Archive for the ‘Acclimatisation myths’ Category

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Water Myth , Revisited

January 7, 2011

Straight quote from a recent altitude sickness discussion thread on the Thorntre, from frequent Nepali trekker tomtraveller :

“keep drinking the water, and don’t stop drinking lots the entire time you are at high altitude”
vistet adds “The difference between health and poison is , as in many other cases , a dose question …Pushing large volumes of water only leads to electrolyte imbalance…Taken far enough it can lead to death in cerebral and general edema “

Last fall while trekking Langtang, I met a Norwegian trip leader who was dealing with a very ill trip member. The ill trekker had been experiencing symptom similar, yet different to cerebral edema. Porters carried her down several thousand vertical feet, but her condition did not improve. She was in and out of consciousness. The guide called for a helio evacuation, but the chopper couldn’t arrive until the next morning because of weather conditions. The ill women was placed in a Gamow bag for the night and the trip leader described how difficult it was to keep the bag inflated properly all night, even with a team of people. She was unconscious when she was flown back to Kathmandu and she was in a coma for several days. It turns out that she had drank copious amounts of water, as vistet describes, and she had severely messed up her electrolyte balance. She recovered, and now is ok. But what vistet describes can happen. You need to stay hydrated, but not overly so.

On the less anecdotal side : there are actually a few studies that have gone in the relation between fluid balance and AMS. The Journal of Applied Physiology published a study in 2004 : Early fluid retention and severe acute mountain sickness . The most notable results : the AMS group was the group with lowest urine output , a positive fluid balance and the highest levels of antidiuretic hormone. The non-AMS group was the one with a negative fluid balance , highest urine output and lowest levels of antidiuretic hormone :

“Antidiuretic hormone fell in non-AMS and rose in AMS within 90 min of exposure and continued to rise in AMS, closely associated with severity of symptoms and fluid retention.”

“The extra fluid consumed by both groups just before ascent was rapidly eliminated in non-AMS,.., however, in AMS the elimination of this extra load did not take place.”

Another more practically targeted article in Clinical Journal of Sport Medicine , Exercise Associated Hyponatremia Masquerading as Acute Mountain Sickness , raises the question of how many get sick not in spite of precautions but because of them :

“Vigorous hydration is an unproven yet widely favored maneuver to prevent AMS. Hikers are known to drink copious amounts of fluids until they produce gin clear urine. This is both an unphysiologic and unsafe practice.. In all likelihood, a significant number of hikers and skiers are developing encephalopathy at high altitude with EAH, yet the hyponatremic encephalopathy component of their condition is going unrecognized..”

“Serum sodium below 136 mEq/L should be viewed as abnormal and as a contributing factor to AMS. EAH should be considered the primary cause of encephalopathy if the serum sodium is less than 130 or if symptoms are not improving with conventional therapy”

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Acclimatisation myth # 3 : The healing water

May 12, 2007

Water. Lots of water. If there is one thing you´ll hear again and again , it´s the importance of drinking . A lot.

“I havent peed that much since I was in diapers”

“one litre for every thousand meters..”

Some go on to mention other aspects of fluid balance : thin , clear urine is a good thing , so is a high urine output.

There are some funny aspects , though  : this maxim is for one thing never repeated by medically trained .

The end results of altitude sickness are called edema : excess of fluid in the tissues , mainly the brain and lungs. So this is a way of preventing accumulation of fluids in one place , by pouring in more of it in another.

If you find this hard to folllow , join the club.

The basics of fluid balance are exactly this complex : what goes in up here (the mouth) must come out down here (your urinary outlet of choice) . If not , you will bulge in the middle , i.e. the tissues.

There are modifications to this : a minor part comes out via the lungs and feces , and these losses will grow at altitude, but not multiply.

There is a valid observation here , though : some headaches are caused by dehydration , and they will go away when you push fluids. Dehydration is also linked to AMS : loss of appetite is a precursor of nausea. Treating dehydration is good , preventing it is better (keep track of how much you drink , and the color of your urine) but pushing fluids after you´ve cured your headache will not give any better results in preventing AMS.

The fundamental flaw in the water myth though is that you are  working against the bodys way of adjusting to altitude :  the elevated red blood cell count that takes place the first days are achieved only through concentration – i.e. diminishing blood volume by higher urine output (see myth #2). This is a shift in fluid balance , technically mild dehydration – if you get  headache , the mechanism is out of whack and you should treat it.

There is a simple test for dehydration : check pulse after lying down for five minutes , and then again after standing up. Dehydration will givea marked  increased in pulse rate. Or just push a litre of fluid. Headache gone : fine , dehydration ,  now cured. Persisting headache : AMS , stop or descend.

The really fascinating thing about the water myth is the notion of ” the white coats may scoff at us , but we´ve come up with a really great idea.. ” Leaving the medical profession aside , the method  has been tried and tested , over oand over again : pilgrims , Silk Route merchants , Gurkha soldiers and many more have struggled to cope with the same problem for more than a thousand years , walking along rivers and sacred lakes  and tried everything at hand . If it worked , it would have caught on.

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Acclimatisation myths # 2 : The eBay bloodcell

May 9, 2007

This might seem like a petty point to make , but it is intimately linked to myth # 3 , so we´ll do it anyway.
Rapid ascents start physiological responses , and , after the higher respiratory and heart rate, the increased red blood cell production is the most commonly mentioned.

It seems straight forward : the body senses the lowered oxygen saturation as you ascend (more on that later) , orders some more hemoglobin , which is delivered.

One of the stumbling points here is delivery time : the unspoken assumption here is this a more or less Fed Ex-like process : sign the order and start looking for the mail man . This would be more like Indian mail , though : a blood cell is a complex product , and will take more than a week to produce.

As with other myths , there is a valid observation at work , with the wrong explanation .
Red blood cell concentration does go up , but it´s the same  old blood cells still going around : concentration goes up since the blood volume decreases after increased urine production. After descent the blood quickly goes back to normal values : don´t count on having a higher hemoglobin level a week after descending below 2000 meters.

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Acclimatisation myths # 1 : Been there , done that

May 8, 2007

Myths are are explanations of our world, based on experience. Today´s myths play out on the net , and woe unto the ones that question not the experience , but the explanation.

So , before trusting the experience , some quick reality checks when you hear someone cheering people merrily on to a quick jaunt up to a high camp , close to heaven :

1. Been where ?
You will be surprised at how many actually can´t describe where they´ve been – vertically. Discussing itineraries , especially the first inroads, is all about ascent rates : if the advice comes without a clear description of sleeping altitudes firstly , and max altitudes secondly it´s just not workable info.
Been where ? also includes another question : coming from .. ? – again , vertically . If that information is missing , get a good map , or go to Google Earth. Place limited trust in web searches : there is a lot just plain wrong intel out there : like the persistent myths of the worlds highest road , for instance.

2. Done it , really ?
Suggested itineraries often represent ..plans and dreams , not experience. The thing you´d want to do next time. Listen carefully , and you´ll hear that telling , far away voice talking about unfulfilled goals . Which is a form of poetry , well worth listening to. Make it another reason to go – but don´t exchange the map , with the elevation curves, for the poetry when you actually set out.

3. Done what ?
Going thru , and staying at , are two radically different things. There are vast numbers of travellers convinced that they -and you- can handle the altitude of x meters after having traversed a high pass. What can be learned from this is if you were able to handle that ascent profile : a long high plateau below a pass can , often will, hit harder than the high point of the journey.
Ever more important , sleeping poses a bigger challenge than staying awake , and upright.

4.Did it when ?
People will often react differently to rapid ascents , which feeds a perception that it´s a random process . If you look to the time before setting out , a lot of this randomness evaporates, and becomes consistent with the time spent acclimatising before setting out. The one time it started to go horribly wrong the difference between me and the unconscious fellow traveller next to me was the time spent at moderately high altitude before, a pattern that repeated itself in the rest of the group.

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