Hunting and Wildlife Magazine - Issue 225 - Winter 2024
Words By: Simon Carkeek, PracMed NZ.
Many understand that when hunters and adventurers are exposed to the often-harsh extremes of New Zealand’s outdoors, there is an inherent risk of hypothermia in the colder months. While environmental hypothermia is somewhat well-known, other forms can be especially pertinent to hunters. This condition, often underestimated, can sneak up silently on hunters and outdoor enthusiasts, turning a routine trip into a survival challenge. Understanding the causes, recognising the symptoms, and managing hypothermia effectively is crucial, whether navigating the dense bush of Fiordland or the alpine terrains of the Southern Alps. In this article, we delve into the critical aspects of hypothermia, providing you with the knowledge to stay safe and warm in the wild.
What is Hypothermia?
Hypothermia, a critical medical emergency, occurs when the body loses heat faster than it can generate it, leading to a dangerously low body temperature. This life-threatening condition can result from prolonged exposure to cold environments or as a serious and often underestimated complication of significant blood or fluid loss. Effective management strategies vary significantly based on the cause, emphasising the need for tailored approaches to manage hypothermia in the outdoors.
Hypothermia can be broken into two categories:
- Mild Hypothermia: core body temperature below 35°C. Symptoms include shivering, survival mode (self-preservation behaviour), mild disorientation such as stumbling, and complaints of tiredness.
- Moderate/Severe Hypothermia: core temperature below 32°C. This stage is marked by the absence of shivering, inexplicable removal of clothing, unwillingness to move or get up, slurred or incomprehensible speech, and/or significant disorientation.
For effective function of the vital organs, such as the heart, brain and lungs, the body’s core temperature typically hovers around 36.6ºC. When this core temperature drops significantly, it stresses the vital organs, which can begin to fail, potentially leading to death.
In general, there are two primary causes of hypothermia:
- Environmental Hypothermia - caused by prolonged exposure to cold conditions.
- Hypovolemic Hypothermia - caused by severe fluid loss.
What are the differences?
Environmental Hypothermia
Environmental hypothermia occurs when the body is exposed to cold temperatures for a prolonged period. It can occur during outdoor activities such as hunting, tramping, skiing or camping.
Contributing risk factors are:
- Inadequate clothing - such as cotton and cotton blends (Synthetics and wool are optimal for a base layer).
- Prolonged exposure to windy and/or wet conditions.
- Immersion in cold water.
While all cases of hypothermia must be treated as a medical emergency, survival from environmental hypothermia has been recorded with a patient with a core temperature as low as 13.7°C.
Hypothermia from Blood/Fluid Loss:
The lesser known of the two causes, hypothermia, can also result from severe blood or fluid loss.
Common mechanisms include:
- Serious/prolonged bleeding.
- Medical conditions such as sepsis.
When hypothermia results from severe blood loss, the impact on the body is both immediate and critical. To understand this, it’s helpful to compare two types of physical activity: sprinting (anaerobic) versus walking (aerobic).
Normally, our body operates aerobically – like walking – using oxygen to fuel our cells. However, significant blood loss disrupts this by reducing the body’s core temperature, reducing its ability to use oxygen effectively. For every degree Celsius lost, about 10-15% of the blood's clotting abilities are diminished. As the body cools and loses its ability to clot blood, it switches to an anaerobic (like sprinting) metabolism, which doesn't require oxygen but produces energy less efficiently and creates acidic by-products.
This switch is problematic because acidic blood further impairs heart function, causing a dangerous feedback loop that accelerates the body's cooling. This scenario is part of what’s known as the lethal triad in medical emergencies: hypothermia, coagulopathy (the inability to clot blood), and metabolic acidosis (excess acidity in the blood).
In this state, just like a sprinter who can't sustain a sprint for as long as they can walk, the body cannot sustain its vital functions without adequate heat and oxygen. There have been no recorded cases of survival once the core body temperature drops below 32ºC in hypovolemic hypothermia (compared with 13.7ºC in environmental hypothermia), emphasising the need for urgent and aggressive intervention to manage this type of hypothermia. Unlike environmentally induced hypothermia, which might develop more slowly and can often be managed with gradual warming, hypothermia from blood loss requires swift, decisive action to address these cascading physiological changes.
So, what can we do?
When addressing hypothermia, understanding the four mechanisms of heat loss is crucial:
- Conduction: heat is transferred from the skin to the surrounding air.
- Convection: heat is lost to moving air.
- Radiation: heat radiates from the body into the environment.
- Evaporation: heat is lost as water (sweat) evaporates from the skin.
Management of Hypothermia
- Insulate from the ground: place a thermal barrier between the casualty and the ground to prevent heat loss by conduction.
- Minimise airflow: wrap the casualty properly to reduce air movement around the body, which addresses convection.
- Dry clothing: remove wet or blood-soaked clothing to prevent heat loss through evaporation and conduction.
- Rewarming techniques: use passive (with body heat and reflective materials) and purpose-made rewarming strategies.
For Environmental Hypothermia:
- Warm beverages: offer a warm, high-energy drink like hot chocolate to support the metabolic demands of shivering.
- Emergency gear: carry an emergency survival bag as a standard item for immediate insulation and shelter. Note that a commonly purchased single-layer emergency blanket (usually silver or gold) is insufficient to significantly impact hypothermia. Investing in quality gear, such as a two or three-layer Blizzard blanket, is recommended. When it comes to life-saving interventions, having the right equipment at hand when it matters is critical. These lightweight, rugged, two or three-layer blankets are a must-have in every hunter's or tramper’s pack.
In wilderness settings:
- Natural insulation: use materials like tussock, moss, and dry leaves to create a base layer for insulation. Avoid direct contact with wet materials.
- Improvised shelter: construct shelter using natural features and carried items, being mindful of water hazards in adverse weather conditions.
- Group awareness: remember, if one person is hypothermic, others may be at risk too. Prioritise shelter and address heat loss collectively.
Key takeaways:
- Prompt action: hypothermia demands quick recognition and immediate warming measures.
- Medical assistance: seek professional help urgently while initiating warming measures.
- Preparation and prevention: regular gear checks and carrying emergency supplies like Blizzard bags and trauma kits can significantly enhance safety and comfort in outdoor settings.
Make sure you are prepared and aware of hypothermia risks to enhance survival and comfort during your outdoor adventures. Ensuring gear checks have been completed may seem over the top, but when things go sideways, things like Blizzard bags and emergency trauma kits make a huge difference in not only a casualty's comfort but also, potentially, their survival.
Stay safe and be thoroughly prepared for the unexpected.
However, significant blood loss disrupts this due to reduced circulation (caused by a drop in blood volume), reducing the amount of oxygen available. The by-product is a reliance on sugar as a primary source of energy, causing the blood to become acidic, decreasing the heart's ability to function, and decreasing core temperature.
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