(and, indeed, other 8,000ers)
A human can survive for weeks without food and only days without water but we can merely survive for minutes without oxygen.
As you go to even moderate altitudes the air gets ‘thinner’. At around 5,500 metres there is half the amount of air that you would find at sea level. Despite there being less air it is still made up of around 21% Oxygen, 75% Nitrogen and 3% (and rising) Carbon Dioxide (plus a small fraction of other gases).
When you consider that humans are not designed to live at altitude it is amazing that the body does actually have a few mechanisms to compensate for the rarefied atmosphere. Some of the mechanisms initially have slightly detrimental side effects but they are soon evened out by other adjustments (there is more altitude information elsewhere about acclimatisation / AMS / HACE / HAPE etc).
For most people these effects will first become evident at around 3,500m (for a few it becomes noticeable at as little as 2,500m). One of the first things that people notice is that they become breathless far more easily than at sea level. If you were to monitor pulse and breathing rates you would find that both are elevated – this is the body’s way of compensating for there being less oxygen available. By breathing more, and by pumping the blood faster, the body can rectify the apparent shortfall.
Importantly, red blood cell production increases (after a few weeks), resulting in an increased haemoglobin concentration, which is required to pick up oxygen and transport it around the body. All these mechanisms enable the body to continue to deliver enough oxygen to each cell, despite the lower oxygen levels. At sea level our blood is 98-99% saturated with oxygen and this decreases to typically 89-90% at 3000m and reaches as low as 40% on the summit of Everest.
If you were to keep ascending, steadily increasing your sleeping altitude every day, eventually your body would not be able to keep up with the ever decreasing oxygen supply, you would become extremely ill and debilitated from hypoxia (inadequate oxygen levels) and would either have to abort your trip or you would die.
Hypoxia has progressive effects on the functioning of the central nervous system. Accidents that occur at extreme altitude on Everest, and other mountains, may be due to poor judgment as a consequence of hypoxic depression of cerebral function. There will be other factors that also contribute to accidents, but whatever it is that has happened, being hypoxic can’t help the situation.
At extreme altitude supplementary oxygen can be used to prevent or reduce the effects of severe hypoxia. Having said that, it needs to be used in conjunction with a sensible acclimatisation schedule. Everest has rarely been climbed without oxygen and most climbers use bottled oxygen above 7,000m on an 8,000m peak. However, it is bulky and expensive so flow rates are kept low. When sleeping, a typical flow rate of 0.5 to 1 litre / min is delivered via a face mask, and when climbing above 8,000m this is increased to 2 to 3 l/min.
Typically a cylinder weighs in at around 2.5 / 3.5kg for a 3 / 4 litre bottle (or as much as 7kg for a 5.5 litre bottle). Depending on the flow rate they can provide oxygen from as much as 15 hours (or more) down to only a couple (or less). Typically the oxygen is delivered via a regulator on a constant flow so it is important to match the flow rate to your pace and vice versa.
Oxygen is delivered to the mask at a constant flow adjusted by a regulator. While the climber breathes out the constant flow oxygen is diverted to an accumulator. When an inhalation is made the accumulated oxygen is delivered as the first part of the breath, deep into the lungs. The rich oxygen mix is the first part of the breath until the accumulator empties then a secondary valve opens to allow ambient air to complete the filling of the anatomical dead space (the pipe feeding the deep lung where no oxygen exchange can take place).
A demand fed system has been developed that detects the pressure differential and delivers a precise squirt of oxygen via tubes up the nose every time the climber breathes in. However, on Everest in 2005, they had an 80% system failure rate and recommended that climbers revert to a regular constant flow system. It will be a great breakthrough if the tolerances can be achieved that will cope with the demanding atmosphere (or lack of it) of extreme altitude mountaineering. But it is not a failsafe redundant system which is what is necessary on the likes of Everest.
There will always be a debate as to whether oxygen should be used for ultra high altitude mountaineering. There are very, very few people who have summited Everest without oxygen and undoubtedly, whilst oxygen allows people to venture to extreme altitude, there would be many more deaths if it wasn’t used. Whether or not it is viewed as being ethical, it is undoubtedly sensible. After all, a client who becomes debilitated puts the lives of other climbers, and the Climbing Sherpas, at risk.
• Become totally acquainted with your system before you have to use it
• Make sure you know which goggles, glasses, hats and balaclavas work well with your mask
• Make sure you can change bottles without cross threading the regulator
• Be aware that frozen condensation from your breath can clog the outlet valve
• You can’t adjust the regulator without removing your rucksack so set the rate (not too high) and match your pace accordingly. You can always turn it up later (or get someone reliable to do it for you).
• But be aware that some of the older regulators adjust in exactly the opposite direction so if someone is adjusting the flow rate for you they will be turning your flow rate up instead of down.
• There is no substitute for being acquainted with your system so practise practise practise. Preferrably before you put it on for the first time at Camp 3!