High Altitude Medicine
Scott McIntosh, MD, MPH
Director, EMS/Wilderness Medicine Fellowship
University of Utah
Connecticut
Why study?
1. Live in or travel to high areas
Why study?
1. Live in or travel to high areas
2. Excellent physiology
Why study?
1. Live in or travel to high areas
2. Excellent physiology
3. Expedition medical director
14,000 ft Camp
The Plan
• Definitions
• Acclimatization - by system
• Specific problems:
– Acute Mountain Sickness (AMS)
– High Altitude Cerebral Edema (HACE)
– High Altitude Pulmonary Edema (HAPE)
How high is high?
29,000
Extreme
18,000
Very High
12,000
High
8,000
Medium
5,000
Low
0
Acclimatization
• Definition: series of
adaptations the body
undergoes when exposed to
high altitude for extended
periods
• Fascinating and complex
physiology
Altitude
PB
PIO2
PaO2 PaCO2
meters
mm Hg
mm Hg
mm Hg
Sea level
760
150
90
40
4200
440
83
48
27
6000
354
64
40
21
8000
280
49
34
12
8848
253
43
30
8
mm Hg
Lowlander
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
Base Camp
To top ice fall then Base Camp
Rest (Base Camp)
Rest (Base Camp)
Base Camp to Camp I
Touch Camp II then back to Camp I
Camp I to Base Camp
Rest (Base Camp)
Rest (Base Camp)
Base Camp to Camp I
Camp I to Camp II
Rest (Camp II)
Part way up Lhotse face then to
Camp II
Camp II to Base Camp
Rest (Base Camp)
Rest (Base Camp)
Rest (Base Camp)
Base Camp to Camp II
Rest (Camp II)
Camp II to Camp III
Yellow Band then to Camp II
Base Camp
Wait for weather window
Lowlander
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
Base Camp
To top ice fall then Base Camp
Rest (Base Camp)
Rest (Base Camp)
Base Camp to Camp I
Touch Camp II then back to Camp I
Camp I to Base Camp
Rest (Base Camp)
Rest (Base Camp)
Base Camp to Camp I
Camp I to Camp II
Rest (Camp II)
Part way up Lhotse face then to
Camp II
Camp II to Base Camp
Rest (Base Camp)
Rest (Base Camp)
Rest (Base Camp)
Base Camp to Camp II
Rest (Camp II)
Camp II to Camp III
Yellow Band then to Camp II
Base Camp
Wait for weather window
Sherpa
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Base Camp
Base Camp
Base Camp
Base Camp
Base Camp
Base Camp to Camp II
Rest (Camp II)
Base Camp
Base Camp
Wait for weather window
Respiratory
•
Hypoxic Ventilatory Response
1. Carotid bodies sense decreased pO2
2. Central medullary receptors sense pH changes
(CO2 diffuses across, dropping pH)
•
Response is genetically predetermined
•
South American vs. Himalayan natives
Hypoxic Ventilatory Response
Altitude (ft)
Resp Rate
Min Vent (L/min)
0
12
8
12,000
14
10
18,000
15
11
24,000
27
23
Am J Phys 1949 157:445-62
Acid-Base Changes
1. Result: mild resp alkalosis approx 7.48
(blowing off CO )
2. After 1-2 days:
Kidneys respond with H+ conservation
and HCO - excretion
3. pH restored close to (but not = to) 7.40
(occurs at approx 1 week)
2
3
Circulatory System
• Sympathetic Stimulation:
– Increased HR, BP, inotropy
– Selective vasoconstriction (muscles, skin, viscera)
– SNS normalizes during acclimatization
Am J Cardiol 1990
(Operation Everest II)
65:1475-80
Hematological System
• Hypoxia causes erythropoietin release
• HCT usually 30% above sea level
• HCT’s above 75% not uncommon
Help Acclimatization
• Graded Ascent
– More difficult-easy to
travel eg: Lukla
• Fluids, high CHO diet
• Younger
– more susceptible
• Physically fit
– no protection
Help Acclimatization
Help Acclimatization
•
•
•
•
•
•
•
•
Vitamin C
Calcium Ascorbate
Siberian Ginseng extract
L-Tyrosine
Ginkgo Biloba extract
Schizandra extract
Ginger Root extract
Reishi Mushroom extract
Help Acclimatization
• Diamox
– causes renal bicarb excretion leading to metabolic
acidosis, increasing ventilation
– diuretic action decreases edema
– sulfa drug and side effects
CO2 + H2O
H2CO3
Carbonic Anhydrase
H+ + HCO2-
AMS
• Headache plus at least
one of the following:
– GI upset,
weakness/fatigue,
difficulty sleeping,
dizziness or lightheadedness
– Nausea, vomiting,
anorexia common
AMS
• Symptoms develop within a few hours
• Max intensity at 24-48 hours
• Symptom free at day 3-4
Aviat Space
Environ Med
1980;51:872-77
General Treatment of HA Problems
• Descent
• Portable hyperbaric
chamber
• Oxygen
• Specific medications
Gamow Bag
Mild
Moderate
Severe
•All symptoms mild
•Not alarming
•Symptoms more
intense
•Disrupting trip
•Alarming
•Worsening of s/s’s of
AMS
•Possibly altered mental
status
•Other HA illness may
be present
•Stay at current altitude
•Resume when
improved
•Tylenol for headache
•Compazine for N/V
•Consider descent but
not mandatory
•Diamox
•Resume when
improved
•Mandatory descent or
Gamow bag if cannot
walk
•Diamox
•Consider terminating
trip
High Altitude Cerebral Edema
• Continuum of AMS
• Brain swelling
• Hallmark symptoms:
– Ataxia, mental status
changes, confusion,
stupor, coma
Cerebral Edema?
HACE - Treatment
•
•
•
•
Early recognition required
Mandatory descent and evacuation
All general high altitude illness treatments
Dexamethasone 8 mg IM or IV then 4 mg
every 6 hours
• Prognosis good to deadly
HACE Case
HAPE
• Most common cause of death in HA
• Non-cardiogenic pulmonary edema
• At 14K on Denali:
– O2 sats in 56%
– Avg pO2 = 28
J Appl Physiol 64:2605,1988
HAPE Physiology
• Normally hypoxia/ischemia produces vasodilation
• In lungs, HYPOXIC VASOCONSTRICTION
HAPE CXR
• Patchy b/c of different
areas of hypoxia and
vasoconstriction,
relocation of blood
and therefore edema
• Normal heart
• No Kerley lines
HAPE Susceptibility
• People who have abnormally high PAP
• Possibly congenital reduced NO synthetase
HAPE Treatment
• Oxygen and descent usually sufficient
• If those not available, nifedipine
– Decreases pulmonary hypertension
– New drug?
High Altitude Medical Kit
• Meds:
–
–
–
–
Diamox – PO
Nifedipine – PO
Dexamethasone – IV
Ginko?
• Oxygen?
• Gamow bag?