High Altitude Medical Problems

1. High Altitude Medical Problems • Resident Rounds • Garth Smith R3 • Feb 25, 2010 • thanks to Shawn Dowling, Chris Hall

2. Objectives • Review some physiology and terminology • Recognition, Treatment, Risk Factors, and Prevention of High Altitude Syndromes • high altitude decompression of airplanes • secretly make use of the Gas Laws • Not covering Illnesses Aggravated by High Altitude, hypothermia, trauma, frostbite, avalanches, lightning

3. Case 1 • 24y male trekking with friends • 20-night trek including a pass @ 5,400m • During 8th day c/o headache at dinner (4,000m) • Has poor sleep but awakes feeling well enough to continue • Continues hiking and by mid-morning has H/A again and has vomited twice (now at 4,150m)

4. Case 2 • 20yo male porter • Camped at 4,930m after crossing a steep, technical pass at 5,120m and awoke with significant exercise intolerance and a cough • Descended with the group and camped at 3,800m feeling significant improvement • The following morning had severe dyspnea at rest; was unable to carry his load • Arrives at a volunteer clinic being carried by his colleagues; resting O2 sat 48% on room air

5. Summary • go up slow, sleep low, take it easy, consider taking meds prophylactically if at risk • if kinda sick: find a friend, rest, don’t ascend, and consider meds. ascend when no symptoms. • if sick: find a friend, descend, and use meds. • if really sick: a friend will find you, they will get you down fast, and they will use meds on you. • oxygen is good. portable HBOT is wise. • the mountain will be there tomorrow.

6. What mtn am I on?

7. How high is high? • intermediate • 1500-2500m • high • 2500 - 4200m • very high • 4200 - 5500m • extreme • >5500m • “dead zone” • >7600m

8. Who wrote this book?

9. Who is this guy?

10. What’s the problem • High altitude is a hypoxic environment! • hypoxia is bad • we need oxygen to live

11. What is the concentration of oxygen at sea level? 5000m above sea level?

12. same volume same temp same concentration but twice the mass = ? x pressure both have 21% O2 but I’d get more O2 on the right if delivered at twice the pressure Hey...we just used the ideal gas law

13. Gas Laws • Boyle’s Law • Dalton’s Law • Henry’s Law the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid

14. Hypoxia • Partial pressure of oxygen decreases as a function of the barometric pressure Hey...we just used Dalton’s law!

15. What SaO2% or PaO2 makes you worried?

16. Hypoxemia What’s the problem • High altitude is a hypoxic environment because of hypoxemia

17. If PaO2 is halved when Barometric Pressure is doubled, why isn’t SaO2% halved?

18. 75

19. Below what Osat would someone rapidly deteriorate and become unconscious?

20. 75 60

21. Why is the pressure lower at altitude? Pressure = force / area more mass = more force = more pressure

22. What happens when you are exposed to low PiO2 • increased ventilation • make more blood • diuresis • ↑sympathetic tone • ↑pulmonary pressure improve arterial and cellular oxygenation

23. Ventilation • hypoxic ventilatory response (HVR) • effected by the carotid body - senses ↓paO2 • resp center in medulla ↑RR • effected by chronic hypoxia, ETOH, resp suppresants (benzos, opiods) • culminates after 4 -7 d • central chemoreceptors reset to progressively lower PCO2

24. Acclimatization • The process by which individuals gradually adjust to hypoxia and enhance survival and performance • Complex adaptation by essentially every system to minimize hypoxia and maintain cellular functions despite decreased PiO2 • Given sufficient time most people can acclimatize to 5500m, beyond that progressive deterioration occurs

25. Definition • “high-altitude illness” (HAI) is used to describe the cerebral and pulmonary syndromes that can develop in unacclimatized persons shortly after ascent to high altitude. HAPE AMS → HACE

26. Pathophysiology

27. Name 4 risk factors for the development of HAI

28. Risk factors • fast ascent, high altitude reached, high sleeping altitude • a history of HAI • residence at an altitude below 900 m • physical exertion, cold • preexisting pulmonary hypertension, low hypoxic ventilatory response and low vital capacity

29. Epidemiology • age has little influence on incidence but persons >50 may have some protection • physical fitness has no bearing on susceptibility to HAI • women are equally at risk for AMS/HACE but less susceptible to HAPE • HAI is reproducible in an individual on repeated exposures; suggesting some unknown genetic risk factors

30. I’ll never see that...

31. AMS → HACE • Acute Mountain Sickness (AMS) and High Altitude Cerebral Edema (HACE) are considered a spectrum of the same pathophysiological process • HACE is the end-stage of AMS.

32. what three criteria must be met in all cases of AMS?

33. AMS • Lake Louise Consensus Group says • AMS is • 1) headache in • 2) unacclimatized person • 3) at altitude >2500m • 4) plus one or more of: GI symptoms, insomnia, dizziness, lassitude, or fatigue

34. HACE • defined as the onset of ataxia, altered consciousness (drowsiness is commonly followed by stupor), or both in someone with acute mountain sickness or high-altitude pulmonary edema. • In those who also have high-altitude pulmonary edema (HAPE), severe hypoxemia can lead to rapid progression from acute mountain sickness to high-altitude cerebral edema. • The cause of death is brain herniation.

35. AMS → HACE Pathophysiology

36. Name 4 classes of medications used in the treatment of AMS → HACE

37. Prophylaxis • ASA 325 Q4 x 3 dose (HA only) • Acetazolamide 125-250 BID • slow ascent • meds not for everyone (risk of unknown sulfa allergy) • consider if prev history of AMS at low/mod altitude, or forced rapid ascent (flying to high elevation)

38. Treatment • Mild Symptoms of AMS • Does not need descent if mild Sx and constant supervision • Stop ascent until better • Acetazolamide (250 BID) • Tylenol/ASA/NSAID for HA • Anti-emetic PRN • Consider O2(1-2L) • May ascend after Sx resolve • Avoid things that limit HVR • Moderate or Unresolving AMSDescend 500 m, if not possibleO2 at 1-2 LPMHyperbaric therapyDexamethasone 4mg PO/IV/IM q6h • Acetazolamide (250 BID)May ascend after symptoms resolve

39. Treatment • HACE • Initiate immediate descent or evacuation • if descent is not possible, use a portable hyperbaric chamber • administer oxygen (2 to 4 liters/min) • administer dexamethasone (8 mg orally, intramuscularly, or intravenously initially, and then 4 mg every 6 hr) • administer acetazolamide if descent is delayed

40. Rebound • Acetazolamide “cures” AMS, discontinuation does not risk rebound of symptoms, unless you climb higher • Dexamethasone improves AMS→HACE but does not cure it. discontinuation can induce rebound symptoms and clinical deterioration even at constant altitude

41. Gamow Bag

42. Portable Hyperbaric Chamber • pronounced “Gam-Off”, Dr. Igor Gamow • Lightweight (14.9 lb), costly ($2400US) • Manually pressurized • Generate 100mm Hg above ambient pressure • Simulates descent of 1,500m at moderate altitudes • After short course of treatment patient often able to descend on their own • duration - AMS - 2 hrs, HAPE - 4hrs, HACE - 6hrs • This is primarily a temporizing measure - Not an alternate to descending

43. Hypoxemia What’s the problem

44. Dr. Gamow’s father George was a famous physicist. What did theory did he co-author

45. How does acetazoladmide help with AMS → HACE?

46. AMS → HACE Pathophysiology

47. How does dexamethasone help with AMS → HACE?

48. AMS → HACE Pathophysiology

49. Myths • Coca leaves for Machu Picchu • Ginko Baloba helps/prevents • overhydration prevents

50. HAPE • High Altitude Pulmonary Edema (HAPE) • this is the killer - accounts for most deaths from high-altitude illness • commonly strikes the second night at a new altitude (sneaky) • rarely occurs after more than four days at a given altitude