The Khumbu cough
You walk into the dining room at Lobuche (4,930m/16,200ft). There you see several trekkers coughing and immediately notice this cough is different. It is loud, rough and hoarse. As you retire to bed, you can hear this cough continuing in the neighboring rooms. Although it is very common and quite debilitating, very few trekkers prepare for the Khumbu cough as much as they worry about altitude sickness issues.
The Khumbu cough is a persistent hacking cough experienced at high altitude. Quite a few trekkers and mountaineers trekking in the Khumbu region (the region above Namche on the Everest Base Camp Trek or the Everest Three Passes Trek route) develop this kind of cough and hence the name “Khumbu cough”. In a survey of 283 trekkers walking in the Everest region of Nepal, 42% suffered from cough. In another study, again in the Everest region of Nepal, the prevalence of cough was found to be 22% between 4243 and 4937 m.
However, the Khumbu cough is not typical just to the Khumbu region. It can happen on any high-altitude trek such as the Manaslu Circuit Trek or the Kanchenjunga Base Camp Trek. It is more prevalent in the Khumbu region simply because of the sheer number of trekkers in the Khumbu area. Prolonged coughing can result in rib fractures and hemorrhoids rectal prolapse.
CAUSES:
Traditionally, it was believed that Khumbu cough is caused by breathing cold, dry air at HIGH ALTITUDE. This belief has been refuted by observations in long duration hypobaric chamber studies. Explorers on polar expeditions too are exposed to cold, dry air (though at lower altitudes) but do not seem to develop similar kind of cough. Instead, it is likely that altitude-related cough is a symptom of a number of possible perturbations in the cough reflex arc that may exist independently or together. These include:
- Loss of water from the respiratory tract
- Respiratory tract infections
- Sub-clinical high altitude pulmonary oedema.
While the exact reason for the Khumbu cough is not fully understood, read National Institute of Health’s detailed explanation of a number of potential mechanisms for the cause of high-altitude cough.
Other non-proven causes for the Khumbu cough include:
- Many at altitude are breathless and breathe through the mouth, thus bypassing the natural humidifying mechanism of the nose, cold air may be triggering the cough by “roughing up” the bronchial mucosa.
- Asthma like mechanisms are at work at high altitude which cause narrowing of the airways and cough.
- Low oxygen at high altitude.
- The inspiration of dust particles mixed with yak and donkey dung causing an infection in the respiratory tract.
STUDIES ON HIGH-ALTITUDE COUGH:
The first formal study of cough at high altitude took place during the 1994 British Mount Everest Expedition when 10 subjects trekking from 2800 m to Everest Base Camp at 5300 m underwent nocturnal cough frequency monitoring. Nocturnal cough frequency increased with increasing altitude.
Operation Everest II
In this study, eight subjects underwent a simulated ascent of Mount Everest in a hypobaric chamber. At altitudes above 7000 m the majority of the subjects developed pain and dryness in the throat and an irritating cough, despite the chamber being maintained at a relative humidity of between 72 and 82% and a temperature of 23°C. This brought into question the widely held view that cough at high altitude was due to the inspiration of dry, cold air.
Operation Everest III
In this hypobaric chamber study, eight subjects again underwent a simulated ascent of Mount Everest. During the experiment the temperature and relative humidity of the chamber were maintained at between 18 and 24°C and 30-60% respectively. Nocturnal cough frequency increased with increasing altitude and when the subjects descended to 5000 m to recuperate before the ascent to the “summit,” the cough frequency fell before increasing again on ascent to 8000 m. Cough frequency immediately returned to control values on descent to sea level.
The current understanding of altitude-related cough remains limited. From published work the only conclusions that can be drawn are that altitude-related cough exists and its prevalence increases with increasing altitude.
PREVENTION:
Below are some tips for preventing the Khumbu cough:
- Keep the bronchi moist by drinking hot or warm water
- Ascend slowly to allow for proper acclimatization.
- Wear a neck gaiter and cover your nose while on the trail. Avoid inhaling dust on the trail.
- Avoid over-exerting yourself as this will increase breathing rate and hence expose your lungs to more dry air
TREATMENT:
Possible treatments include:
- Suck on throat lozenges
- Wear a neck warmer or a balaclava during the day and during the night, if you can. This keeps the throat area warm and prevents cold air and particulates from irritating your lungs
- If the cough is really bad, then inhaling oxygen can help. In severe cases, one should consider descending and getting to lower altitudes as quickly as possible
- Cough suppressants or antihistamines
- Antibiotics to fight the infection
