Mount Everest rises 8,849 metres above sea level. Its uppermost slopes lie in a region mountaineers rightly call the death zone. At approximately 8,000 metres and above, atmospheric pressure is so low that the human body can no longer acclimatise sufficiently to survive for long.
Air pressure at this height is little more than one-third of that at sea level. Although oxygen still makes up approximately 21% of the atmosphere, each breath contains far fewer oxygen molecules, so much less oxygen passes from the lungs into the bloodstream. A climber may remain conscious, continue upwards and even reach the summit, but the body is steadily deteriorating. The longer someone remains there, the greater the danger.
There are times when emotional, physical or psychological stress can push us into a personal danger zone. The basic supports that maintain our well-being may begin to fail, and our condition can deteriorate surprisingly quickly. It is important to recognise the warning signals and respond promptly. The longer we remain in such a place, the more difficult recovery may become.
What the Death Zone Does to the Body
The shortage of oxygen places the body under extraordinary strain. Researchers who took arterial blood samples from four climbers breathing ambient air at 8,400 metres found an average arterial oxygen pressure of only 24.6 mmHg—an extraordinarily low value, close to the limits of human tolerance. To compensate, climbers breathe faster and more deeply, their heart rate rises and the circulation works harder to deliver the available oxygen to vital organs.
Even the ordinary tasks of life can sometimes demand almost superhuman effort. When we must operate at full capacity merely to stand still, strain accumulates. That is itself a warning sign worth recognising.
The Brain Becomes Slow and Unreliable
The brain is particularly sensitive to a lack of oxygen. Although it makes up only about 2% of body weight, it consumes approximately 20% of the body’s oxygen while we are resting. Weight for weight, brain tissue uses roughly ten times more oxygen than the average body tissue.
At extreme altitude, oxygen deprivation causes thinking to slow, memory and coordination to deteriorate and judgement to become dangerously poor. A climber may feel oddly confident while making irrational decisions. He or she may forget to attach to a safety line, misread the route, ignore a turnaround time or insist on continuing when descent is essential.
This is one of the cruellest features of the death zone: the very organ needed to recognise danger is itself being impaired. Exhaustion, sleep deprivation, cold and dehydration make the problem worse. In our own danger zones, our ability to assess the situation clearly may be among the first things affected. We can react impulsively or, while trying to improve matters, make them worse. That is why it is important to recognise our limits before judgement becomes clouded—and to listen to people we trust.
High-Altitude Cerebral Oedema: Swelling of the Brain
Altitude illness can progress to high-altitude cerebral oedema (HACE), a dangerous swelling of the brain. Early signs include confusion, unusual behaviour and loss of balance. A person who cannot walk heel-to-toe in a straight line may already be gravely ill. Without immediate descent and treatment, HACE can progress rapidly to coma and death.
Escaping a crisis requires thought and sensible decisions. If our ability to think clearly is itself impaired, however, we may no longer be able to find the way out without help.
The Lungs Begin to Fill with Fluid
When oxygen is already desperately scarce, low oxygen levels can cause the small arteries in the lungs to constrict. This narrowing is often uneven, forcing too much blood through the vessels that remain relatively open. The resulting pressure can damage their delicate walls, allowing fluid to leak from the capillaries into the surrounding tissue and eventually into the air sacs.
The fluid occupies space that should contain air and makes the lungs stiffer, so still less oxygen can cross into the blood. Falling oxygen levels produce further constriction and leakage, creating a dangerous vicious circle. This is high-altitude pulmonary oedema (HAPE).
A climber may become breathless even while resting, develop a cough, experience overwhelming weakness or become unable to keep pace. Breathing may become noisy, and crackling sounds can develop in the lungs. In advanced cases, the person may cough up pink or blood-tinged frothy sputum. The lungs that are desperately needed to collect oxygen are becoming progressively less able to do so. HAPE can worsen with frightening speed.
In severe HAPE, a person is effectively suffocating as fluid fills spaces that should contain air. In life, too, we can become so focused on external pressures that we fail to notice the internal damage they are causing. Trusted people around us may recognise the warning signs before we can and help us obtain the support we need.
The Body Consumes Itself
Appetite commonly fades at great altitude, while digestion becomes more difficult and the energy cost of climbing remains enormous. Climbers lose weight, fat and—particularly above approximately 5,000 metres—muscle. The body begins breaking down its own tissues at precisely the time when the climber needs exceptional strength to descend.
Dehydration is another constant danger. Cold, dry air increases water loss through rapid breathing, while exertion causes further losses. Yet melting snow and drinking require time and fuel. Dehydration reduces plasma volume, concentrates the blood and compounds fatigue and circulatory strain.
We can become so devoted to a goal or task that we remain blind to its consequences. Losing our appetite, motivation, sleep or ability to attend to basic needs can signal a serious imbalance. We need the essentials that sustain us: nourishment and rest, good friends, close family, a safe home and a path forward.
Cold Becomes Harder to Resist
The death zone combines oxygen starvation with extreme cold and fierce winds. As exhaustion and dehydration grow, the body becomes less capable of producing and preserving heat.
Blood vessels in the hands and feet constrict as the body tries to protect the heart and brain, greatly increasing the risk of frostbite. Low oxygen also impairs judgement, so a climber may fail to notice a freezing hand, a loose glove or the first signs of hypothermia.
We sometimes endure hardship while overlooking the damage it is doing. What is lost may not be a finger or toe, but our peace of mind, sense of self or ability to manage everyday life. We should regularly ask whether our body, mind and spirit are being sustained. Neglect is neither fair to ourselves nor to those around us.
Acclimatisation: Teaching the Body to Survive on Less
Acclimatisation is the gradual process by which the body adjusts to falling oxygen pressure. Within minutes of reaching altitude, breathing and heart rate increase. Over the following days, the kidneys excrete bicarbonate, allowing the body to sustain the rapid breathing needed to obtain more oxygen. The fluid portion of the blood also decreases, concentrating its haemoglobin. Over a longer period, increased erythropoietin stimulates the production of additional red blood cells, improving the blood’s oxygen-carrying capacity.
These changes help, but they do not restore sea-level performance. Physical fitness is essential for climbing, yet even an exceptionally fit athlete can develop altitude illness. Fitness and acclimatisation are not the same thing. The purpose of acclimatisation is not to make the death zone safe. It is to reach it in the strongest and best-acclimatised condition possible, spend as little time there as practicable and descend promptly.
Recovery from periods of intense stress also requires genuine breaks from the pressure—the equivalent of returning to base camp to recover. This may mean seeking the right company, de-escalating a situation, speaking to a professional or creating some distance from whatever is causing the strain. We may eventually have to re-enter the fray, but a period of recovery can rebuild surprising reserves of strength. On Everest, courage does not always mean continuing upwards. Sometimes it means possessing the wisdom to descend before conditions take away the ability to choose. The same can be true in life.
