolic processes, impacting multiple organ functions. The metabolic rate, or the speed at which the body converts stored energy into heat, decreases significantly. For every 1°C drop in core temperature, the metabolic rate decreases by 5–8%. This metabolic slowdown is initially a protective mechanism but can quickly become detrimental. Key metabolic effects include:

Acidosis: The body shifts towards anaerobic metabolism, producing excess lactic acid, which, combined with the liver's impaired ability to process it, leads to metabolic acidosis.
Electrolyte imbalances: Electrolyte abnormalities, such as hyperkalemia, can occur and further destabilize the heart.
Glucose metabolism: Glucose utilization decreases, insulin release is inhibited, and glucose production from the liver increases, potentially leading to hyperglycemia in the initial stages.

Comparison of Systemic Effects at Different Hypothermia Stages


Feature	Mild Hypothermia (95°F - 89.7°F / 35°C - 32°C)	Moderate Hypothermia (89.6°F - 82.4°F / 32°C - 28°C)	Severe Hypothermia (< 82.4°F / < 28°C)
Cardiovascular	Peripheral vasoconstriction, increased heart rate (tachycardia) initially.	Slowed heart rate (bradycardia), cardiac dysrhythmias (e.g., atrial fibrillation).	Severe hypotension, severe bradycardia, increased risk of ventricular fibrillation or asystole.
Nervous System	Shivering, confusion, impaired coordination and judgment.	Stupor, cessation of shivering, paradoxical undressing.	Coma, unreactive pupils, absent reflexes, EEG resembling brain death.
Respiratory System	Increased respiratory rate (tachypnea).	Decreased ventilation rate, respiratory depression.	Severe bradypnea, severe respiratory acidosis.
Metabolic System	Increased metabolic rate (due to shivering), cold diuresis.	Decreased metabolic rate, hyporeflexia, coagulopathies.	Hyperkalemia, metabolic acidosis from tissue anoxia.

Emergency Intervention

Because hypothermia affects multiple body systems, emergency intervention requires a coordinated approach. Treatment depends on the severity of the hypothermia. For mild cases, passive rewarming using blankets and a warm environment may be sufficient. For moderate to severe cases, active rewarming is necessary and can include techniques like warm intravenous fluids, warmed and humidified oxygen, and external rewarming systems. In the most severe cases, invasive procedures such as extracorporeal blood rewarming (ECR) may be required to rapidly warm the core. The American Heart Association provides guidelines for managing hypothermic cardiac arrest, emphasizing gentle handling and continued CPR during resuscitation. A key aspect of treatment is to protect the patient from further heat loss by removing wet clothing and insulating them.

Conclusion: The Domino Effect of Cold

Hypothermia's multi-systemic effects create a domino effect of physiological collapse, with a cooling core temperature leading to a progressive slowdown of the body's most critical functions. The cardiovascular system's failure to maintain adequate circulation, combined with the nervous system's inability to regulate body temperature and consciousness, creates a lethal positive feedback loop. When coupled with respiratory and metabolic compromise, the body's entire regulatory network breaks down, making timely recognition and treatment critical for survival. Understanding that hypothermia impacts the body as a whole, rather than just causing localized cold injury, is essential for effective emergency response and prevention. For detailed medical protocols, please consult authoritative sources like the American Heart Association.

Frequently Asked Questions

The thermoregulatory center in the nervous system is the first to respond to a drop in body temperature by initiating protective measures like shivering and peripheral vasoconstriction to conserve heat.

If recognized and treated promptly, mild hypothermia often has no long-term effects. However, severe or prolonged hypothermia can cause permanent damage to the heart, brain, kidneys, and other organs due to oxygen deprivation and cell death.

Common symptoms of mild hypothermia include shivering, confusion, impaired judgment, and fumbling hands. Shivering is the body's automatic defense to generate heat.

Mild hypothermia can be treated at home by moving to a warm, dry place, removing wet clothing, and using dry blankets. However, any signs of moderate or severe hypothermia, such as slurred speech or confusion, warrant immediate medical attention.

In severe hypothermia, the nervous system's ability to regulate body temperature breaks down, causing the shivering reflex to cease. This is a sign that the body is losing its fight against the cold and is a critical warning sign.

Severe hypothermia requires active core rewarming in a hospital setting. This may involve using heated intravenous fluids, warm humidified oxygen, or advanced invasive techniques like extracorporeal blood warming to raise the core temperature.

No, hypothermia can occur in cool temperatures (above 40°F) if a person is wet from rain, sweat, or submersion in water, as wet skin loses heat much faster than dry skin.