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ALTITUDE MEDICINE

ALTITUDE MEDICINE. Shawn Dowling Sept 2008. Discuss basic altitude physiology How to recognize altitude disorders Management Prevention. Will not discuss: Subacute/Chronic Altitude Illnesses Cold-related illnesses Altitude-exacerbated illnesses. Objectives. High Altitude Illnesses.

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ALTITUDE MEDICINE

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  1. ALTITUDE MEDICINE Shawn Dowling Sept 2008

  2. Discuss basic altitude physiology How to recognize altitude disorders Management Prevention Will not discuss: Subacute/Chronic Altitude Illnesses Cold-related illnesses Altitude-exacerbated illnesses Objectives

  3. High Altitude Illnesses • Definition • Cerebral (AMS  HACE spectrum) and pulmonary (HAPE) syndromes which develop in un- or underacclimatized persons after ascent to high altitude • Are often PREVENTABLE and can usually be managed if S/Sx are recognized early and Tx are implemented in a timely fashion

  4. Moderate Altitude • 2400-3000m (8,000-10,000ft)- i.e. Lake Louise/Sunshine Valley • Minor impairment of arterial oxygen transport (SaO2>90%), PAO2>60 torr • Usually not clinically important unless significant underlying medical disorder • AMS common with rapid ascent above 2500 meters

  5. High Altitude • 3000-5500m (10,000-18,000ft) • i.e. Mount Columbia (12, 365ft – highest point in Alberta) • Maximum arterial saturation < 90%; PAO2<60 torr • Most common range for serious altitude illness

  6. Extreme Altitude • 5500-8850m (18,000-29,035ft) from Mount Logan (19550ft) to Mount Everest (29035ft) • Marked hypoxemia and hypocapnia • Maximum arterial saturation 50-75%; PAO2 28-40 torr • Deterioration eventually outstrips acclimatization, complete acclimatization not possible

  7. Epidemiology

  8. Holy Crap!!

  9. More About Gas! At sea level we are underneath an ocean of air % O2 is always 21% But as you climb higher, the Patm drops and thus your PO2 drops PiO2 = 0.21(PB-47) PB=barometric pressure At sea level PiO2= 160 mm Hg  At 2500m PiO2 = 119 mm Hg  Aconquilcha,Chile 5340m PiO2 = 82 mm Hg On top of Everest (8848m) PiO2 = 43 mm Hg  Thanks Rigby

  10. Acclimatization • 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/18150ft, beyond that progressive deterioration occurs

  11. So WHAT IS the problem with Altitude? • HYPOXIA • WHAT ARE THE PHYSIOLOGIC COMPENSATIONS? • Essentially all the physiologic changes are attempting to improve arterial and therefore cellular oxygenation

  12. Pulmonary Response to PiO2 • Hypoxemic Ventilatory Response • Begins w/i minutes of ascent above 1500m • Hypoxia - pulmonary vasoconstrictor • Allows for selective shunting away from areas of hypoxia w/preferential areas of vasodilation • pulmonary vascular resistance • pulmonary artery pressure (cold and exercise PAP while descent, O2 and certain Rx PAP) • diffusion capacity and lung volume

  13. Hypoxemic Ventilatory Response • Ventilation increases proportionally to the degree of hypoxia detected at the chemoreceptors • Lower PaCO2 = higher PAO2 • remember … PAO2 = PiO2 - PaCO2/R • As PCO2 drops a respiratory alkalosis occurs (what does this do to the medulla?) • kidneys compensate by excreting bicarb(over 6-8/7) • Vigourous HVR helps acclimatization whereas a poor HVR may lead to altitude-illness

  14. HVR Carotid bodies O2 Aortic bodies

  15. Cerebral Circulation • Hypoxemia = increases cerebral blood flow • Hypocapnea = decreases cerebral blood flow • Net result is an increase (modest) in cerebral blood flow at PaO2 <60 (altitude >12,500 feet) • Contributes to pathophysiology of AMS and HACE

  16. CVS Response • Catecholamine release: Epi and Norepi • Sympathetic Tone: • CO= HR x SV • BP= CO x PVR • This responses allows for better tissue perfusion (but, also decreases exercise performance) – over time epi/norepi levels drop and CO/HR/PVR return to normal

  17. Hematologic • Blood volume increases immediately: • Primarily due to hemo[ ] from diuresis • Hypoxia stimulates renal EPO production • Takes weeks for it to effect Red Cell Mass • Oxygen Dissociation curve – combination of inc 2,3 DPG (rightward shift) and alkalosis (leftward shift) leads to minimal net effect

  18. Acclimatization

  19. Gotta know it. It’ll be on the exam!

  20. High Altitude Illness • What are RF? • What are positive predictors? • What worsens altitude illnesses? • What does not effect altitude illnesses?

  21. High Altitude Illness • What are Risk Factors? • Rate of ascent/Starting altitude • Altitude reached • Sleeping at altitude • Individual physiology/Genetics? • What are Positive Predictors? • Hx of prior ascent w/o Sx • Elderly (less AMS/HACE), Women (less HAPE)

  22. What worsens altitude-illnesses? • Respiratory depressants/Alcohol • Pre-existing Medical Illnesses (very few): i.e. Pulm HTN, certain CHD, • Exertion • Hypothermia • What does not affect risk? • Physical fitness • CAD/HTN • Mild COPD • Pregnancy • DM

  23. Case #1 • You’ve decided to hike to Machu Picchu and have flown directly from Lima (sea level) into Cuzco (3515m/11,600ft). That day you start the hike up and notice you develop a nasty HA, and nausea.

  24. What’s your Diagnosis? • Acute Mountain Syndrome • High Altitude Cerebral Edema • High Altitude Pulmonary Edema • Other Medical Illness

  25. Pearl • Any illness at altitude is altitude illness until proven otherwise.

  26. Lake Louise Criteria for AMS • Presence of a HA in an un-acclimatized person who has arrived at an altitude >2000m (usu >2500m) • + 1 of • GI (anorexia, N,V) • Fatigue • Insomnia • Dizziness/lightheaded • Sx usually begin between 6-10 hrs but may be as early as 1 hour

  27. Pearls • Never ascend with symptoms of AMS • Never leave someone with AMS alone -Letting someone with AMS hike alone is the equilavent of going for a hike in the Kananaski’s alone the night of Party at the retreat.

  28. AMS Pathophysiology

  29. Treatment? • Any or Combination • Stop, Rest and Continue once Sx resolve • Acetazolimide (alone or in combination) • Dexamethasone • O2, immediate descent • Nifedipine • + Symptomatic Treatment

  30. Treatment? • Any or Combination • Stop, Rest and Continue once Sx resolve • Acetazolamide (alone or in combination) • Dexamethasone (if severe) • O2, rapid/immediate descent • Nifedipine • + Symptomatic Treatment

  31. Treatment Options of AMS • Stop and rest at altitude that Sx 1st develop +/- Acetazolamide -> May proceed once Sx abate • + Tx Sx • Nausea: Prochlorperazine 10mg po/im (stimulates HVR) • HA: Tylenol/NSAID’s • Insomnia: acetazolamide 125mg PO QHS

  32. Treatment of AMS Mild Symptoms Does not need descent if mild Sx and constant supervision Stop ascent until better Acetazolamide (250 BID) Tylenol/ASA for Sx Anti-emetic PRN Consider O2 at 1-2 LPM Moderate or Unresolving AMS Descent 500 m Consider: O2 at 1-2 LPM Hyperbaric therapy Dexamethasone 4mg PO q6h until able to descend May ascend after symptoms resolve

  33. If someone is getting worse, go down at once • If Sx of HACE are present DESCEND IMMEDIATELY

  34. Quick word about Acetazolamide • What’s the MOA?

  35. Quick word about Acetazolamide • What’s the MOA? • Causes a bicarb diuresis by inhibiting Carbonic Anhydrase at the kidney • This leads to a metabolic acidosis which counteracts the alkalosis from hyperventilation • Allowing an individual to have a better HVR and therefore acclimatize better • Which allergy must you ask about?

  36. Pt adamant that the HA is from dehydration • Can give Dx/Tx of 1L of fluid + advil or tylenol – if this completely resolves HA, not likely to be AMS

  37. Case #2 • Despite the advice to refrain from continuing to ascend, you continue up and begin to feel disoriented and noticed you seem to be walking with a drunken’ sort of gait • Dx?

  38. High Altitude Cerebral Edema (HACE) • Least common but most lethal altitude illness • Usually occurs above 3600m(12,000 feet) • Symptoms usually develop over 1-3 days • reported range 12 hours to 9 days • Usually also have symptoms of AMS / HAPE

  39. HACE Dx • Presence of a change in mental status and/or ataxia in a person with AMS Or • Presence of both mental status changes and ataxia in a person without AMS

  40. HACE S & Sx • Think of the effect of hypoxia and ICP • Global encephalopathy • Ataxia • Altered mentation • Seizures • Occasional CN palsies (secondary to increased ICP) • Papilledema • Retinal hemorrhage • Coma • Death is due to brain herniation

  41. HACE Pathophys

  42. Management?

  43. Tx of HACE • DESCENT (until pt improves) • O2 • DXM 8mg PO/IM/IV initially then 4mg Q6H • +/- acetazolamide 250mg PO BID • What if the weather does not allow for a safe descent and you happen to be part of a well equipped expedition?

  44. Protective Inflatable Toboggan?

  45. Gamow Bag • Hyperbaric Chambers • Lightweight (14.9 lb) • Manually pressurized • Generate 103mm Hg (2 psi) above ambient pressure • Simulates descent of 4000-5000 feet at moderate altitudes • Simulates descent of 9000 feet at top of Mt. Everest • After short course of treatment patient often able to descend on their own • This is primarily a temporizing measure - Not an alternate to descending

  46. Case #3 • During a visit to Nepal, Mr. Hackalung, decides to organize a hike to Everest Base camp (5430m/18000ft). • On day 3 you notice you notice he develops a dry cough and during the lunch break he’s quite SOB • You’re the group doc • What’s the most likely Dx?

  47. Fortunately for you, you realize that you develop X-ray vision at altitude – convenient skill – except that you’re on an all guy expedition but…- here is what you see. Case #3

  48. High Altitude Pulmonary Edema (HAPE) • Responsible for most high altitude deaths • Relatively Abrupt Onset • Usually occurs on 2nd night at altitude, Rare after 4 days • Women less susceptible than men • Presence of HAPE increases likelihood of cerebral illnesses – by worsening hypoxemia: 50% have AMS & 14% have HACE

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