High Altitude:High Altitude:Physiology & IllnessPhysiology & Illness

Kevin deWeber, MD, FAAFP, FACSMKevin deWeber, MD, FAAFP, FACSMCOL, US ArmyCOL, US Army

Director, Military Sports Medicine FellowshipDirector, Military Sports Medicine Fellowship20122012

MilitarySports Medicine

Fellowship

“Every Warrior an Athlete”

ObjectivesObjectives

• 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, EcuadorCuenca, Ecuador

• 8,400 ft (2560 m)

PreviewPreview

• 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

• 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

Preview: RISK of HAIPreview: RISK of HAI

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 HAIPreview: 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 altitudeEnvironment at high altitude(>1500 m or 4920 ft)(>1500 m or 4920 ft)

• Barometric pressure decreases

• Partial pressure of oxygen decreases

• “Hypobaric Hypoxia”– Lower alveolar O2

leads to lower SaO2

Effects of Effects of High Altitude ExposureHigh 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 = body’s adaptation Acclimatization = body’s adaptation to hypobaric hypoxiato hypobaric hypoxia

AcclimatizationAcclimatization

• 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

Altitude Illnesses Altitude Illnesses (Failure to Acclimatize)(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

Acute Mountain Sickness (AMS)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 performanceEffects 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 EdemaHigh Altitude Cerebral Edema(HACE)(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 EdemaHigh Altitude Pulmonary Edema(HAPE)(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 EdemaHigh Altitude Pulmonary Edema(HAPE)(HAPE)

• CXR findings– Blotchy fluffy infiltrates

• PathophysiologyHypoxia

pulmonary artery hypertension

alveolar damage edema and

hemorrhage into alveoli

Risk factors for HAIRisk 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 FactorsHAI 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:Treating HAI:General PrinciplesGeneral 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:Treating HAI:MedicationsMedications

• Acetazolamide– Speeds acclimatization– Treats moderate AMS & HACE– Dose: 125-250 mg BID

• Anti-emetics• Non-narcotic analgesics

Meds (cont.)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.)Meds (cont.)

• Nifedipine– Decreases pulmonary artery

pressure– Prevents HAPE

• Dose: 30 mg SR BID (one study)

– NOT EFFECTIVE FOR TREATMENT (one study)

Meds (cont.)Meds (cont.)

• Salmeterol– Decreases alveolar fluid

transport– May prevent HAPE– Dose: 125 mcg inhaled BID

Meds (cont.)Meds (cont.)

• Tadalafil– Dilates pulmonary vessels,

prevents pulmonary hypertension

– May prevent HAPE– Dose: 10 mg po BID

Treatment of AMSTreatment 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 HACETreatment 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

PortableHyperbaricChambers

Treatment of HAPETreatment 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 PREVENTION OFOFHAIHAI

Prevention of HAI:Prevention of HAI:General PrinciplesGeneral 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:Prevention of HAI:Other protective factorsOther 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

• 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

Prevention of HAI:Prevention of HAI:FIRST DETERMINE RISKFIRST DETERMINE RISK

Luks et al. Wilderness Medicine Society consensus guidelines for prevention and Treatment of acute altitude illness. Wilderness Envir Med 2010.

Cuenca, EcuadorCuenca, 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/HACEPrevention 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 Prevention of AMS/HACE SPECIAL SCENARIOSSPECIAL SCENARIOS

• Military Ops requiring exertion and >3500m:

• Dexamethasone (also increases VO2max)

Prevention of HAPEPrevention 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 Considerations for high-altitude activities in those with prior HAIactivities 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

Questions?Questions?