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CLINICAL REVIEW: Andrew J Peacock ABC of oxygen: Oxygen at high altitude BMJ 1998; 317: 1063-1066 [Full text]

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Cardiovascular disease risks at high altitude

James A Litch   (7 January 1999)

Untitled

G Mitchell   (17 February 1999)

Ibuprofen and AMS

Steve Warner   (21 June 2000)

Cardiovascular disease risks at high altitude 7 January 1999
James A Litch Send response to journal: Re: Cardiovascular disease risks at high altitude	EDITOR--The risks of travelling to high altitude regions vary significantly by the degree of remoteness and mean elevation (moderate high altitude 2500 – 3500 m, very high altitude 3500 – 5500 m, and extreme altitude >5500 m). The recommendations Peacock offers pertaining to the cardiac disease risks at altitude do not take these important factors into consideration.(1) Peacock states that the evidence as far as heart disease is concerned is encouraging, but in doing so ignores the limitations of the existing studies. There is limited data from moderate altitude in Europe and North America, but caution should be used when extrapolating these data to very high and extreme altitudes where the physiology differs. There are several anecdotal accounts and two published case reports that call attention to episodes of acute myocardial infarction and sudden death at very high and extreme altitude.(2,3) One should not interpret the limited number of reports as evidence that travel to altitude with heart disease is without significant risk. High altitude exposure commonly involves remote and less developed regions of the world. This is especially true for very high and extreme altitude regions. For the few physicians practicing in these remote areas, it is extremely difficult to document a case series of cardiac events or quantify risks. Confirmatory tests are not typically available. Evacuations are often urgently conducted. Follow-up and outcome data are unfortunately lost to frequent facility transfers, language barriers, unavailability of autopsy, and repatriation. The lack of reports may reflect these circumstances, rather than an absence of clinical cases or morbidity. Our experience at very high and extreme altitudes over several years at Kunde Hospital (3860 m) in the Mt. Everest Region of Nepal, the Himalayan Rescue Association Aid Posts in Manang (3535 m) and Pheriche (4243 m), Nepal, and on several climbing expeditions (up to 8848 m) suggests concern for travellers with heart disease to remote high altitude areas. We suspect that there may be an increased risk of sudden death and significant deterioration in cardiac symptoms at very high and extreme altitude. For example, during the 6 week peak visitation period this autumn in the Khumbu region of Nepal, nearly 8,000 visitors entered the high altitude national park. Within this group there was one sudden death from suspected myocardial infarction, one sudden death from suspected pulmonary embolism, three evacuations for acute chest pain syndrome, one suspected subarachnoid bleed requiring manual ventilation, and numerous patients treated for moderate and severe altitude sickness. As the number of older and less healthy trekkers with chronic disease continues to increase, one might reasonably expect additional cases. Advice to patients with cardiovascular disease considering travel to high altitude, even if stable, should include a discussion to determine the remoteness and altitude of the area to be visited. Any additional risks due to absence of medical facilities should be communicated. Patients should also be informed that although moderate high altitude may not increase risks, any added risks that exposure to very high or extreme altitude might contribute is at best unknown as there is a conspicuous void of data in the medical literature. James A. Litch Codirector and Physician Rachel A. Bishop Codirector and Physician Kunde Hospital Solukhumbu District PO Box 224 Kathmandu, Nepal No conflict of interests 1 Peacock AJ. ABC of oxygen. Oxygen at high altitude. BMJ 1998;317:1063-6. (17 October.) 2 Hutchison S, Litch JA. Acute myocardial infarction at high altitude. JAMA 1997;278:1661-2. 3 Litch JA, Basnyat B, Zimmerman M. Subarachnoid hemorrhage at high altitude. West J Med 1997;167:180-1.
Untitled 17 February 1999
G Mitchell Send response to journal: Re: this article	Dear Sir I have just come across Andrew J Peacock's summary of the effects of high altitude ("Oxygen at high altitude": BMJ 317: 1063-1066, 1998). One comment made is that "at altitude hypoxia does increase ventilation, but usually only when the inspired oxygen pressure is reduced to about 13.3 kPa (3000m altitude)." As a physiologist living in Johannesburg (ca 1700m altitude) I should like to suggest that this comment perpetuates a misconception. The average person living in Johannesburg, where atmospheric PO2 is 17 kPa, has a PaO2 of 11 kPa (85mmHg) and a PaCO2 of 4.5 kPa(35mmHg). If CO2 is the main stimulus to ventilation how can PaCO2 be 35mmHg in Johannesburg but 40mmHg at sea-level? Our conclusion is that hypoxic drive begins at altitudes far lower and at atmospheric PO2 far higher than those suggested by laboratory experiments. The PaCO2 in Johannesburg is a reflection of this effect: PaCO2 is inversely related to alveolar ventilation. Further support for our conclusion, if it is correct, is that an adjustment to plasma pH regulation should be a consequence. This is indeed the case: the average Johannesburger has a plasma HCO3- concentration of 21 mmol/ which is significantly lower than its concentration at sea-level, but a concentration completely appropriate if plasma pH is to be 7.4, which it is. Thus our physiological data suggest that at quite low altitudes hypoxia causes an increase in alveolar ventilation (at least in people who live at these relatively low altitudes) and a consequential reduction in PaCO2. To compensate for the lower PaCO2, plasma HCO3-concentrations are adjusted downwards by the usual mechanisms. As an aside in one of Dr Peacock's diagrams (p 1064) there is a suggestion that at 1500m altitude impaired night vision occurs. I am not aware that this is a problem here. Yours faithfully G Mitchell PROFESSOR HEAD: DEPARTMENT OF PHYSIOLOGY Wits Medical School
Ibuprofen and AMS 21 June 2000
Steve Warner Send response to journal: Re: Ibuprofen and AMS	The article reccommends Paracetomal as a treatment for the onset of AMS symptoms. Does Ibuprofen work as well/better? Any suggestions please.