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

Extreme18,000

Very High12,000

High8,000

Medium5,000

Low0

Acclimatization

• Definition: series of adaptations the body undergoes when exposed to high altitude for extended periods

• Fascinating and complex physiology

Altitudemeters

PBmm Hg

PIO2mm Hg

PaO2mm Hg

PaCO2mm 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

Lowlander

1. Base Camp2. To top ice fall then Base Camp3. Rest (Base Camp)4. Rest (Base Camp)5. Base Camp to Camp I6. Touch Camp II then back to Camp I7. Camp I to Base Camp8. Rest (Base Camp)9. Rest (Base Camp)10. Base Camp to Camp I11. Camp I to Camp II12. Rest (Camp II)13. Part way up Lhotse face then to Camp II14. Camp II to Base Camp15. Rest (Base Camp)16. Rest (Base Camp)17. Rest (Base Camp)18. Base Camp to Camp II19. Rest (Camp II)20. Camp II to Camp III21. Yellow Band then to Camp II22. Base Camp23. Wait for weather window

Lowlander

1. Base Camp2. To top ice fall then Base Camp3. Rest (Base Camp)4. Rest (Base Camp)5. Base Camp to Camp I6. Touch Camp II then back to Camp I7. Camp I to Base Camp8. Rest (Base Camp)9. Rest (Base Camp)10. Base Camp to Camp I11. Camp I to Camp II12. Rest (Camp II)13. Part way up Lhotse face then to Camp II14. Camp II to Base Camp15. Rest (Base Camp)16. Rest (Base Camp)17. Rest (Base Camp)18. Base Camp to Camp II19. Rest (Camp II)20. Camp II to Camp III21. Yellow Band then to Camp II22. Base Camp23. Wait for weather window

Sherpa

1. Base Camp2. Base Camp3. Base Camp4. Base Camp5. Base Camp6. Base Camp to Camp II7. Rest (Camp II)8. Base Camp9. Base Camp10. 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

Am J Phys 1949 157:445-62

Altitude (ft) Resp Rate Min Vent (L/min)

0 12 8

12,000 14 10

18,000 15 11

24,000 27 23

Acid-Base Changes

1. Result: mild resp alkalosis approx 7.48 (blowing off CO2)

2. After 1-2 days: Kidneys respond with H+ conservation and HCO3

- excretion

3. pH restored close to (but not = to) 7.40 (occurs at approx 1 week)

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 H+ + HCO2-

Carbonic Anhydrase

AMS

• Headache plus at least one of the following:– GI upset,

weakness/fatigue, difficulty sleeping, dizziness or light-headedness

– 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?