High Altitude Illness

1. High Altitude Illness Kevin deWeber, MD, FAAFP Lieutenant Colonel, US Army Army World Class Athlete Program Ft. Carson, CO

3. Objectives • Review pathophysiology of high altitude illness (HAI) • Review the types of HAI and how they are treated • Review factors predisposing to HAI • Discuss preventive treatment for those with a remote history of HAI

4. Preview • Acclimatization and slow ascent are powerful • Ascend < 600 m/day • Rest day every 600 – 1200 m • Prophylactic meds advised if unable to comply • Treatment: rest, descent, oxygen, meds

5. Environment at high altitude(>1500 m or 4920 ft) • Barometric pressure decreases • Partial pressure of oxygen decreases • RESULT: “Hypobaric Hypoxia” • Lower alveolar O2 leads to lower SaO2

6. Ft. Carson, CO, ~6500 ft Pikes Peak, 14,110 ft (4300 m) US Air Force Academy, ~7,000 ft

7. Acclimatization = body’s adaptation to hypobaric hypoxia

8. Acclimatization • Immediate (minutes to hours) • ↑ Sympathetic tone ↑ HR & CO • ↑ Ventilation  ↑ PaO2 and↓ PaCO2  ↓ pH • Renal bicarbonate diuresis (to balance pH) • ↑ Pulmonary artery pressure ↑ O2 absorption • Delayed (days to weeks) • Erythropoietin  ↑ RBC production • Remodeling of pulmonary arterioles

9. Altitude Illnesses (Failure to Acclimatize) • Cerebral Syndromes • Acute Mountain Sickness (AMS) • High Altitude Cerebral Edema (HACE) mild AMS moderate AMS HACE • Pulmonary Syndrome • High Altitude Pulmonary Edema (HAPE) • Importance • HACE and HAPE can be fatal

10. Acute Mountain Sickness(AMS) • Defined as HEADACHE plus one or more symptom: • Anorexia, nausea or vomiting • Fatigue or weakness • Dizziness or lightheadedness • Difficulty sleeping

11. Effects of AMS on performance • Mild: annoyance only • Moderate: impaired concentration, memory, speech, and physical performance; • Can be disabling • Subtle abnormalities visible on MRI • Effects can last weeks

12. High Altitude Cerebral Edema(HACE) • AMS symptoms plus ALTERED L.O.C. and ATAXIA • Other neuro findings possible • Coma develops • Death results if untreated • Pathophysiology • altered cerebral vascular permeability leads to brain swelling • MRI: cerebral edema, lesions of corpus callosum

13. High Altitude Pulmonary Edema(HAPE) • Defined by two pulmonary symptoms… • Cough, dyspnea at rest, exercise intolerance, chest tightness/congestion… • and two pulmonary signs… • Crackles, wheezing, cyanosis, tachypnea, tachycardia • Most common cause of death among HAI • 50% mortality rate if not treated quickly

14. High Altitude Pulmonary Edema(HAPE) • CXR findings • Blotchy fluffy infiltrates • Pathophysiology Hypoxia  pulmonary artery hypertension • alveolar damage  edema and hemorrhage into alveoli

15. Risk factors for HAI • Rapid gain in altitude • Prior history of HAI • genetic factors involved • Alcohol, sedatives • HAPE: cold ambient temperature

16. HAI Protective Factors • Residence at elevation >900 m (2950 ft) • Slow gain in elevation • <600 m (1970 ft) per day in sleeping elevation • Genetic factors • Physical fitness NOT protective

17. Treating HAI • Rest, halt ascent • Descent • Moderate AMS: >500 m (1640 ft) • HACE: > 1000 m (3280 ft) • HAPE: 500 – 1000 m • Oxygen if available • Keep warm (esp. for HAPE) • Portable hyperbaric chambers

18. Portable Altitude Chamber® (PAC) Gamow® bag Certec® bag

19. Treating HAI (cont.) • Acetazolamide • Speeds acclimatization • 75% effective in preventing AMS • Treats moderate AMS & HACE • Dose: 125-250 mg BID

20. Treating HAI (cont.) • Dexamethasone • Decreases cerebral edema • Treats moderate AMS and HACE • Prevents AMS, ? HACE • Dose • 2 mg po/IM/IV QID • 4 mg BID

21. Treating HAI (cont.) • Nifedipine • Decreases pulmonary artery pressure • Prevents and treats HAPE • Dose: 20 – 30 mg extended release BID

22. Treating HAI (cont.) • Salmeterol • Decreases alveolar fluid transport • Prevents and treats HAPE • Dose: 125 mcg inhaled BID

23. Treating HAI (cont.) • Tadalafil • Dilates pulmonary vessels, prevents pulmonary hypertension • May prevent HAPE • Dose: 10 mg po BID

24. “Acute mountain sickness: influence of susceptibility, preexposure, and ascent rate” Schneider M et al. Med Sci Sports Exerc 2002

25. Treatment of Mild AMS • Descend > 500 m (1640 ft) OR • Rest 1-2 days at same altitude • Oxygen 12-24 hours, if available • Consider acetazolamide 125-250 mg po BID • Symptomatic treatment with analgesics, anti-emetics

26. Treatment of Moderate AMS • Descend >500 m • Rest 1-2 days • Do not allow continued ascent/activity • Significant performance/cognition decrement • Risk of progression to HACE • Oxygen 1-2 days, if available • Acetazolamide; dex as alternate

27. Prevention of recurrent AMS • Proper acclimatization, slow ascent. If not possible… • Acetazolamide 125-250 mg po BID starting 1 day prior to ascent, continuing until at max altitude for 2 days. If not possible… • Alternate: Dexamethasone 2 mg po QID or 4 mg BID, starting 1 day prior, cont. until at max altitude 2 days • Unknown which is better or if combination therapy is indicated

28. Treatment of HACE • Immediate descent > 1000 m and hospitalize • Oxygen to maintain SaO2 >90% • Dexamethasone—8 mg PO/IM/IV initially followed by 4 mg QID • Portable hyperbaric therapy if descent impossible

29. Treatment of HACE (cont.) • Management of coma • Bladder catheterization • Airway control • Diagnostic studies • CXR to rule out concurrent HAPE • MRI to rule out other conditions

30. Recovery from HACE:highly variable • 1-3 days for symptoms to resolve • Days to 12 weeks for neuropsychological function to normalize • 3-4 weeks for papilledema to resolve • Days to 5 weeks for MRI to normalize

31. Prevention of recurrent HACE (No evidence-based recommendations) • Strong recommendation for acclimatization and slow ascent. If not possible, or descent/medical treatment not possible… • Prophylaxis with acetazolamide or dexamethasone, as for AMS

32. Treatment of HAPE • Immediate descent 500-1000 m • Oxygen to keep SaO2 >90%. • If descent/O2 not immediately available… • Portable hyperbaric therapy • Nifedipine 20-30 mg extended release BID (avoid if concomitant HACE) and/or… • Salmeterol 125 mcg inhaled

33. Treatment of HAPE (cont.) • Admit if: • >4L/min O2 requirement • Elderly, very young • Concomitant HACE or co-morbid cardio-pulmonary disease • Dexamethasone if concomitant HACE • Low-flow outpatient O2for others; check daily

34. Recovery from HAPE • Variable; little evidence in literature • May take 2 weeks to recover strength • Resume some activity when SaO2 > 90% without supplemental O2 • Remaining at some altitude fosters acclimatization via pulmonary arteriolar remodeling

35. Prophylaxis for recurrent HAPE • Strong recommendation for acclimatization and slow ascent. If not possible, or descent/medical treatment not possible… • Prophylactic options: • Acetazolamide 125-250 mg po BID • Salmeterol 125 mcg inhaled BID • Nifedipine 20-30 mg extended release BID • Dexamethasone 8 mg po BID (one DBPC study) • Tadalafil 10 mg po BID (one DBPC study) • No evidence of superiority of one agent or risks/benefits of combination therapy

36. Preview • Acclimatization and slow ascent are powerful • Ascend < 600 m/day • Rest day every 600 – 1200 m • Prophylactic meds advised if unable to comply • Treatment: rest, descent, oxygen, meds

37. Thank you!