Oxygen 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.