INTERVIEW WITH DR PETER YAN ON ALTITUDE SICKNESS
- From your experience, do you think that Singaporeans tend to think that altitude sickness is not a serious matter? Why?
Singaporeans are aware of altitude sickness especially people with heart conditions. Often, my patients and their families ask about safety of flying as well as going to resort mountains in China, Tibet, etc for holidays. So I think that they do consider this as a serious matter. However the young and healthy Singaporeans may not, an example would be like my daughter, aged 18 years old who went on a trip with her school to Nepal intending to reach the base camp of Mt Everest. Although an acclimatization program was done, still, there were several students who developed AMS. They obviously do not feel that this was a serious matter as their guides were able to treat them and those who developed AMS did not ascent further. Perhaps many may not know that when AMS is left untreated and further physical activities are embarked upon, that they may develop the more serious HAPE and HACE. The incidence of this happening is approximately between 2 to 4%. Approximately 20 deaths a year occur worldwide as a result of AMS progressing to HAPE and HACE.
However not all are aware that preparations are required to ascent or trek mountains to altitudes at or above 2500 meters (8500 feet) i.e. acclimatization. Several of the popular resorts in Malaysia like Genting Highland, Cameron Highlands, are not very high and are therefore safe.
Most commercial aircrafts in service today are pressurized but cabin pressures during flight is not maintained at sea level; cabin altitude of 1600 to 2700 meters (approximately 5000 to 8000 feet) are commonly encountered especially in newer jet aircrafts operating at higher flight levels. At these altitudes, arterial saturation in normal individuals would be 90% or more. Normal people should maintain arterial saturation above 90%. However patients with underlying lung disease, congenital right to left heart intracardiac shunts or heart failure may have significantly lower arterial saturations during the flights and therefore may be compromised (below oxygen saturation of 90% will lead to complications). Patients with recent heart attack without adequate treatment and revascularization, poorly-controlled high blood pressure and already existing low saturation oxygen in the blood for other causes like lung diseases, may have an increased risk of reduced blood supply to the heart and may therefore result in complications like heart attack or acute heart failure.
However having said that, spending a few hours at altitudes above 2500 meters (8500 feet) is usually not harmful to healthy people or even cardiovascular patients who have been stabilized and treated adequately. But longer stays and faster ascents to higher altitudes may aggravate underlying medical conditions associated with baseline blood oxygen saturation which is lower than the normal. With longer stays both patients and normal individuals are susceptible to developing acute mountain sickness and of course the rare progression to high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE) may be life-threatening if not treated properly.
- How many people do you see for this condition each year?
The frank answer is hardly any as acute mountain sickness occurs at the time of ascent to the mountain and the condition when diagnosed and treated promptly will result in recovery and therefore by the time they descend to sea level, there are no further symptoms of note. Furthermore in Singapore we do not have mountains of such high altitudes. We only have Bukit Timah Hills and therefore Singaporeans do not get AMS.
- I understand that altitude sickness can affect anyone. But why would those with underlying heart or lung problems be more at risk of developing the more dangerous HAPE and HACE?
The underlying main issue in high altitude as mentioned before is due to the lack of oxygen in the air, a condition known as hypoxia. It is well known that hypoxia will lead to an elevated brain volume and this brain volume is due to an increase at least in part by swelling of the brain as a result of water retention, a term called brain edema. Brain edema may occur as a result of brain cells damage or death due to lack of oxygen and also may be related to the vascular supply to the brain which again is related to a lack of oxygen at a high altitude. The brain edema if not controlled will lead to the compression of the brain, raised/elevated intracranial pressure and lead to change in the mental status and further deterioration into coma and brain death.
With regards to high altitude pulmonary edema (HAPE), the underlying mechanism is due to exaggerated hypoxic pulmonary hypertension i.e. the arterial pressure of the lungs are increased dramatically as a result of the lack of oxygen and triggers off lung cells (alveolar) fluid flooding. And so, the water in the lung will lead to acute lung injury and this forms a vicious cycle which accelerates further exudation of fluid from the lungs resulting in acute breathlessness and coughing out the fluid in the form of sputum which may be blood-stained.
Some of the altitude-induced cardiovascular changes include an increase heart rate, increase cardiac output, increase blood pressure, increase pulmonary artery pressure and increase sympathetic nervous stimulation. These changes will require the heart to work harder and therefore require more oxygenation to the muscles of the heart. The reduced oxygenation in the blood may lead to a decrease in blood supply to the muscles of the heart especially in people who have coronary artery disease and this may then lead to a heart attack and/or heart failure with resultant accumulation of fluids in the lungs (HAPE). People with lung problems who already have elevated pulmonary arterial pressure will risk further increase in pulmonary artery pressure as a result of ascending to high altitudes and will therefore precipitating pulmonary congestion (fluid in the alveolar – lung cells).
As far as the heart is concerned, a high altitude exposure is contraindicated in patients with unstable coronary artery disease who already experienced chest pain at a low to moderate workload at sea levels. Those who have a heart attack, balloon angioplasty and stents or bypass surgery should avoid travelling to high altitude for at least 3 months. Those who have been treated adequately for their heart problem can still be allowed to ascent but will have to limit the daily rate of ascent to about 300 to 400 meters to allow for proper acclimatization. If chest pain occurs during the ascent, no further ascent should be undertaken. Their physical activities should be limited and consideration to descend to lower altitudes is advised. Anti-anginal drugs can be administered to relief chest pains. In heart patients who are taking blood-thinning medications, i.e. anti-platelet therapy and also concomitant oral anti-coagulation, these patients should be strongly discouraged to seek high altitudes for prolonged periods especially in remote areas of the globe because of the risk of bleeding in the lungs, eyes and elsewhere.
- Why are women and obese people also more at risk of altitude sickness?
It is uncertain why women may have a slightly increased risk of altitude sickness. This may be related to their fitness. However in obese people, the reasons may include – lack of physical fitness, associated obesity with cardiac conditions like coronary artery disease, diabetes mellitus and metabolic syndrome, hypertension, lung disease and sleep apnoea.
- Would you recommend everyone who is going on mountain tours, treks – to see a doctor before embarking on their trip?
People who are young, fit and healthy who decide to take mountain tours or ascent to altitudes (below 2500 meters), there is no necessity to see a doctor. However acclimatization is still required and they need to seek experts in mountaineering for guidance and for planning their program before scaling such altitudes. People who have heart or lung conditions especially the elderly should obviously seek medical advice before embarking on such trips as indicated above.
- Is the combination of medications you listed in the word doc only available with doc’s prescription?
The 2 most common drugs used to prevent mountain sickness are Acetazolamide and Dexamethasone. Acetazolamide as mentioned increases renal excretion of bicarbonate and therefore improves the tissue oxygenation. This drug requires a prescription and there are side effects which include nausea and anorexia which need to be explained to the patient. However it is generally well-tolerated. It helps to improve or eliminate signs and symptoms of AMS. It improves initial acclimatization (when started at least one day before ascent) and can be stopped 4 to 5 days after arrival at altitude if the subject is asymptomatic. It should be noted that Acetazolamide will not prevent AMS when extremely fast ascent profiles are used.
Dexamethasone is a steroid which is very useful in reducing inflammation and brain edema and also elevate some of the unpleasant symptoms of acute mountain sickness. It acts through changes in the capillary permeability (to reduce fluid exudation) and prevent inflammatory chemical release. It is generally reserved for travelers who are unable to tolerate Acetazolamide or for patients with severe AMS especially HACE awaiting transfer to lower altitudes.
These 2 drugs usually should be in the medical emergency box when scaling high altitudes. Other emergency drugs include Frusimide which is a diuretic, i.e. a medicine which increases urine output to prevent or reduce edema in the brain and the lungs. Another medication is spirinolactone which is also known as a potassium-sparing diuretic which is very useful when added in combination with Frusimide.
Nifedipine is another drug that can be used to lower pulmonary artery pressure effectively. Phentolamine also significantly lowers the pulmonary artery pressure especially when administered with oxygen and therefore is useful as a temporarising measure before descend.
- Is it necessary to bring along these medications?
Definitely. However the indications of use, the doses required and the timing and duration of use need to be advised by the doctor or an expert mountaineer as they are not without side-effects.