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Military Sports Medicine Fellowship. High Altitude: Physiology & Illness. “Every Warrior an Athlete”. Kevin deWeber , MD, FAAFP, FACSM COL, US Army Director, Military Sports Medicine Fellowship 2012. Objectives. Outline strategies to optimize exercise performance at altitude
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Military Sports Medicine Fellowship High Altitude:Physiology & Illness “Every Warrior an Athlete” Kevin deWeber, MD, FAAFP, FACSM COL, US Army Director, Military Sports Medicine Fellowship 2012
Objectives • Outline strategies to optimize exercise performance at altitude • Review pathophysiology of high altitude illness (HAI) • Review the types of HAI and how they are treated • Review factors predisposing to HAI • Discuss factors in return-to-altitude decisions after HAI
Cuenca, Ecuador • 8,400 ft (2560 m)
Preview • Acclimatization and slow ascent are powerful preventives for High Altitude Illness • Acclimatize properly • Spend 2-3 nights at 2500-3000m before ascent • Slow ascent • Ascend < 500 m/day of sleeping altitude • Rest day every 3-4 days • Prophylactic meds advised if unable to comply • Acetazolamide is powerful to prevent most HAI • Dexamethasone powerfully treats serious HAI
Preview: RISK of HAI • Low risk: • No prior h/o HAI and ascent to <2800m (9180 ft) • Taking >= 2 days to ascend to 2500-3000m (8200-9840 ft) AND sleeping altitude increases <500m/d Luks et al. Wilderness Medicine Society consensus guidelines for prevention and Treatment of acute altitude illness. Wilderness Envir Med 2010.
Moderate risk of HAI: • Prior h/o AMS and ascending to 2500-2800m in 1 day (8200-9180 ft) • NO prior h/o AMS but ascending to >2800m in 1 day • ALL ascending >500m/d (sleep elev.) at >3000m
High risk of HAI • Prior h/o AMS and ascending to >2800m in 1 day • ALL with prior h/o HACE or HAPE • ALL ascending to >3500m (11480 ft) in 1 day • ALL ascending >500m/d (sleep elev.) at >3500m • Very rapid ascents (e.g. Mt. Kilamanjaro)
Preview: Prevention of HAI • Moderate and High risk persons: consider prophylactic meds • PRIMARY: Acetazolamide 125 mg bid • Start 2d prior to ascent, stop 2-3d after summit • Kids: 2.5 mg/kg/d • ALT: Dexamethasone 2mg QID or 4mg BID • Only if can’t tolerate Acetazolamide • Start day of ascent, stop 2-3d after summit • Ibuprofen 600 mg tid (two studies) Luks et al. Wilderness Medicine Society consensus guidelines for prevention and Treatment of acute altitude illness. Wilderness Envir Med 2010.
Environment at high altitude(>1500 m or 4920 ft) • Barometric pressure decreases • Partial pressure of oxygen decreases • “Hypobaric Hypoxia” • Lower alveolar O2 leads to lower SaO2
Effects of High Altitude Exposure • Decreased exercise capacity • +/- 1% decrease in VO2max per 100m above 1500m • Individual variability • MECHANISMS: • Peripheral hypoxia • Cerebral hypoxia peripheral inhibition • High altitude illness • Individual variability
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, hemoconcentration • Remodeling of pulmonary arterioles
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
Acute Mountain Sickness (AMS) • Occurs above 1500 m (4920 ft) • More common above 2500 m • Defined as HEADACHE plus one or more symptom: • Anorexia, nausea or vomiting • Fatigue or weakness • Dizziness or lightheadedness • Difficulty sleeping • Headache alone: High-Altitude Headache • Gabapentin, Acetazolamide, or Ibuprofen preventative • J Neurol Neurosurg Psychiat 2008 • Cephalgia 2007 • Wilderness Environ Med 2010
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
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
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
High Altitude Pulmonary Edema(HAPE) • CXR findings • Blotchy fluffy infiltrates • Pathophysiology Hypoxia pulmonary artery hypertension • alveolar damage edema and hemorrhage into alveoli
Risk factors for HAI • Rapid gain in altitude • Prior history of HAI • genetic factors involved • Alcohol, sedatives • Strenuous exercise • HAPE: cold ambient temperature, resp. infxn
HAI Protective Factors • Residence at elevation >900 m (2950 ft) • Slow gain in elevation • <500 m (1640 ft) per day in sleeping elevation • Genetic factors • Physical fitness NOT protective
Treating HAI:General Principles • Rest, halt ascent • Descend • Moderate AMS: >500 m (1640 ft) • HACE/HAPE: > 1000 m (3280 ft) • Oxygen if available (keep Pox >90%) • Keep warm (esp. for HAPE)
Treating HAI:Medications • Acetazolamide • Speeds acclimatization • Treats moderate AMS & HACE • Dose: 125-250 mg BID • Anti-emetics • Non-narcotic analgesics
Meds (cont.) • Dexamethasone • Decreases cerebral edema • Treats moderate AMS and HACE • Prevents AMS, HACE, HAPE • Dose • 8-16 mg/d in div doses
Meds (cont.) • Nifedipine • Decreases pulmonary artery pressure • Prevents HAPE • Dose: 30 mg SR BID (one study) • NOT EFFECTIVE FOR TREATMENT (one study)
Meds (cont.) • Salmeterol • Decreases alveolar fluid transport • May prevent HAPE • Dose: 125 mcg inhaled BID
Meds (cont.) • Tadalafil • Dilates pulmonary vessels, prevents pulmonary hypertension • May prevent HAPE • Dose: 10 mg po BID
Treatment of AMS • Descend > 500 m (1640 ft) OR • Rest 1-2 days at same altitude • Oxygen 12-24 hours, if available • Symptomatic treatment with analgesics, anti-emetics • Consider acetazolamide 125-250 mg po BID
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 • Consider adding acetazolamide • Portable hyperbaric therapy if descent impossible
Portable Hyperbaric Chambers
Treatment of HAPE • Immediate descent >1000 m • Oxygen to keep SaO2 >90%. • If descent/O2 not immediately available… • Portable hyperbaric therapy • Nifedipine 30 mg extended release BID (avoid if concomitant HACE) and • Salmeterol 125 mcg inhaled
Prevention of HAI:General Principles • Proper acclimatization protocols are paramount • Avoid abrupt ascent to >3000 m (9843 ft) • Spend 2-3 nights at 2500-3000 m before ascending further • Ascend no more than 500 m (1640 ft) per day in sleeping altitude when >2500 m (8200 ft) • Rest day every 3-4 days
Prevention of HAI:Other protective factors • Living at altitude >2200 m days to weeks • >5days above 3000m last 2 months --> less AMS (Schneider et al, MSSE 2002) • Intermittent Hypoxic Exposure (IHE) 4hr/d x15d less AMS @4300 m • Beidleman et al, Clin Sci 2004
Prevention of HAI:FIRST DETERMINE RISK • Low risk: • No prior h/o HAI and ascent to <2800m (9180 ft) • Taking >= 2 days to ascend to 2500-3000m (8200-9840 ft) AND sleeping altitude increases <500m/d Luks et al. Wilderness Medicine Society consensus guidelines for prevention and Treatment of acute altitude illness. Wilderness Envir Med 2010.
Cuenca, Ecuador • 8,400 ft (2560 m)
Moderate risk of HAI: • Prior h/o AMS and ascending to 2500-2800m in 1 day (8200-9180 ft) • NO prior h/o AMS but ascending to >2800m in 1 day • ALL ascending >500m/d (sleep elev.) at >3000m
High risk of HAI • Prior h/o AMS and ascending to >2800m in 1 day • ALL with prior h/o HACE or HAPE • ALL ascending to >3500m (11480 ft) in 1 day • ALL ascending >500m/d (sleep elev.) at >3500m • Very rapid ascents (e.g. Mt. Kilamanjaro)
Prevention of AMS/HACE • Moderate and High risk persons: consider prophylactic meds • PRIMARY: Acetazolamide 125 mg bid • Start 2d prior to ascent, stop 2-3d after summit • Kids: 2.5 mg/kg/d • ALT: Dexamethasone 2mg QID or 4mg BID • Only if can’t tolerate Acetazolamide • Start day of ascent, stop 2-3d after summit • Ibuprofen 600 mg tid (two studies) Luks et al. Wilderness Medicine Society consensus guidelines for prevention and Treatment of acute altitude illness. Wilderness Envir Med 2010.
Prevention of AMS/HACE SPECIAL SCENARIOS • Military Ops requiring exertion and >3500m: • Dexamethasone (also increases VO2max)
Prevention of HAPE • ALL: ascent/rest precautions • Moderate/High risk: consider meds: • PRIMARY: Acetazolamide 125 mg BID • PRIOR HAPE: Nifedipine 60 mg SR daily + Salmeterol 125 mcg BID • ALTERNATE: Tadalafil 10 mg BID or Dexamethasone 16 mg/d divided doses Luks et al. Wilderness Medicine Society consensus guidelines for prevention and Treatment of acute altitude illness. Wilderness Envir Med 2010.
Considerations for high-altitude activities in those with prior HAI • Risk level • Severity and type of prior HAI • Ascent requirements • Feasibility of descent/extra rest days if needed • Availability of medical treatments