Altitude illness
BMJ 2003; 326 doi: https://doi.org/10.1136/bmj.326.7395.915 (Published 26 April 2003) Cite this as: BMJ 2003;326:915All rapid responses
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We are grateful to Professor Guillebaud for drawing attention to the
difficulty in advising women taking the combined oral contraceptive pill
(COC) who wish to ascend to altitude in his letter posted in response to
our article (1). Whilst we agree with his view that there may be an
increased risk of thrombosis for women travellers at high altitude who
choose to take the COC, as a result of summation of risk factors, we feel
that the paucity of data makes it impossible to be prescriptive about the
altitudes at which use of this drug might or might not be safe. By
convention high altitude starts at 2500m and it would seem reasonable that
this is used as the cutoff for advising women about this issue. However,
we cannot see justification for defining specific altitudes above 2500m in
relation to summative risk of thrombosis for those taking the COC as there
is no data on which to base these assumptions. An additional problem in
defining altitudes of risk without taking other factors into consideration
arises because it is possible that long periods of travel at moderate high
altitude carry a similar risk of thrombosis as do shorter exposures at
very high altitudes. In the absence of evidence to guide practice, we
would therefore recommend that the possibility of an increased risk of
thrombosis is discussed with all COC-taking travellers ascending above
2500m and that the merits of alternative methods of contraception are
considered in each case.
Andrew J Pollard and and Peter W Barry
1 Barry PW, Pollard AJ. Altitude illness. BMJ 2003;326:915-19
Competing interests:
None declared
Competing interests: No competing interests
We read with interest the review on altitude illness by Pollard and
Barry1 but noted that there was no mention of the ophthalmological effects
of ascending above 2500m. A good detailed review is available for
specialists2 but there are several areas of interest to the general
physician.
Firstly the effects at altitude of LASIK surgery which is becoming
increasingly popular amongst the general public. A recent study of 6
climbers on Mount Everest, 4 of whom reached the summit, showed that 3
climbers suffered transient blurring of vision which improved with
descent.3 Another report of 2 climbers on Aconcagua also showed a
transient myopic shift, although they were in the early post-operative
period.4 So it appears that those who have had LASIK surgery should be
prepared for some blurring of vision at altitude which will recover on
descent.
Secondly, snow blindness is a complication of failing to use
protective sunglasses with sidepieces. Snow blindness is sunburn of the
cornea and presents with intense pain, photophobia and itchy red eyes. It
is especially common at high altitude because there is less atmosphere and
pollution to absorb harmful UV radiation and often there is snow on the
ground which reflects the sun’s rays. At high altitude snow blindness is
potentially more serious due to a slower epithelial healing time secondary
to hypobaric hypoxia, and poor hygiene which make infection more likely;
in a remote environment, this can be sight threatening.
Finally, high altitude retinopathy (HAR) is a pathological response
by the retina to the hypoxia of altitude. It occurs in up to half of those
ascending above 2500m and can be dramatic in appearance. Flame
haemorrhages are most commonly seen but cotton wool spots, dot and blot,
and pre-retinal haemorrhages have also been reported. Although HAR can
occur in association with altitude sickness, it is usually asymptomatic
and haemorrhages resolve without sequelae. Haemorrhage involving the fovea
may produce a positive scotoma which may clear within a few days or last
up to a year. Retinal vascular dysregualtion may be a sign of poor
acclimatisation and a predictor of more serious high altitude cerebral and
pulmonary oedema.5
Daniel S Morris MRCOpth.
Tennent Institute of Ophthalmology,
Gartnavel General Hospital,
Great Western Road,
Glasgow
danielsmorris@hotmail.com
Paul Richards, MRCGP. DFFP. MSc.
The Surgery,
64 London Road,
Wickford, Essex.
paul@medex.org.uk
References
1. Barry PW and Pollard AJ
Altitude illness
BMJ 2003; 326: 915-919.
2. Karakucuk S and Mirza GE
Ophthalmological effects of high altitude
Ophthalmic Res 2000; 32: 30-40
3. Dimmig JW, Tabin G.
The ascent of Mount Everest following laser in situ keratomileusis.
J Refract Surg. 2003 Jan-Feb;19(1):48-51.
4. Boes DA, Omura AK, Hennessy MJ.
Effect of high-altitude exposure on myopic laser in situ keratomileusis.
J Cataract Refract Surg. 2001 Dec;27(12):1937-41.
5. Wiedman M and Tabin GC.
High altitude retinopathy and altitude illness
Ophthalmology 1999; 106: 1924-1927
Competing interests:
DM and PR are members of Medex, a limited company which supports the activity of Medical Expeditons, a charity that promotes research and education into high altitude physiology and medicine.
Competing interests: No competing interests
EDITOR - I found the Clinical review by Drs Barry and Pollard in the
BMJ of April 26th fascinating and practically informative [1] . The
advice regarding pregnant women was interesting, partly for the continuing
paucity of data. But I wonder what their current advice would be to young
female climbers and trekkers who are not pregnant, indeed wish to avoid
pregnancy (probably a larger group), with respect to the combined oral
contraceptive (COC)?
Fluid loss by diuresis or inadequate intake; trauma; immobility in
tents when the weather closes in; all these in altitude illness can
potentially increase the established risk of venous or arterial
thrombosis, and moreover the leading contender to explain high altitude
pulmonary oedema is patchy pulmonary hypertension. It is well recognised
that high risk of either condition contraindicates the COC - the critical
question is at what level of altitude the risk becomes high enough to make
the contraindication "absolute" (ie WHO 4, on the 1-4 scale now
recommended [2])?
Autonomy is an important principle here: rock-climbing is orders of
magnitude more dangerous than any risks modifiable by choice of
contraceptive! The woman must have freedom to take some added risk. But
the prescriber has autonomy too, if s/he considers the added risk of COC
unacceptable - especially given the arrival in the UK of new highly
effective alternatives to it (Implanon[tm], Cerazette[tm], banded copper
IUDs and the Mirena-IUS [tm]), which are completely free of the pro-
thrombotic substance, ethinylestradiol.
Would Barry and Pollard agree with my current recommendation, pending
further data, that women should avoid the COC (WHO 4 - 'Do not use') if
planning to ascend to above 4500 metres: this being about midway in the
range 3500-5800 metres where, according to their Box 1, altitude illness
is "common" even if there is no rapid ascent ?
In the lower range 2500 to 3500 metres, would they also agree that
the additional presence of a significant venous or arterial risk factor
(eg BMI above 30, heavy smoking) would raise the category to WHO 4? (Women
with two such risk factors should not use the COC even at sea level!)
Otherwise in the range 2500-4500 metres, in women with no known added
risk factors WHO 3 (Caution) would apply. This means alternative
contraceptives are preferable BUT, if these are unacceptable or
contraindicated, the woman may with no promises of safety make an informed
choice to continue taking the COC.
J. Guillebaud
Emeritus Professor of Family Planning and Reproductive
Health,
Dept of Obstetrics and Gynaecology, University College, London, WC1E 6HX
1 Barry PW, Pollard AJ. Altitude illness. BMJ 2003;326:915-19.
2 Guillebaud, J. (2001) . Medical eligibility criteria for
contraceptive use. Lancet, 357, 1378-79.
Competing interests:
JG has received lecture fees, research grants, expenses and ad hoc consultancy fees from the manufacturers of contraceptive products.
Competing interests: No competing interests
As a newly qualified doctor and a trekking enthusiast, I was lucky enough to participate as the camp doctor for three high altitude Himalayan trekking expeditions. From my personal experience, even experienced climbers can suffer from high altitude sickness if they don't take the acclimatisation seriously enough.
Often enough, young enthusiastic males with some experience in high altitude trekking don't take the acclimatisation seriously. The consequences in them can be extremely dangerous.
Competing interests:
None declared
Competing interests: No competing interests
Editor-Barry & Pollard suggest in their clinical review of
altitude illness that gingko biloba may be more effective than placebo in
preventing symptoms of acute mountain sickness(AMS). I wish to draw
attention to the PHAIT study carried out by Gertsch et al in Nepal,
October to November 2002 in which gingko biloba,acetazolamide &
placebo were directly compared in a randomised controlled trial of
trekkers ascending from Pheriche(4250m) to Lobuche(4850m). A total of 614
subjects were enrolled and the results showed a marginal increase in AMS
symptomsin the gingko biloba group (61.3%) compared w the palcebo
group(53.8%), with the lowest incidence of AMS symptoms being in the
acetazolamide group(21,.2%).
On the basis of this study I would suggest that gingko biloba can not
be recommended as prophylaxis of AMS symptoms.
P.Kenrick
1 Prevention of High Altitude Illness Trial. Gertsch J,Basnyat B,et
al.Personal communication of results from J.Gertsch
Competing interests:
I was a volunteer doctor at Himalayan Rescue Association Aid Post Pheriche during the period of the PHAIT study although not directly involved in the study.
Competing interests: No competing interests
Barry and Pollard (1) concede that medical treatments for acute
mountain sickness (AMS) and the potentially fatal high altitude pulmonary
oedema (HAPE) and cerebral oedema (HACE) are limited. Appropriately, they
restrict their discussion to those therapies that already rest on a sound
evidence base. We would like to draw attention to the potential use of a
class of drugs that were once proposed to be a panacea for a broad range
of pathologies, but which have so far yielded largely disappointing
results: antioxidants.
The best evidence for the efficacy of antioxidant therapies comes
from the Medex group, in a trial conducted by Bailey & Davies, which
showed a significant reduction in symptoms of AMS compared with placebo in
a group of 15 climbers taking a cocktail of antioxidant vitamins (2).
There is growing evidence for a role for oxidative stress, which is
mitigated by antioxidants, in the pathogenesis of altitude illness. A
direct consequence of hypoxia, oxidative stress may augment hypoxic
pulmonary vasoconstriction (3), alter pulmonary endothelial permeability,
impair red cell function (4) and lead to brain interstitial oedema. If it
could be achieved, effective supplementation of antioxidant systems at
tissue level is likely to be of benefit in mountain illness.
The importance of raised pulmonary artery pressures in the
development of HAPE in susceptible subjects is also discussed by Barry and
Pollard. A recent study demonstrated that oral sildenafil, by its action
on the eNOS-NO-cGMP pathway, successfully attenuates the increase in
pulmonary artery pressure in humans acutely exposed to hypoxia (5). It has
been postulated that Viagra may have a role in preventing pulmonary oedema
at altitude.
Barry and Pollard highlight the activities of Medex, a charity with a
distinguished history of work in this field of research. Further to the
activities mentioned in the article, Medex also helped a group of medical
students found the Edinburgh-based altitude research charity, Apex. By
contributing equipment and advice, they catalysed the success of this
group’s first expedition, Apex Bolivia 2001. Research in this field is
often very dependent on collaborative work, and we are very grateful to
Medex for their continuing support.
This summer, our group will test the use of antioxidant
supplementation and oral sildenafil in two double-blind placebo-controlled
randomised trials with 125 subjects at the Bolivian Institute of High
Altitude Biology (IBBA) laboratory at Chacaltaya (5200m) in Bolivia.
Reference List
1. Barry PW,.Pollard AJ. Altitude illness. BMJ 2003;326:915-9.
2. Bailey DM,.Davies B. Acute mountain sickness; prophylactic
benefits of antioxidant vitamin supplementation at high altitude. High
Alt.Med.Biol. 2001;2:21-9.
3. Weissmann N, Tadic A, Hanze J, Rose F, Winterhalder S, Nollen M et
al. Hypoxic vasoconstriction in intact lungs: a role for NADPH oxidase-
derived H(2)O(2)? [In Process Citation]. Am.J.Physiol Lung Cell
Mol.Physiol 2000;279:L683-L690.
4. Celedon G, Gonzalez G, Sotomayor CP, Behn C. Membrane lipid
diffusion and band 3 protein changes in human erythrocytes due to acute
hypobaric hypoxia. Am.J.Physiol 1998;275:C1429-C1431.
5. Zhao L, Mason NA, Morrell NW, Kojonazarov B, Sadykov A et al.
Sildenafil inhibits hypoxia-induced pulmonary hypertension. Circulation
2001;104:424-428.
Competing interests:
None declared
Competing interests: No competing interests
It is appropriate that this paper has appeared in the BMJ coninciding
with the 50th anniversary of Hillary and Tensing's pioneering climb which
occurred at the same time as the Queen's Coronation in 1953.
I have never been a real climber myself- the conquest of Snowdon
being my only achievement. However, when the BMA organised joint overseas
meetings in the 60's & 70's, we had the pleasure of hearing Hillary
give the inaugural lecture in Hong Kong in 1969 - his subject being an
illustrated lecture on his 1967 expedition in India entitled 'From the Sea
to the Sky'. He and his party (including his son) navigated the Ganges
from its delta to its source (at approximately 20,000 feet) in the lower
range of the Himalayas. This was by no means a straightforward exercise
for these experienced climbers - they were feted by local dignatories
along the whole route, only escaping their attentions when in mid-stream
in their outboard-powered inflatables.
On nearing their destination Hillary himself developed the full
picture of mountain sickness and had to be evacuated by air. The account
of this is well documented in the bood Hillary published (From the Sea to
the Sky) at about the time of his BMA Hong Kong lecture. His friend,
Colin Aikman, (a personal friend of mine) who was then New Zealand's High
Commissioner in Delhi, was responsible for organising the helicopter
resuce by the Indian Air Force. Hillary made a rapid recovery at the
nearest Air Force hospital, his son and his party going on to achieve the
projected summit. Edmund Hillary was by then in his 60's and had no
chance of acclimatisation on his lengthy journey starting at sea level
along the Ganges.
The BMJ article is a warning to those ameteur trekkers who are
tempted by so called walking holidays in Nepal and surrounding area, often
flying in to base camp by plane.
Yours sincerely
H Max White MRCGP
Fellow BMA
Competing interests:
None declared
Competing interests: No competing interests
With interest we read the recent review by Barra and Polard on
altitude sickness (1). Especially for travellers, early risk indicators
would be helpful to avoid especially the more severe forms of the
syndrome. It is well known, that Tibetans and Sherpas (of Tibetan origin)
have better physical performance at high altitude than caucasians (2),
possibly due to genetic differences (3). Acute adaptation to high altitude
and low oxygen supply primarily takes place by hyperventilation. By this
means not only oxygen saturation (sO2) improves, but blood pH raises as
well. It appears that the need to oxygenate tissues conflicts with the
need to maintain H+ homeostasis. The result is a compromise between the
respiratory adjustment aimed at increasing blood alkalosis in order to
optimize the O2 transport system. The capability to correct respiratory
alkalosis is thus crucial for acute adaptation to high altitude. Sherpas
have been shown to have a more efficient adaptation to hypoxia, that
allows to limit alkalosis through a lower ventilatory drive and to
maintain arterial sO2 at the same partial oxygen pressure (pO2) by
decreasing the 2,3-diphosphoglycerat/haemoglobin ratio (4).
During a hiking tour at high altitude (Mt. Kailash, Tibet) we measured pO2
in 9 Austrians (all caucasians, 4 males and 5 females, aged 43–62 years)
and 7 Sherpas (5 males and 2 females, aged 28-62 years). Preadaptation
periods and physical fitness in Sherpas and caucasians where about the
same before the test was performed. The examined Sherpas lived at
Katmandu, Nepal (1500m) and caucasians in Innsbruck, Austria (550m). Basal
sO2 was measured at rest and during one minute of forced hyperventilation,
at altitudes of 5100m above sea level (Darchen, Mt. Kailash) and at 5600m
(Dolma La, Mt. Kailash) using a small portable transdermal pulse oxymeter
(NONIN Medical Inc., Plymouth, MN, USA). Sherpas had significantly lower
resting sO2 but on hyperventilation they were able to rise their sO2 up to
>90% while caucasians had higher basal sO2 and a significantly lower
capacity to rise their sO2. In both groups the increase in sO2 over
baseline values (sO2 = hyperventilation capacity) was
significantly lower at 5600m compared to the HC at 5100. Subjects with a
hyperventilation capacity <5% at 5100m showed mild signs of acute
altitude sickness like headache, dyspnoea or subcutaneous edema when they
ascended to 5600m while all others who had a HC *5% at the base camp
(5100m) had no complaints.
From the data we conclude that hyperventilation capacity decreases with
increasing altitude and its measurement might be suitable approach to
predict the development of altitude sickness.
Maximilian Ledochowski M.D.
Dietmar Fuchs Ph.D.
Department of Internal Medicine, Institute of Medical Chemistry and
Biochemistry
University of Innsbruck, A-6020 Innsbruck, Austria
1. Barry PW, Pollard AJ. Altitude sickness. Brit Med J 2003;326:915-
9.
2. Chen QH, Ge RL, Wang XZ, Chen HX, Wu TY, Kobayashi T et al. Exercise
performance of Tibetan and Han adolescents at altitudes of 3,417 and 4,300
m. J .Appl Physiol 1997;83:661-7.
3. Beall CM, Blangero J, Williams-Blangero S, Goldstein MC. Major
gene for percent of oxygen saturation of arterial hemoglobin in Tibetan
highlanders. Am J Phys Anthropol 1994;95:271-6.
4. Samaja M, Mariani C, Prestini A, Cerretelli P. Acid-base balance
and O2 transport at high altitude. Acta Physiol Scand 1997;159:249-56.
Competing interests:
None declared
Competing interests: No competing interests
Bounous showed years ago that gut mucosal injury induced by ischaemia
may be prevented not only by intraluminal oxygen but also by intraluminal
glucose(1). An energy deficit induced by hypoxia at high altitude in a
healthy subject might, therefore, be normally overcome by a compensatory
increase in blood glucose or rate of glucose turnover.
In a diabetic a metabloc energy deficit might, therefore, be caused
by the hypoxia alone and/or by the accompanying impairment of the ability
to metabolise glucose efficiently(2). In which case hypoxia might be used
as a provocative test to help fine-tune diabetic management and prevent
late complications.
1. Bounous G. Role of the intestinal contents in the pathophysiology
of acute intestinal ischemia.
Am J Surg. 1967 Sep;114(3):368-75. Review.
2. SARS and the risk of mass extinction
Richard G Fiddian-Green (26 April 2003)Rapid response to: SARS virus
identified, but the disease is still spreading
Jane Parry BMJ 2003; 326: 897
2.
Competing interests:
None declared
Competing interests: No competing interests
Re: Altitude sickness in the experienced climber
My experience shows expert climbers have a lower risk for developing of
AMS.
In two separate studies we found that the experience of climbers has positive effect
on the prevention of AMS. In both studies, we divided trekkers into 3 groups
based on the number of ascents they had made to altitudes above 4000 m in
the last 6 months: experienced (more than 6 ascents), semiexperienced (1–5
ascents), and inexperienced (no
ascents). In teh first study, AMS developed in 41.3% of experienced climbers,
57.8% of semiexperienced, and 68.9% (131/190) inexperienced
(P.value=0.001)[1]. In a recent study, AMS developed in 18.7%, 51% and
61.9%, respectively (P.value=0.001). In recent study, by logistic
regression analysis and after omitting confounding factors previous trekking
skills on incidence of AMS[2].
V. Ziaee MD
Sports Medicine Research Center, Tehran University of Medical Sciences, IR
Iran
References:
1- Ziaee V, Yunesian M, Ahmadinejad Z, Halabchi F, Kordi R, Alizadeh R,
Afsharjo HR. Acute mountain sickness in Iranian trekkers around Mount
Damavand (5671m) in Iran. Wild Environ Med .2003; 14(4): 214-9.
2- Ziaee V, Alizadeh R, Mansournia MA, et al. The effect on ascending path
on incdence of AMS. (under review).
Competing interests:
None declared
Competing interests: No competing interests