altitude medicine shawn dowling sept 2008 shawn dowling sept 2008

65
ALTITUDE MEDICINE Shawn Dowling Shawn Dowling Sept 2008 Sept 2008

Post on 20-Dec-2015

231 views

Category:

Documents


1 download

TRANSCRIPT

ALTITUDE MEDICINEALTITUDE MEDICINE

Shawn DowlingShawn DowlingSept 2008Sept 2008

Shawn DowlingShawn DowlingSept 2008Sept 2008

ObjectivesObjectives

Discuss basic Discuss basic altitude physiologyaltitude physiology

How to recognize How to recognize altitude disordersaltitude disorders

Management Management PreventionPrevention

Discuss basic Discuss basic altitude physiologyaltitude physiology

How to recognize How to recognize altitude disordersaltitude disorders

Management Management PreventionPrevention

Will not discuss:Will not discuss: Subacute/Chronic Subacute/Chronic

Altitude IllnessesAltitude Illnesses Cold-related Cold-related

illnessesillnesses Altitude-exacerbated Altitude-exacerbated

illnessesillnesses

Will not discuss:Will not discuss: Subacute/Chronic Subacute/Chronic

Altitude IllnessesAltitude Illnesses Cold-related Cold-related

illnessesillnesses Altitude-exacerbated Altitude-exacerbated

illnessesillnesses

High Altitude IllnessesHigh Altitude Illnesses

DefinitionDefinition Cerebral (AMS Cerebral (AMS HACE spectrum) and HACE spectrum) and

pulmonary (HAPE) syndromes which pulmonary (HAPE) syndromes which develop in un- or underacclimatized develop in un- or underacclimatized persons after ascent to high altitudepersons after ascent to high altitude

Are often PREVENTABLE and can usually Are often PREVENTABLE and can usually be managed if S/Sx are recognized early be managed if S/Sx are recognized early and Tx are implemented in a timely fashionand Tx are implemented in a timely fashion

DefinitionDefinition Cerebral (AMS Cerebral (AMS HACE spectrum) and HACE spectrum) and

pulmonary (HAPE) syndromes which pulmonary (HAPE) syndromes which develop in un- or underacclimatized develop in un- or underacclimatized persons after ascent to high altitudepersons after ascent to high altitude

Are often PREVENTABLE and can usually Are often PREVENTABLE and can usually be managed if S/Sx are recognized early be managed if S/Sx are recognized early and Tx are implemented in a timely fashionand Tx are implemented in a timely fashion

Moderate Altitude Moderate Altitude

2400-3000m (8,000-10,000ft)- i.e. Lake 2400-3000m (8,000-10,000ft)- i.e. Lake Louise/Sunshine Valley Louise/Sunshine Valley

Minor impairment of arterial oxygen transport Minor impairment of arterial oxygen transport (S(SaaOO22>>90%), P90%), PAAOO22>60 torr>60 torr Usually not clinically important unless significant Usually not clinically important unless significant

underlying medical disorderunderlying medical disorder AMS common with rapid ascent above 2500 AMS common with rapid ascent above 2500

metersmeters

2400-3000m (8,000-10,000ft)- i.e. Lake 2400-3000m (8,000-10,000ft)- i.e. Lake Louise/Sunshine Valley Louise/Sunshine Valley

Minor impairment of arterial oxygen transport Minor impairment of arterial oxygen transport (S(SaaOO22>>90%), P90%), PAAOO22>60 torr>60 torr Usually not clinically important unless significant Usually not clinically important unless significant

underlying medical disorderunderlying medical disorder AMS common with rapid ascent above 2500 AMS common with rapid ascent above 2500

metersmeters

High AltitudeHigh Altitude

3000-5500m (10,000-18,000ft) 3000-5500m (10,000-18,000ft) i.e. Mount Columbia (12, 365ft – highest i.e. Mount Columbia (12, 365ft – highest

point in Alberta)point in Alberta)Maximum arterial saturation < 90%; Maximum arterial saturation < 90%;

PPAAOO22<60 torr<60 torrMost common range for serious altitude Most common range for serious altitude

illnessillness

3000-5500m (10,000-18,000ft) 3000-5500m (10,000-18,000ft) i.e. Mount Columbia (12, 365ft – highest i.e. Mount Columbia (12, 365ft – highest

point in Alberta)point in Alberta)Maximum arterial saturation < 90%; Maximum arterial saturation < 90%;

PPAAOO22<60 torr<60 torrMost common range for serious altitude Most common range for serious altitude

illnessillness

Extreme AltitudeExtreme Altitude

5500-8850m (18,000-29,035ft) from Mount 5500-8850m (18,000-29,035ft) from Mount Logan (19550ft) to Mount Everest (29035ft)Logan (19550ft) to Mount Everest (29035ft)

Marked hypoxemia and hypocapniaMarked hypoxemia and hypocapnia Maximum arterial saturation 50-75%; PMaximum arterial saturation 50-75%; PAAOO22

28-40 torr28-40 torr Deterioration eventually outstrips Deterioration eventually outstrips

acclimatization, complete acclimatization not acclimatization, complete acclimatization not possiblepossible

5500-8850m (18,000-29,035ft) from Mount 5500-8850m (18,000-29,035ft) from Mount Logan (19550ft) to Mount Everest (29035ft)Logan (19550ft) to Mount Everest (29035ft)

Marked hypoxemia and hypocapniaMarked hypoxemia and hypocapnia Maximum arterial saturation 50-75%; PMaximum arterial saturation 50-75%; PAAOO22

28-40 torr28-40 torr Deterioration eventually outstrips Deterioration eventually outstrips

acclimatization, complete acclimatization not acclimatization, complete acclimatization not possiblepossible

EpidemiologyEpidemiology

Study Group # at Risk per Year

Sleeping Altitude

% AMS(# affected)

% HAPEor HACE

Western USAVisitors

40 Million 2400-2800 meters

15 (6 million) .01(4000?)

Mt. EverestTrekkers

6,000 3000-5200 meters

35 (2100) 1.0 (60?)

Mt. McKinleyClimbers

1,200 3000-5300 meters

30 (300) 2-3 (25-35)

Mt. RainierClimbers

9,000 3000 meters

67 (6000) ?

Effects of Acute Exposure to Low Atmospheric Pressures on Alveolar Gas Concentrations and Arterial Oxygen Saturation *

Arterial ArterialBarometric Po2 in Pco2 in Po2 in Oxygen Pco2 in Po2 in Oxygen Pressure Air Air Alveoli Saturation Alveoli Alveoli Saturation

Altitude (ft) (mm Hg) (mm Hg) (mm Hg) (mm Hg) (%) (mm Hg) (mm Hg) (%)

Breathing Air Breathing Pure Oxygen

0

10,000

20,000

30,000

40,000

50,000

760

523

349

226

141

87

159

110

73

47

29

18

40 (40)

36 (23)

24 (10)

24 (7)

104 (104)

67 (77)

40 (53)

18 (30)

97 (97)

90 (92)

73 (85)

24 (38)

40

40

40

40

36

24

673

436

262

139

58

16

100

100

100

99

84

15

* Numbers in parentheses are acclimatized values.. Holy Crap!!

More About Gas!More About Gas!More About Gas!More About Gas!

At sea level we are At sea level we are underneath an ocean underneath an ocean of airof air

% O% O22 is always 21% is always 21% But as you climb But as you climb

higher, the Phigher, the Patmatm drops drops and thus your POand thus your PO22 dropsdrops

At sea level we are At sea level we are underneath an ocean underneath an ocean of airof air

% O% O22 is always 21% is always 21% But as you climb But as you climb

higher, the Phigher, the Patmatm drops drops and thus your POand thus your PO22 dropsdrops

PiPiO2O2 = 0.21(P = 0.21(PBB-47)-47) PPBB=barometric pressure=barometric pressure

At sea levelAt sea level PiPiO2O2= 160 mm Hg = 160 mm Hg

At 2500mAt 2500m PiPiO2O2 = 119 mm Hg = 119 mm Hg

Aconquilcha,Chile 5340mAconquilcha,Chile 5340m PiPiO2O2 = 82 mm Hg = 82 mm Hg

On top of Everest (8848m)On top of Everest (8848m) PiPiO2O2 = 43 mm Hg = 43 mm Hg

PiPiO2O2 = 0.21(P = 0.21(PBB-47)-47) PPBB=barometric pressure=barometric pressure

At sea levelAt sea level PiPiO2O2= 160 mm Hg = 160 mm Hg

At 2500mAt 2500m PiPiO2O2 = 119 mm Hg = 119 mm Hg

Aconquilcha,Chile 5340mAconquilcha,Chile 5340m PiPiO2O2 = 82 mm Hg = 82 mm Hg

On top of Everest (8848m)On top of Everest (8848m) PiPiO2O2 = 43 mm Hg = 43 mm Hg

Thanks Rigby

Breathing pure Oxygen

Breathing air

Altitude (thousands of feet)

Art

eria

l oxy

gen

satu

ratio

n (p

er c

ent)

Figure 43-1

Breathing pure Oxygen

Breathing air

Altitude (thousands of feet)

Art

eria

l oxy

gen

satu

ratio

n (p

er c

ent)

Figure 43-1

AcclimatizationAcclimatization

Complex adaptation by essentially Complex adaptation by essentially every system to minimize hypoxia and every system to minimize hypoxia and maintain cellular functions despite maintain cellular functions despite decreased PiO2decreased PiO2

Given sufficient time most people can Given sufficient time most people can acclimatize to 5500m/18150ft, beyond acclimatize to 5500m/18150ft, beyond that progressive deterioration occursthat progressive deterioration occurs

Complex adaptation by essentially Complex adaptation by essentially every system to minimize hypoxia and every system to minimize hypoxia and maintain cellular functions despite maintain cellular functions despite decreased PiO2decreased PiO2

Given sufficient time most people can Given sufficient time most people can acclimatize to 5500m/18150ft, beyond acclimatize to 5500m/18150ft, beyond that progressive deterioration occursthat progressive deterioration occurs

So WHAT IS the problem with Altitude?So WHAT IS the problem with Altitude?

HYPOXIAHYPOXIA

WHAT ARE THE PHYSIOLOGIC WHAT ARE THE PHYSIOLOGIC COMPENSATIONS?COMPENSATIONS? Essentially all the physiologic changes are Essentially all the physiologic changes are

attempting to improve arterial and therefore attempting to improve arterial and therefore cellular oxygenationcellular oxygenation

HYPOXIAHYPOXIA

WHAT ARE THE PHYSIOLOGIC WHAT ARE THE PHYSIOLOGIC COMPENSATIONS?COMPENSATIONS? Essentially all the physiologic changes are Essentially all the physiologic changes are

attempting to improve arterial and therefore attempting to improve arterial and therefore cellular oxygenationcellular oxygenation

Pulmonary Response to PiO2Pulmonary Response to PiO2

Hypoxemic Ventilatory ResponseHypoxemic Ventilatory Response Begins w/i minutes of ascent above 1500mBegins w/i minutes of ascent above 1500m

Hypoxia - pulmonary vasoconstrictorHypoxia - pulmonary vasoconstrictor Allows for selective shunting away from areas of Allows for selective shunting away from areas of

hypoxia w/preferential areas of hypoxia w/preferential areas of vasodilationvasodilation

pulmonary vascular resistancepulmonary vascular resistance pulmonary artery pressure (cold and exercise PAP pulmonary artery pressure (cold and exercise PAP

while descent, O2 and certain Rx PAP)while descent, O2 and certain Rx PAP)

diffusion capacity and lung volumediffusion capacity and lung volume

Hypoxemic Ventilatory ResponseHypoxemic Ventilatory Response Begins w/i minutes of ascent above 1500mBegins w/i minutes of ascent above 1500m

Hypoxia - pulmonary vasoconstrictorHypoxia - pulmonary vasoconstrictor Allows for selective shunting away from areas of Allows for selective shunting away from areas of

hypoxia w/preferential areas of hypoxia w/preferential areas of vasodilationvasodilation

pulmonary vascular resistancepulmonary vascular resistance pulmonary artery pressure (cold and exercise PAP pulmonary artery pressure (cold and exercise PAP

while descent, O2 and certain Rx PAP)while descent, O2 and certain Rx PAP)

diffusion capacity and lung volumediffusion capacity and lung volume

Hypoxemic Ventilatory ResponseHypoxemic Ventilatory Response

Ventilation increases proportionally to the Ventilation increases proportionally to the degree of hypoxia detected at the degree of hypoxia detected at the chemoreceptors chemoreceptors Lower PaCO2 = higher PLower PaCO2 = higher PAAO2O2 remember … Premember … PAAO2 = PiO2 - PaCO2/RO2 = PiO2 - PaCO2/R As PCO2 drops a respiratory alkalosis occurs (what As PCO2 drops a respiratory alkalosis occurs (what

does this do to the medulla?) does this do to the medulla?) kidneys compensate by excreting bicarb(over 6-8/7)kidneys compensate by excreting bicarb(over 6-8/7)

Vigourous HVR helps acclimatization Vigourous HVR helps acclimatization whereas a poor HVR may lead to altitude-whereas a poor HVR may lead to altitude-illnessillness

Ventilation increases proportionally to the Ventilation increases proportionally to the degree of hypoxia detected at the degree of hypoxia detected at the chemoreceptors chemoreceptors Lower PaCO2 = higher PLower PaCO2 = higher PAAO2O2 remember … Premember … PAAO2 = PiO2 - PaCO2/RO2 = PiO2 - PaCO2/R As PCO2 drops a respiratory alkalosis occurs (what As PCO2 drops a respiratory alkalosis occurs (what

does this do to the medulla?) does this do to the medulla?) kidneys compensate by excreting bicarb(over 6-8/7)kidneys compensate by excreting bicarb(over 6-8/7)

Vigourous HVR helps acclimatization Vigourous HVR helps acclimatization whereas a poor HVR may lead to altitude-whereas a poor HVR may lead to altitude-illnessillness

HVRHVR

Carotid bodies O2

Aortic bodies

Cerebral CirculationCerebral Circulation

Hypoxemia = increases cerebral blood flowHypoxemia = increases cerebral blood flow Hypocapnea = decreases cerebral blood flowHypocapnea = decreases cerebral blood flow Net result is an increase (modest) in cerebral Net result is an increase (modest) in cerebral

blood flow at PaO2 <60 (altitude >12,500 blood flow at PaO2 <60 (altitude >12,500 feet)feet) Contributes to pathophysiology of AMS and HACEContributes to pathophysiology of AMS and HACE

Hypoxemia = increases cerebral blood flowHypoxemia = increases cerebral blood flow Hypocapnea = decreases cerebral blood flowHypocapnea = decreases cerebral blood flow Net result is an increase (modest) in cerebral Net result is an increase (modest) in cerebral

blood flow at PaO2 <60 (altitude >12,500 blood flow at PaO2 <60 (altitude >12,500 feet)feet) Contributes to pathophysiology of AMS and HACEContributes to pathophysiology of AMS and HACE

CVS ResponseCVS Response

Catecholamine release: Epi and NorepiCatecholamine release: Epi and Norepi Sympathetic Tone: Sympathetic Tone: CO= HR x SVCO= HR x SV BP= CO x PVRBP= CO x PVR

This responses allows for better tissue This responses allows for better tissue perfusion (but, also decreases exercise perfusion (but, also decreases exercise performance) – over time epi/norepi performance) – over time epi/norepi levels drop and CO/HR/PVR return to levels drop and CO/HR/PVR return to normalnormal

Catecholamine release: Epi and NorepiCatecholamine release: Epi and Norepi Sympathetic Tone: Sympathetic Tone: CO= HR x SVCO= HR x SV BP= CO x PVRBP= CO x PVR

This responses allows for better tissue This responses allows for better tissue perfusion (but, also decreases exercise perfusion (but, also decreases exercise performance) – over time epi/norepi performance) – over time epi/norepi levels drop and CO/HR/PVR return to levels drop and CO/HR/PVR return to normalnormal

HematologicHematologic

Blood volume increases immediately: Blood volume increases immediately: Primarily due to hemo[ ] from diuresisPrimarily due to hemo[ ] from diuresis

Hypoxia stimulates renal EPO productionHypoxia stimulates renal EPO production Takes weeks for it to effect Red Cell MassTakes weeks for it to effect Red Cell Mass

Oxygen Dissociation curve – combination of Oxygen Dissociation curve – combination of inc 2,3 DPG (rightward shift) and alkalosis inc 2,3 DPG (rightward shift) and alkalosis (leftward shift) leads to minimal net effect(leftward shift) leads to minimal net effect

Blood volume increases immediately: Blood volume increases immediately: Primarily due to hemo[ ] from diuresisPrimarily due to hemo[ ] from diuresis

Hypoxia stimulates renal EPO productionHypoxia stimulates renal EPO production Takes weeks for it to effect Red Cell MassTakes weeks for it to effect Red Cell Mass

Oxygen Dissociation curve – combination of Oxygen Dissociation curve – combination of inc 2,3 DPG (rightward shift) and alkalosis inc 2,3 DPG (rightward shift) and alkalosis (leftward shift) leads to minimal net effect(leftward shift) leads to minimal net effect

AcclimatizationAcclimatizationAcute Chronic

Ventilation, O2 Diffusion capacity

Ventilation

Heart Rate Red Cell Mass (from EPO release)

Cerebral Blood Flow Metabolism (tissue changes)

Diuresis, Hct (from volume contraction)

Gotta know it. It’ll be on the exam!

High Altitude IllnessHigh Altitude Illness

What are RF?What are RF?What are positive predictors?What are positive predictors?What worsens altitude illnesses?What worsens altitude illnesses?What does not effect altitude illnesses?What does not effect altitude illnesses?

What are RF?What are RF?What are positive predictors?What are positive predictors?What worsens altitude illnesses?What worsens altitude illnesses?What does not effect altitude illnesses?What does not effect altitude illnesses?

High Altitude IllnessHigh Altitude Illness What are Risk Factors?What are Risk Factors?

Rate of ascent/Starting altitudeRate of ascent/Starting altitude Altitude reachedAltitude reached Sleeping at altitudeSleeping at altitude Individual physiology/Genetics?Individual physiology/Genetics?

What are Positive Predictors?What are Positive Predictors? Hx of prior ascent w/o SxHx of prior ascent w/o Sx Elderly (less AMS/HACE), Women (less HAPE)Elderly (less AMS/HACE), Women (less HAPE)

What are Risk Factors?What are Risk Factors? Rate of ascent/Starting altitudeRate of ascent/Starting altitude Altitude reachedAltitude reached Sleeping at altitudeSleeping at altitude Individual physiology/Genetics?Individual physiology/Genetics?

What are Positive Predictors?What are Positive Predictors? Hx of prior ascent w/o SxHx of prior ascent w/o Sx Elderly (less AMS/HACE), Women (less HAPE)Elderly (less AMS/HACE), Women (less HAPE)

What worsens altitude-illnesses?What worsens altitude-illnesses? Respiratory depressants/AlcoholRespiratory depressants/Alcohol Pre-existing Medical Illnesses (very few): Pre-existing Medical Illnesses (very few):

i.e. Pulm HTN, certain CHD, i.e. Pulm HTN, certain CHD, ExertionExertion HypothermiaHypothermia

What does not affect risk?What does not affect risk? Physical fitnessPhysical fitness CAD/HTNCAD/HTN Mild COPDMild COPD PregnancyPregnancy DMDM

What worsens altitude-illnesses?What worsens altitude-illnesses? Respiratory depressants/AlcoholRespiratory depressants/Alcohol Pre-existing Medical Illnesses (very few): Pre-existing Medical Illnesses (very few):

i.e. Pulm HTN, certain CHD, i.e. Pulm HTN, certain CHD, ExertionExertion HypothermiaHypothermia

What does not affect risk?What does not affect risk? Physical fitnessPhysical fitness CAD/HTNCAD/HTN Mild COPDMild COPD PregnancyPregnancy DMDM

Case #1Case #1

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

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

What’s your Diagnosis?What’s your Diagnosis?

1.1. Acute Mountain SyndromeAcute Mountain Syndrome2.2. High Altitude Cerebral EdemaHigh Altitude Cerebral Edema3.3. High Altitude Pulmonary EdemaHigh Altitude Pulmonary Edema4.4. Other Medical IllnessOther Medical Illness

1.1. Acute Mountain SyndromeAcute Mountain Syndrome2.2. High Altitude Cerebral EdemaHigh Altitude Cerebral Edema3.3. High Altitude Pulmonary EdemaHigh Altitude Pulmonary Edema4.4. Other Medical IllnessOther Medical Illness

PearlPearl

Any illness at altitude is altitude Any illness at altitude is altitude illness until proven otherwise.illness until proven otherwise.

Any illness at altitude is altitude Any illness at altitude is altitude illness until proven otherwise.illness until proven otherwise.

Lake Louise Criteria for AMSLake Louise Criteria for AMS

Presence of a Presence of a HAHA in an un-acclimatized in an un-acclimatized person who has arrived at an altitude person who has arrived at an altitude >2000m (usu >2500m)>2000m (usu >2500m) + 1 of + 1 of GI (anorexia, N,V)GI (anorexia, N,V) FatigueFatigue InsomniaInsomnia Dizziness/lightheadedDizziness/lightheaded

Sx usually begin between 6-10 hrs but Sx usually begin between 6-10 hrs but may be as early as 1 hourmay be as early as 1 hour

Presence of a Presence of a HAHA in an un-acclimatized in an un-acclimatized person who has arrived at an altitude person who has arrived at an altitude >2000m (usu >2500m)>2000m (usu >2500m) + 1 of + 1 of GI (anorexia, N,V)GI (anorexia, N,V) FatigueFatigue InsomniaInsomnia Dizziness/lightheadedDizziness/lightheaded

Sx usually begin between 6-10 hrs but Sx usually begin between 6-10 hrs but may be as early as 1 hourmay be as early as 1 hour

PearlsPearls

Never ascend with symptoms Never ascend with symptoms of AMSof AMS

Never leave someone with AMS Never leave someone with AMS alonealone

-Letting someone with AMS hike alone is the equilavent -Letting someone with AMS hike alone is the equilavent of going for a hike in the Kananaski’s alone the of going for a hike in the Kananaski’s alone the

night of night of Party at the retreat.Party at the retreat.

Never ascend with symptoms Never ascend with symptoms of AMSof AMS

Never leave someone with AMS Never leave someone with AMS alonealone

-Letting someone with AMS hike alone is the equilavent -Letting someone with AMS hike alone is the equilavent of going for a hike in the Kananaski’s alone the of going for a hike in the Kananaski’s alone the

night of night of Party at the retreat.Party at the retreat.

AMS PathophysiologyAMS Pathophysiology

Altitude Hypoxia

CBF Blood-brain barrierpermeability Na+K+ATPase

ICFCBV Vasogenic edema

Mild brain swelling

CSF volumebuffering

Adequate Inadequate

AMSNo AMS

Treatment?Treatment?

Any or CombinationAny or Combination Stop, Rest and Continue once Sx resolveStop, Rest and Continue once Sx resolve Acetazolimide (alone or in combination)Acetazolimide (alone or in combination) DexamethasoneDexamethasone O2, immediate descentO2, immediate descent NifedipineNifedipine + Symptomatic Treatment+ Symptomatic Treatment

Any or CombinationAny or Combination Stop, Rest and Continue once Sx resolveStop, Rest and Continue once Sx resolve Acetazolimide (alone or in combination)Acetazolimide (alone or in combination) DexamethasoneDexamethasone O2, immediate descentO2, immediate descent NifedipineNifedipine + Symptomatic Treatment+ Symptomatic Treatment

Treatment?Treatment?

Any or CombinationAny or Combination1.1. Stop, Rest and Continue once Sx resolveStop, Rest and Continue once Sx resolve2.2. Acetazolamide (alone or in combination)Acetazolamide (alone or in combination)3.3. Dexamethasone (if severe)Dexamethasone (if severe)4.4. O2, rapid/immediate descentO2, rapid/immediate descent5.5. NifedipineNifedipine6.6. + Symptomatic Treatment+ Symptomatic Treatment

Any or CombinationAny or Combination1.1. Stop, Rest and Continue once Sx resolveStop, Rest and Continue once Sx resolve2.2. Acetazolamide (alone or in combination)Acetazolamide (alone or in combination)3.3. Dexamethasone (if severe)Dexamethasone (if severe)4.4. O2, rapid/immediate descentO2, rapid/immediate descent5.5. NifedipineNifedipine6.6. + Symptomatic Treatment+ Symptomatic Treatment

Treatment Options of AMSTreatment Options of AMS

Stop and rest at altitude that Sx 1Stop and rest at altitude that Sx 1stst develop +/- Acetazolamide -> May develop +/- Acetazolamide -> May proceed once Sx abateproceed once Sx abate

+ Tx Sx+ Tx Sx Nausea: Prochlorperazine 10mg po/im Nausea: Prochlorperazine 10mg po/im

(stimulates HVR)(stimulates HVR) HA: Tylenol/NSAID’sHA: Tylenol/NSAID’s Insomnia: acetazolamide 125mg PO QHSInsomnia: acetazolamide 125mg PO QHS

Stop and rest at altitude that Sx 1Stop and rest at altitude that Sx 1stst develop +/- Acetazolamide -> May develop +/- Acetazolamide -> May proceed once Sx abateproceed once Sx abate

+ Tx Sx+ Tx Sx Nausea: Prochlorperazine 10mg po/im Nausea: Prochlorperazine 10mg po/im

(stimulates HVR)(stimulates HVR) HA: Tylenol/NSAID’sHA: Tylenol/NSAID’s Insomnia: acetazolamide 125mg PO QHSInsomnia: acetazolamide 125mg PO QHS

Treatment of AMSTreatment of AMSTreatment of AMSTreatment of AMS Mild SymptomsMild Symptoms Does not need descent Does not need descent

if mild Sx and constant if mild Sx and constant supervisionsupervision

Stop ascent until betterStop ascent until better Acetazolamide (250 Acetazolamide (250

BID)BID) Tylenol/ASA for SxTylenol/ASA for Sx Anti-emetic PRNAnti-emetic PRN Consider OConsider O22 at 1-2 at 1-2

LPMLPM

Mild SymptomsMild Symptoms Does not need descent Does not need descent

if mild Sx and constant if mild Sx and constant supervisionsupervision

Stop ascent until betterStop ascent until better Acetazolamide (250 Acetazolamide (250

BID)BID) Tylenol/ASA for SxTylenol/ASA for Sx Anti-emetic PRNAnti-emetic PRN Consider OConsider O22 at 1-2 at 1-2

LPMLPM

Moderate or Moderate or Unresolving AMSUnresolving AMS

Descent 500 mDescent 500 m Consider:Consider:

OO22 at 1-2 LPM at 1-2 LPM Hyperbaric therapyHyperbaric therapy Dexamethasone Dexamethasone

4mg PO q6h until 4mg PO q6h until able to descendable to descend

May ascend after May ascend after symptoms resolvesymptoms resolve

Moderate or Moderate or Unresolving AMSUnresolving AMS

Descent 500 mDescent 500 m Consider:Consider:

OO22 at 1-2 LPM at 1-2 LPM Hyperbaric therapyHyperbaric therapy Dexamethasone Dexamethasone

4mg PO q6h until 4mg PO q6h until able to descendable to descend

May ascend after May ascend after symptoms resolvesymptoms resolve

If If someone is someone is getting worse, go down getting worse, go down at onceat once

If Sx of HACE are present DESCEND If Sx of HACE are present DESCEND IMMEDIATELYIMMEDIATELY

If If someone is someone is getting worse, go down getting worse, go down at onceat once

If Sx of HACE are present DESCEND If Sx of HACE are present DESCEND IMMEDIATELYIMMEDIATELY

Quick word about AcetazolamideQuick word about Acetazolamide

What’s the MOA?What’s the MOA?What’s the MOA?What’s the MOA?

Quick word about AcetazolamideQuick word about Acetazolamide

What’s the MOA?What’s the MOA? Causes a bicarb diuresis by inhibiting Causes a bicarb diuresis by inhibiting

Carbonic Anhydrase at the kidney Carbonic Anhydrase at the kidney This leads to a metabolic acidosis which This leads to a metabolic acidosis which

counteracts the alkalosis from counteracts the alkalosis from hyperventilationhyperventilation

Allowing an individual to have a better HVR Allowing an individual to have a better HVR and therefore acclimatize betterand therefore acclimatize better

Which allergy must you ask about?Which allergy must you ask about?

What’s the MOA?What’s the MOA? Causes a bicarb diuresis by inhibiting Causes a bicarb diuresis by inhibiting

Carbonic Anhydrase at the kidney Carbonic Anhydrase at the kidney This leads to a metabolic acidosis which This leads to a metabolic acidosis which

counteracts the alkalosis from counteracts the alkalosis from hyperventilationhyperventilation

Allowing an individual to have a better HVR Allowing an individual to have a better HVR and therefore acclimatize betterand therefore acclimatize better

Which allergy must you ask about?Which allergy must you ask about?

Pt adamant that the HA is from Pt adamant that the HA is from dehydrationdehydration Can give Dx/Tx of 1L of fluid + advil or Can give Dx/Tx of 1L of fluid + advil or

tylenol – if this completely resolves HA, not tylenol – if this completely resolves HA, not likely to be AMSlikely to be AMS

Pt adamant that the HA is from Pt adamant that the HA is from dehydrationdehydration Can give Dx/Tx of 1L of fluid + advil or Can give Dx/Tx of 1L of fluid + advil or

tylenol – if this completely resolves HA, not tylenol – if this completely resolves HA, not likely to be AMSlikely to be AMS

Case #2Case #2

Despite the advice to refrain from Despite the advice to refrain from continuing to ascend, you continue up continuing to ascend, you continue up and begin to feel disoriented and and begin to feel disoriented and noticed you seem to be walking with a noticed you seem to be walking with a drunken’ sort of gaitdrunken’ sort of gait

Dx?Dx?

Despite the advice to refrain from Despite the advice to refrain from continuing to ascend, you continue up continuing to ascend, you continue up and begin to feel disoriented and and begin to feel disoriented and noticed you seem to be walking with a noticed you seem to be walking with a drunken’ sort of gaitdrunken’ sort of gait

Dx?Dx?

High Altitude Cerebral Edema (HACE)High Altitude Cerebral Edema (HACE)

Least common but most lethal altitude illnessLeast common but most lethal altitude illness Usually occurs above 3600m(12,000 feet)Usually occurs above 3600m(12,000 feet) Symptoms usually develop over 1-3 daysSymptoms usually develop over 1-3 days

reported range 12 hours to 9 daysreported range 12 hours to 9 days Usually also have symptoms of AMS / HAPEUsually also have symptoms of AMS / HAPE

Least common but most lethal altitude illnessLeast common but most lethal altitude illness Usually occurs above 3600m(12,000 feet)Usually occurs above 3600m(12,000 feet) Symptoms usually develop over 1-3 daysSymptoms usually develop over 1-3 days

reported range 12 hours to 9 daysreported range 12 hours to 9 days Usually also have symptoms of AMS / HAPEUsually also have symptoms of AMS / HAPE

HACE DxHACE Dx

• Presence of a change in mental status and/or Presence of a change in mental status and/or ataxia in a person with AMSataxia in a person with AMS

OrOr

• Presence of both mental status changes and Presence of both mental status changes and ataxia in a person without AMSataxia in a person without AMS

• Presence of a change in mental status and/or Presence of a change in mental status and/or ataxia in a person with AMSataxia in a person with AMS

OrOr

• Presence of both mental status changes and Presence of both mental status changes and ataxia in a person without AMSataxia in a person without AMS

HACE S & SxHACE S & Sx

Think of the effect of hypoxia and ICPThink of the effect of hypoxia and ICP Global encephalopathyGlobal encephalopathy AtaxiaAtaxia Altered mentationAltered mentation SeizuresSeizures Occasional CN palsies (secondary to increased Occasional CN palsies (secondary to increased

ICP)ICP) PapilledemaPapilledema Retinal hemorrhageRetinal hemorrhage ComaComa Death is due to brain herniationDeath is due to brain herniation

Think of the effect of hypoxia and ICPThink of the effect of hypoxia and ICP Global encephalopathyGlobal encephalopathy AtaxiaAtaxia Altered mentationAltered mentation SeizuresSeizures Occasional CN palsies (secondary to increased Occasional CN palsies (secondary to increased

ICP)ICP) PapilledemaPapilledema Retinal hemorrhageRetinal hemorrhage ComaComa Death is due to brain herniationDeath is due to brain herniation

HACE PathophysHACE Pathophys

Altitude Hypoxia

CBF Blood-brain barrierpermeabilityNa+K+ATPase

ICFCBV Vasogenic edema

Mild brain swelling

CSF volumebuffering

Adequate Inadequate

AMSNo AMS

Severe hypoxemia

Fluid retention

HACE

Management?Management?Management?Management?

Tx of HACETx of HACE

DESCENT (until pt improves)DESCENT (until pt improves)O2O2DXM 8mg PO/IM/IV initially then 4mg DXM 8mg PO/IM/IV initially then 4mg

Q6HQ6H+/- acetazolamide 250mg PO BID +/- acetazolamide 250mg PO BID What if the weather does not allow for a What if the weather does not allow for a

safe descent and you happen to be part safe descent and you happen to be part of a well equipped expedition?of a well equipped expedition?

DESCENT (until pt improves)DESCENT (until pt improves)O2O2DXM 8mg PO/IM/IV initially then 4mg DXM 8mg PO/IM/IV initially then 4mg

Q6HQ6H+/- acetazolamide 250mg PO BID +/- acetazolamide 250mg PO BID What if the weather does not allow for a What if the weather does not allow for a

safe descent and you happen to be part safe descent and you happen to be part of a well equipped expedition?of a well equipped expedition?

Protective Inflatable Toboggan?Protective Inflatable Toboggan?

Gamow BagGamow Bag

Hyperbaric ChambersHyperbaric Chambers Lightweight (14.9 lb)Lightweight (14.9 lb) Manually pressurizedManually pressurized Generate 103mm Hg (2 psi) above ambient Generate 103mm Hg (2 psi) above ambient

pressurepressure Simulates descent of 4000-5000 feet at moderate Simulates descent of 4000-5000 feet at moderate

altitudesaltitudes Simulates descent of 9000 feet at top of Mt. EverestSimulates descent of 9000 feet at top of Mt. Everest

After short course of treatment patient often able After short course of treatment patient often able to descend on their own to descend on their own

This is primarily a temporizing measure - This is primarily a temporizing measure - Not an Not an alternate to descendingalternate to descending

Hyperbaric ChambersHyperbaric Chambers Lightweight (14.9 lb)Lightweight (14.9 lb) Manually pressurizedManually pressurized Generate 103mm Hg (2 psi) above ambient Generate 103mm Hg (2 psi) above ambient

pressurepressure Simulates descent of 4000-5000 feet at moderate Simulates descent of 4000-5000 feet at moderate

altitudesaltitudes Simulates descent of 9000 feet at top of Mt. EverestSimulates descent of 9000 feet at top of Mt. Everest

After short course of treatment patient often able After short course of treatment patient often able to descend on their own to descend on their own

This is primarily a temporizing measure - This is primarily a temporizing measure - Not an Not an alternate to descendingalternate to descending

Case #3Case #3

During a visit to Nepal, Mr. Hackalung, During a visit to Nepal, Mr. Hackalung, decides to organize a hike to Everest decides to organize a hike to Everest Base camp (5430m/18000ft).Base camp (5430m/18000ft).

On day 3 you notice you notice he On day 3 you notice you notice he develops a dry cough and during the develops a dry cough and during the lunch break he’s quite SOBlunch break he’s quite SOB

You’re the group docYou’re the group doc What’s the most likely Dx?What’s the most likely Dx?

During a visit to Nepal, Mr. Hackalung, During a visit to Nepal, Mr. Hackalung, decides to organize a hike to Everest decides to organize a hike to Everest Base camp (5430m/18000ft).Base camp (5430m/18000ft).

On day 3 you notice you notice he On day 3 you notice you notice he develops a dry cough and during the develops a dry cough and during the lunch break he’s quite SOBlunch break he’s quite SOB

You’re the group docYou’re the group doc What’s the most likely Dx?What’s the most likely Dx?

Case #3Case #3

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

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

Responsible for most high altitude deathsResponsible for most high altitude deathsRelatively Abrupt OnsetRelatively Abrupt OnsetUsually occurs on 2Usually occurs on 2ndnd night at altitude, Rare night at altitude, Rare

after 4 daysafter 4 daysWomen less susceptible than menWomen less susceptible than menPresence of HAPE increases likelihood of Presence of HAPE increases likelihood of

cerebral illnesses – by worsening hypoxemia: cerebral illnesses – by worsening hypoxemia: 50% have AMS & 14% have HACE50% have AMS & 14% have HACE

Responsible for most high altitude deathsResponsible for most high altitude deathsRelatively Abrupt OnsetRelatively Abrupt OnsetUsually occurs on 2Usually occurs on 2ndnd night at altitude, Rare night at altitude, Rare

after 4 daysafter 4 daysWomen less susceptible than menWomen less susceptible than menPresence of HAPE increases likelihood of Presence of HAPE increases likelihood of

cerebral illnesses – by worsening hypoxemia: cerebral illnesses – by worsening hypoxemia: 50% have AMS & 14% have HACE50% have AMS & 14% have HACE

High Altitude Pulmonary Edema (HAPE)

HAPE DiagnosisHAPE Diagnosis

At least two of the At least two of the following Sx:following Sx: Dyspnea at restDyspnea at rest CoughCough Weakness or Weakness or

decreased exercise decreased exercise performanceperformance

Chest tightness or Chest tightness or congestioncongestion

At least two of the At least two of the following Sx:following Sx: Dyspnea at restDyspnea at rest CoughCough Weakness or Weakness or

decreased exercise decreased exercise performanceperformance

Chest tightness or Chest tightness or congestioncongestion

At least two of the At least two of the following signs:following signs: Central cyanosisCentral cyanosis Audible crackles or Audible crackles or

wheezing in at least wheezing in at least one lung fieldone lung field

TachypneaTachypnea tachycardiatachycardia

At least two of the At least two of the following signs:following signs: Central cyanosisCentral cyanosis Audible crackles or Audible crackles or

wheezing in at least wheezing in at least one lung fieldone lung field

TachypneaTachypnea tachycardiatachycardia

HAPE PathophysHAPE PathophysPAO2

Platelet and FibrinMicroemboli

SympatheticDischarge

Hypoxic PulmonaryVasoconstriction

Central NervousSystem

VascularObstruction

Pulmonary Blood Volume

PulmonaryHypertension

Pulmonary VenousConstriction?

Local Overperfusion

Failure of Capillary Membrane

Permeability Leak

HAPE

Increase CWP & PAP

Doc, how do you want to treat him?Doc, how do you want to treat him? You have access to most drugs, but no You have access to most drugs, but no

monitoring equipment.monitoring equipment.

Doc, how do you want to treat him?Doc, how do you want to treat him? You have access to most drugs, but no You have access to most drugs, but no

monitoring equipment.monitoring equipment.

HAPE Tx – Increase PiO2HAPE Tx – Increase PiO2

Definitive TxDefinitive Tx Descent or Simulated Descent or Simulated

descent (if unable to descent (if unable to Descend)Descend)

Supplemental O2 Supplemental O2 (SaO2>90%)(SaO2>90%)

May be a role for observant May be a role for observant management (bed rest/O2) if mild management (bed rest/O2) if mild case and experienced and well-case and experienced and well-equipped physician presentequipped physician present

Definitive TxDefinitive Tx Descent or Simulated Descent or Simulated

descent (if unable to descent (if unable to Descend)Descend)

Supplemental O2 Supplemental O2 (SaO2>90%)(SaO2>90%)

May be a role for observant May be a role for observant management (bed rest/O2) if mild management (bed rest/O2) if mild case and experienced and well-case and experienced and well-equipped physician presentequipped physician present

Temporizing Temporizing MeasuresMeasures

Nifedipine 10mg PONifedipine 10mg PO Ventolin Ventolin DiamoxDiamox PEEPPEEP Viagra – currently Viagra – currently

being studiedbeing studied DXM – no benefitDXM – no benefit

Temporizing Temporizing MeasuresMeasures

Nifedipine 10mg PONifedipine 10mg PO Ventolin Ventolin DiamoxDiamox PEEPPEEP Viagra – currently Viagra – currently

being studiedbeing studied DXM – no benefitDXM – no benefit

PreventionPrevention

Rational Ascent (MOST IMPORTANT)Rational Ascent (MOST IMPORTANT) First night not higher than 2400m (8000 feet)First night not higher than 2400m (8000 feet) CLIMB HIGH, SLEEP LOW. CLIMB HIGH, SLEEP LOW. At altitudes above At altitudes above

3000 meters (10,000 feet), your sleeping elevation 3000 meters (10,000 feet), your sleeping elevation should not increase more than 300 meters (1000 should not increase more than 300 meters (1000 feet) per night,feet) per night, daytime increase of 600m. daytime increase of 600m.

EEvery 1000 meters (3very 1000 meters (33300 feet)00 feet) of sleeping of sleeping elevation gainelevation gain you should spend a second night. you should spend a second night.

Ginko bilobaGinko biloba   Limited studies have been performed, but the Limited studies have been performed, but the

results look very promising for prophylaxis of AMS. results look very promising for prophylaxis of AMS. 120 mg po BID starting 5 days before ascent, and 120 mg po BID starting 5 days before ascent, and continuing at altitude.continuing at altitude.

Rational Ascent (MOST IMPORTANT)Rational Ascent (MOST IMPORTANT) First night not higher than 2400m (8000 feet)First night not higher than 2400m (8000 feet) CLIMB HIGH, SLEEP LOW. CLIMB HIGH, SLEEP LOW. At altitudes above At altitudes above

3000 meters (10,000 feet), your sleeping elevation 3000 meters (10,000 feet), your sleeping elevation should not increase more than 300 meters (1000 should not increase more than 300 meters (1000 feet) per night,feet) per night, daytime increase of 600m. daytime increase of 600m.

EEvery 1000 meters (3very 1000 meters (33300 feet)00 feet) of sleeping of sleeping elevation gainelevation gain you should spend a second night. you should spend a second night.

Ginko bilobaGinko biloba   Limited studies have been performed, but the Limited studies have been performed, but the

results look very promising for prophylaxis of AMS. results look very promising for prophylaxis of AMS. 120 mg po BID starting 5 days before ascent, and 120 mg po BID starting 5 days before ascent, and continuing at altitude.continuing at altitude.

AcetazolamideAcetazolamide Not routinely indicated but use consider Not routinely indicated but use consider

if; if; Forced rapid ascent (1 day) to altitudes Forced rapid ascent (1 day) to altitudes

over 3000mover 3000m.. A rapid gain in sleeping elevation - for A rapid gain in sleeping elevation - for

example gaining 1000 m in one day. example gaining 1000 m in one day. A history of recurrent AMS.A history of recurrent AMS.

Dose: 125 mg BID, 24 hrs before ascent Dose: 125 mg BID, 24 hrs before ascent + 2-3/7 after ascent+ 2-3/7 after ascent

AcetazolamideAcetazolamide Not routinely indicated but use consider Not routinely indicated but use consider

if; if; Forced rapid ascent (1 day) to altitudes Forced rapid ascent (1 day) to altitudes

over 3000mover 3000m.. A rapid gain in sleeping elevation - for A rapid gain in sleeping elevation - for

example gaining 1000 m in one day. example gaining 1000 m in one day. A history of recurrent AMS.A history of recurrent AMS.

Dose: 125 mg BID, 24 hrs before ascent Dose: 125 mg BID, 24 hrs before ascent + 2-3/7 after ascent+ 2-3/7 after ascent

DXMDXM Indication – Hx of AMS, but diamox Indication – Hx of AMS, but diamox

probably preferredprobably preferred Dose: 2mg PO Q6H, start day before Dose: 2mg PO Q6H, start day before

ascent and continue until at max altitude x ascent and continue until at max altitude x 48 hrs48 hrs

Nifedipine ERNifedipine ER Indication – Hx of HAPEIndication – Hx of HAPE 20-30mg PO BID, start day before ascent 20-30mg PO BID, start day before ascent

and continue until at max altitude x 48 hrsand continue until at max altitude x 48 hrs

DXMDXM Indication – Hx of AMS, but diamox Indication – Hx of AMS, but diamox

probably preferredprobably preferred Dose: 2mg PO Q6H, start day before Dose: 2mg PO Q6H, start day before

ascent and continue until at max altitude x ascent and continue until at max altitude x 48 hrs48 hrs

Nifedipine ERNifedipine ER Indication – Hx of HAPEIndication – Hx of HAPE 20-30mg PO BID, start day before ascent 20-30mg PO BID, start day before ascent

and continue until at max altitude x 48 hrsand continue until at max altitude x 48 hrs

AvoidAvoid AlcoholAlcohol Sleeping Pills (diamox is the Rx of choice)Sleeping Pills (diamox is the Rx of choice) Narcotics (other than at moderate doses)Narcotics (other than at moderate doses)

Avoid overexertionAvoid overexertionStay warmStay warm

AvoidAvoid AlcoholAlcohol Sleeping Pills (diamox is the Rx of choice)Sleeping Pills (diamox is the Rx of choice) Narcotics (other than at moderate doses)Narcotics (other than at moderate doses)

Avoid overexertionAvoid overexertionStay warmStay warm

PearlsPearls

SUMMARY: DESCEND IF UNSURE SUMMARY: DESCEND IF UNSURE All other Tx are only temporizing for life-All other Tx are only temporizing for life-

threatening illnessesthreatening illnesses

SUMMARY: DESCEND IF UNSURE SUMMARY: DESCEND IF UNSURE All other Tx are only temporizing for life-All other Tx are only temporizing for life-

threatening illnessesthreatening illnesses

What Should make you think of Other diagnoses?What Should make you think of Other diagnoses?

Onset of Sx >3/7 after ascent to a given Onset of Sx >3/7 after ascent to a given altitudealtitude

Lack of a HALack of a HARapid response to rest/stopping ascentRapid response to rest/stopping ascentLack of response to descent, O2, or Lack of response to descent, O2, or

dexamethasone(unless HAPE)dexamethasone(unless HAPE)

Onset of Sx >3/7 after ascent to a given Onset of Sx >3/7 after ascent to a given altitudealtitude

Lack of a HALack of a HARapid response to rest/stopping ascentRapid response to rest/stopping ascentLack of response to descent, O2, or Lack of response to descent, O2, or

dexamethasone(unless HAPE)dexamethasone(unless HAPE)

SummarySummary

Early recognition is importantEarly recognition is importantAMSAMS

stop ascent, rest, +/- diamox, Tx Sxstop ascent, rest, +/- diamox, Tx SxHACEHACE

DESCENT +/- DXM, diamoxDESCENT +/- DXM, diamoxHAPEHAPE

DESCENT +/- nifedipine, ventolinDESCENT +/- nifedipine, ventolin

Early recognition is importantEarly recognition is importantAMSAMS

stop ascent, rest, +/- diamox, Tx Sxstop ascent, rest, +/- diamox, Tx SxHACEHACE

DESCENT +/- DXM, diamoxDESCENT +/- DXM, diamoxHAPEHAPE

DESCENT +/- nifedipine, ventolinDESCENT +/- nifedipine, ventolin

ReferencesReferences

High-Altitude Illness. Emerg M Clinics of N High-Altitude Illness. Emerg M Clinics of N America, 2004.America, 2004.

High-Altitude Illness. NEJM, July 2001.High-Altitude Illness. NEJM, July 2001. Rosen’s.Rosen’s. Guyton. Textbook of Medical PhysiologyGuyton. Textbook of Medical Physiology Aric’s Rounds 2003Aric’s Rounds 2003 Rigby’s NRC lectureRigby’s NRC lecture

High-Altitude Illness. Emerg M Clinics of N High-Altitude Illness. Emerg M Clinics of N America, 2004.America, 2004.

High-Altitude Illness. NEJM, July 2001.High-Altitude Illness. NEJM, July 2001. Rosen’s.Rosen’s. Guyton. Textbook of Medical PhysiologyGuyton. Textbook of Medical Physiology Aric’s Rounds 2003Aric’s Rounds 2003 Rigby’s NRC lectureRigby’s NRC lecture

So what’s UP with Altitude?So what’s UP with Altitude?

Barometric pressure decreases as Barometric pressure decreases as altitude rises (hypobaria) and with altitude rises (hypobaria) and with higher latitudeshigher latitudes

Hypobaria decreases the partial Hypobaria decreases the partial pressure of O2: 0.021 x Atm Pressure pressure of O2: 0.021 x Atm Pressure = PiO2, note- [02] remains at 21%= PiO2, note- [02] remains at 21%

Changes in weather (eg: low pressure Changes in weather (eg: low pressure front) can change relative altitude (up to front) can change relative altitude (up to 500-2500 feet)500-2500 feet)

Barometric pressure decreases as Barometric pressure decreases as altitude rises (hypobaria) and with altitude rises (hypobaria) and with higher latitudeshigher latitudes

Hypobaria decreases the partial Hypobaria decreases the partial pressure of O2: 0.021 x Atm Pressure pressure of O2: 0.021 x Atm Pressure = PiO2, note- [02] remains at 21%= PiO2, note- [02] remains at 21%

Changes in weather (eg: low pressure Changes in weather (eg: low pressure front) can change relative altitude (up to front) can change relative altitude (up to 500-2500 feet)500-2500 feet)