High Altitude Medicine

1. High Altitude Medicine Scott McIntosh, MD, MPH Director, EMS/Wilderness Medicine Fellowship University of Utah

4. Connecticut

5. Why study? • Live in or travel to high areas

6. Why study? • Live in or travel to high areas • Excellent physiology

7. Why study? • Live in or travel to high areas • Excellent physiology • Expedition medical director

9. 14,000 ft Camp

10. The Plan • Definitions • Acclimatization - by system • Specific problems: • Acute Mountain Sickness (AMS) • High Altitude Cerebral Edema (HACE) • High Altitude Pulmonary Edema (HAPE)

11. How high is high? 29,000 Extreme 18,000 Very High 12,000 High 8,000 Medium 5,000 Low 0

13. Acclimatization • Definition: series of adaptations the body undergoes when exposed to high altitude for extended periods • Fascinating and complex physiology

15. Map of Everest

17. Acclimatization physiology

18. Acclimatization schedules Lowlander • 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

19. Acclimatization schedules Lowlander • 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 • 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

20. Respiratory • Hypoxic Ventilatory Response • Carotid bodies sense decreased pO2 • Central medullary receptors sense pH changes (CO2 diffuses across, dropping pH) • Response is genetically predetermined • South American vs. Himalayan natives

21. Hypoxic Ventilatory Response Am J Phys 1949 157:445-62

22. Acid-Base Changes • Result: mild resp alkalosis approx 7.48 (blowing off CO2) • After 1-2 days: Kidneys respond with H+ conservation and HCO3- excretion • pH restored close to (but not = to) 7.40 (occurs at approx 1 week)

25. 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

26. Hematological System • Hypoxia causes erythropoietin release • HCT usually 30% above sea level • HCT’s above 75% not uncommon

27. Help Acclimatization • Graded Ascent • More difficult-easy to travel eg: Lukla • Fluids, high CHO diet • Younger • more susceptible • Physically fit • no protection

28. Help Acclimatization

29. Help Acclimatization • Vitamin C • Calcium Ascorbate • Siberian Ginseng extract • L-Tyrosine • Ginkgo Biloba extract • Schizandra extract • Ginger Root extract • Reishi Mushroom extract

30. 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

31. AMS • Headache plus at least one of the following: • GI upset, weakness/fatigue, difficulty sleeping, dizziness or light-headedness • Nausea, vomiting, anorexia common

32. 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

33. General Treatment of HA Problems • Descent • Portable hyperbaric chamber • Oxygen • Specific medications

34. Gamow Bag

35. Characteristics Treatment

36. High Altitude Cerebral Edema • Continuum of AMS • Brain swelling • Hallmark symptoms: • Ataxia, mental status changes, confusion, stupor, coma

37. Cerebral Edema?

38. 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

39. HACE Case

41. 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

42. HAPE Physiology • Normally hypoxia/ischemia produces vasodilation • In lungs, HYPOXIC VASOCONSTRICTION

43. HAPE CXR • Patchy b/c of different areas of hypoxia and vasoconstriction, relocation of blood and therefore edema • Normal heart • No Kerley lines

44. HAPE Susceptibility • People who have abnormally high PAP • Possibly congenital reduced NO synthetase

45. HAPE Treatment • Oxygen and descent usually sufficient • If those not available, nifedipine • Decreases pulmonary hypertension • New drug?

46. High Altitude Medical Kit • Meds: • Diamox – PO • Nifedipine – PO • Dexamethasone – IV • Ginko? • Oxygen? • Gamow bag?