High Altitude MedicineScott R Valent MD

High Altitude Medicine● University of Vermont College of Medicine● Multiple high altitude treks in Nepal,

Pakistan, Tibet● Travels in Peru, Ecuador, Argentina, Bolivia● Aconcagua● Cardiologist

Highest cities in the world

● Lhasa, Tibet 12,000 ft● La Paz, Bolivia 11,910 ft● Cuzco, Peru 11,152 ft● Sucre, Bolivia 9,331 ft● Quito, Ecuador 9,249 ft.● Toluca, Mexico 8,793 ft.● Bogota, Columbia 8,675 ft.● Addis Ababa, Ethiopia 7,900 ft.● Asmara, Ethiopia 7,789 ft.

Altitude Facts

● The percentage of oxygen at altitude is the same as sea level, approximately 21%

● Atmospheric and partial pressure decrease with altitude, allowing less oxygen availability

● Barometric pressure 760mmHg sea level● Barometric pressure 253mmHg Mt Everest● Pressure 222mmHg at 67 degrees N lat.

Altitude sickness

Anyone traveling to high altitude may be at risk for developing altitude sickness

● AMS● HAPE● HACE

Physiology at altitude●

Physiologic effects of altitude

High altitude 5,000-11,500 ft. (1,500-3,500m)● AMS common with rapid ascent● Decreased exercise capacity● Pulse oximetry pOx>90%

Physiologic effects of altitudeVery High Altitude 11,500-18,045 ft (3500-5500m)● Most common range for severe high

altitude illness● Abrupt ascent dangerous● Pulse Oximetry 75-85%● Extreme hypoxia may occur during

sleep, exercise and high-altitude illness

Physiologic effects of altitudeExtreme altitude 18,000-29,035 (5500-8850m)● Progressive deterioration outstrips

acclimatization● Humans cannot permanently live at these

altitudes● High likelihood of severe high-altitude illness

with rapid ascent● Pulse oximetry 58-75%

Acclimatization

● Immediate: Rapid breathing and HR● Increased catecholamines● Dehydration● Pulmonary artery pressure increases● Increase in hematocrit within 4 days● Increase in 2,3-DPG

Cheyne-Stokes Breathing

● “Hey, my tentmate stopped breathing”

● The respiratory drive, particularly while sleeping is primarily driven by CO2

● At altitude CO2 levels are typically lower and breathing may be initiated by decreased O2.

● This leads to erractic breating, with long, frightening pauses.

Risk categories for acute mountain sicknessRisk category Description Prophylaxis

recommendation

LOW People with no prior history of altitude illness and ascending to <9,000ft.People taking >2 days to arrive at 8,000-9,000feet with subsequent increases in sleeping elevation <1,600 feet/dy, and an extra day for acclimatization every 3,200 feet

Acetazolamide prophylaxis is generally not indicated

MODERATE People with prior history of AMS and ascending 8,000-9,000 feet in one dayNo history of AMS and ascending to >9,000 feet in 1 dayAll people ascending >1,600 ft per day at altitudes above 9,000 ft., but with an extra day for acclimatization every 3,200 feet

Acetazolamide prophylaxis would be beneficial and should be considered

HIGH

Hackett, P.H. Altitude illness, 2014 yellow book

History of AMS and ascending to >9,000 feet in 1 dayAll people with a prior history of HACE or HAPEAll people ascending to >11,400 feet in one dayAll people ascending to >1,600 feet per day above 9,000 feet, without extra days for acclimatizationVery rapid ascents (such as <7 day ascents of Mount Kilimanjaro

Acetazolamide prophylaxis strongly recommended

Acute Mountain Sickness(AMS)

● Very common○ 15-30% of colorado resort skiers○ 50% of Mt. McKinley climbers○ 70% of Mt. Ranier climbers

Lake Louise CriteriaAcute Mountain sickness

● Headache plus at least one of the following:

○ fatigue or weakness○ nausea,vomiting, anorexia○ dizziness, lightheadedness, insomnia

HAPEDefinition: Accumulation of fluid in the lungs leading to hypoxiaUnrelated to AMS

● Incidence: 0.1-5%● Often manifests at night, frequently

the second night● Can progress rapidly● May lead to HACE

Lake Louise CriteriaHAPE

● At least two of the following symptoms:

○ Dyspnea at rest○ Cough○ weakness or decreased exercise

performance○ Chest tightness or congestion

Lake Louise CriteriaHAPE

● At least two of the following signs:

○ Central cyanosis○ rales or wheezing○ Tachypnea○ Tachycardia

HAPERisk Factors● Young, fit males● Exertion● Cold

HAPE-Treatment● Treatment of choice is descent

(2,000 feet)● Oxygen● Nifedipine, Sildenafil● Gamow Bag● Mortality rate for untreated HAPE

may be up to 44%

HACE

● Treatment● Immediate descent● Oxygen● Steroids-Decadron● Gamow bag

Treatment

Gamow bag

Gamow bag

Golden rules of high altitude medicine

● If you are sick at high altitude, it is altitude sickness until proven otherwise

● Never ascend with symptoms of AMS● If you are deteriorating or have signs

or symptoms of HAPE or HACE, descend immediately

Medications/DosagesAcetazolamide/Diamox

Indication

AMS, HACE prevention

AMS treatment

Hackett, P.H. Altitude illness, 2014 yellow book

Route

oral

Oral

Dose

125mg twice a day250mg twice a day if over 100KG

250mg twice a day

Medications/DosagesDexamethasone

Indication

AMS, HACE prevention

AMS, HACE treatment

Hackett, P.H. Altitude illness, 2014 yellow book

Route

oral

oral, iv, im

Dose

2mg every 6 hours, or 4mg every 12 hrs

AMS: 4mg every 6 hrs.HACE: 8mg once, then 4mg every 6 hrs.

Medications/DosagesNifedepine

Indication

HAPE prevention

HAPE treatment

Hackett, P.H. Altitude illness, 2014 yellow book

Route

oral

oral

Dose

30mg SR (slow release) every 12 hrs or 20mg SR every 8hrs

30mg SR every 12 hrs. or 20mgSR every 8 hrs.

Medications/DosagesSildenafil (Viagra)

Indication

HAPE prevention

Hackett, P.H. Altitude illness, 2014 yellow book

Route

oral

Dose

50mg every 8 hrs.

Prevention● One night at an altitude slightly below 10,000 feet● At altitudes above 10,000 feet, increase sleeping

altitude by only 1,000-1,500 feet per night● Spend a second night at the same altitude for every

increase of 3,000 ft.● Example : Aconcagua:with a generous 1,500 foot

per night increase, plus several rest and weather days, expect 9-10 days prior to summit night at 20,000+ feet

PreventionAcetazolamide● Diuretic used to help hasten acclimatization● 250-1,000 mg daily● Mechanism: During initial time at altitude

rapid breathing decreases CO2 and decreases acidity of blood

● Acetazolamide helps acidify blood● Improves symptom scores for AMS● may improve sleep● Does not protect against AMS with ascent

Other hazards at altitude

Bronchitis/chronic cough

● Cool extremely dry air-hyperventilation, mouth breathing

● Cough● Broken ribs● Can mimic HAPE

Sunburn

● UV intensity increases 4% per 1,000 feet● at 18,000 feet 72% more sun exposure, not

including snow reflection

Ultraviolet Keratitis● Snow blindness● Corneal damage from UV light● Damage can occur in one hour● Symptoms may not develop for

6-12 hours● PREVENTION

Frostbite

Summary● Prevention is critical● Golden rules● Early diagnosis and descent● As one travels higher the

margin for error decreases significantly

Questions?

Recommended websites

● Altitude.org● BasecampMD.com● http://www.high-altitude-medicine.com/● CDC chapter by Peter Hackett: http://wwwnc.

cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/altitude-illnesshttp://wwwnc.

cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/altitude-illness