High Altitude Medical Problems

Resident RoundsGarth Smith R3Feb 25, 2010

thanks to Shawn Dowling, Chris Hall

Objectives

• Review some physiology and terminology

• Recognition, Treatment, Risk Factors, and Prevention of High Altitude Syndromes

• high altitude decompression of airplanes

• secretly make use of the Gas Laws

• Not covering Illnesses Aggravated by High Altitude, hypothermia, trauma, frostbite, avalanches, lightning

Case 1

• 24y male trekking with friends

• 20-night trek including a pass @ 5,400m

• During 8th day c/o headache at dinner (4,000m)

• Has poor sleep but awakes feeling well enough to continue

• Continues hiking and by mid-morning has H/A again and has vomited twice (now at 4,150m)

Case 2

• 20yo male porter

• Camped at 4,930m after crossing a steep, technical pass at 5,120m and awoke with significant exercise intolerance and a cough

• Descended with the group and camped at 3,800m feeling significant improvement

• The following morning had severe dyspnea at rest; was unable to carry his load

• Arrives at a volunteer clinic being carried by his colleagues; resting O2 sat 48% on room air

Summary

• go up slow, sleep low, take it easy, consider taking meds prophylactically if at risk

• if kinda sick: find a friend, rest, don’t ascend, and consider meds. ascend when no symptoms.

• if sick: find a friend, descend, and use meds.

• if really sick: a friend will find you, they will get you down fast, and they will use meds on you.

• oxygen is good. portable HBOT is wise.

• the mountain will be there tomorrow.

What mtn am I on?

How high is high?intermediate1500-2500m

high 2500 - 4200m

very high 4200 - 5500m

extreme >5500m

“dead zone” >7600m

Who wrote this book?

Who is this guy?

What’s the problem• High altitude is a

hypoxic environment!

• hypoxia is bad

• we need oxygen to live

What is the concentration of oxygen at sea level? 5000m above sea

level?

both have 21% O2 but I’d get more O2 on the

right if delivered at twice the pressure

Hey...we just used the ideal gas law

same volumesame temp

same concentration but twice the mass

= ? x pressure

Gas Laws

• Boyle’s Law

• Dalton’s Law

• Henry’s Lawthe solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid

Hypoxia

• Partial pressure of oxygen decreases as a function of the barometric pressure

Hey...we just used Dalton’s law!

What SaO2% or PaO2 makes you worried?

What’s the problem

• High altitude is a hypoxic environment because of hypoxemiaAltitude (m) Barometric Pressure

(mmHg)PaO2 (mmHg) SaO2% PaCO2 (mmHg)

sea level 760 90-95 96% 40

1500 640 75-81 95% 36

2300 580 69-74 93% 32

4500 445 48-53 86% 25

6000 370 37-45 76% 20

7600 300 32-39 68% 13

8900 252 26-33 58% 10

Hyp

oxem

ia

If PaO2 is halved when Barometric Pressure is doubled, why isn’t SaO2%

halved?

75

Below what Osat would someone rapidly deteriorate and become

unconscious?

75

60

8900 252 26-33 58% 10

Why is the pressure lower at altitude?

Pressure = force / area

more mass = more force = more pressure

What happens when you are exposed to low

PiO2 • increased ventilation

• make more blood

• diuresis

• ↑sympathetic tone

• ↑pulmonary pressure

improve arterial and cellular oxygenation

Ventilation

• hypoxic ventilatory response (HVR)

• effected by the carotid body - senses ↓paO2

• resp center in medulla ↑RR

• effected by chronic hypoxia, ETOH, resp suppresants (benzos, opiods)

• culminates after 4 -7 d

• central chemoreceptors reset to progressively lower PCO2

Acclimatization

• The process by which individuals gradually adjust to hypoxia and enhance survival and performance

• 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, beyond that progressive deterioration occurs

Definition• “high-altitude illness” (HAI) is used to describe

the cerebral and pulmonary syndromes that can develop in unacclimatized persons shortly after ascent to high altitude.

HAPEAMS → HACE

Pathophysiology

Name 4 risk factors for the development of HAI

Risk factors

• fast ascent, high altitude reached, high sleeping altitude

• a history of HAI

• residence at an altitude below 900 m

• physical exertion, cold

• preexisting pulmonary hypertension, low hypoxic ventilatory response and low vital capacity

Epidemiology

• age has little influence on incidence but persons >50 may have some protection

• physical fitness has no bearing on susceptibility to HAI

• women are equally at risk for AMS/HACE but less susceptible to HAPE

• HAI is reproducible in an individual on repeated exposures; suggesting some unknown genetic risk factors

I’ll never see that...Study Group # at Risk per

YearSleeping 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) ?

AMS → HACE

• Acute Mountain Sickness (AMS) and High Altitude Cerebral Edema (HACE) are considered a spectrum of the same pathophysiological process

• HACE is the end-stage of AMS.

what three criteria must be met in all cases of AMS?

AMS

Lake Louise Consensus Group says

AMS is

1) headache in

2) unacclimatized person

3) at altitude >2500m

4) plus one or more of: GI symptoms, insomnia, dizziness, lassitude, or fatigue

HACE

• defined as the onset of ataxia, altered consciousness (drowsiness is commonly followed by stupor), or both in someone with acute mountain sickness or high-altitude pulmonary edema.

• In those who also have high-altitude pulmonary edema (HAPE), severe hypoxemia can lead to rapid progression from acute mountain sickness to high-altitude cerebral edema.

• The cause of death is brain herniation.

AMS → HACE Pathophysiology

Name 4 classes of medications used in the treatment of AMS → HACE

Prophylaxis

• ASA 325 Q4 x 3 dose (HA only)

• Acetazolamide 125-250 BID

• slow ascent

• meds not for everyone (risk of unknown sulfa allergy)

• consider if prev history of AMS at low/mod altitude, or forced rapid ascent (flying to high elevation)

Treatment

Mild Symptoms of AMS

•Does not need descent if mild Sx and constant supervision

•Stop ascent until better

•Acetazolamide (250 BID)

•Tylenol/ASA/NSAID for HA

•Anti-emetic PRN

•Consider O2(1-2L)

•May ascend after Sx resolve

•Avoid things that limit HVR

Moderate or Unresolving AMSDescend 500 m, if not possibleO2 at 1-2 LPMHyperbaric therapyDexamethasone 4mg PO/IV/IM q6h

•Acetazolamide (250 BID)May ascend after symptoms resolve

Treatment

HACE

•Initiate immediate descent or evacuation

•if descent is not possible, use a portable hyperbaric chamber

•administer oxygen (2 to 4 liters/min)

•administer dexamethasone (8 mg orally, intramuscularly, or intravenously initially, and then 4 mg every 6 hr)

•administer acetazolamide if descent is delayed

Rebound

• Acetazolamide “cures” AMS, discontinuation does not risk rebound of symptoms, unless you climb higher

• Dexamethasone improves AMS→HACE but does not cure it. discontinuation can induce rebound symptoms and clinical deterioration even at constant altitude

Gamow Bag

Portable Hyperbaric Chamber

• pronounced “Gam-Off”, Dr. Igor Gamow

• Lightweight (14.9 lb), costly ($2400US)

• Manually pressurized

• Generate 100mm Hg above ambient pressure

• Simulates descent of 1,500m at moderate altitudes

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

• duration - AMS - 2 hrs, HAPE - 4hrs, HACE - 6hrs

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

What’s the problem

Altitude (m) Barometric Pressure (mmHg)

PaO2 (mmHg) SaO2% PaCO2 (mmHg)

sea level 760 90-95 96% 40

1500 640 75-81 95% 36

2300 580 69-74 93% 32

4500 445 48-53 86% 25

6000 370 37-45 76% 20

7600 300 32-39 68% 13

8900 252 26-33 58% 10

Hyp

oxem

ia

Dr. Gamow’s father George was a famous physicist. What did theory did he co-

author

How does acetazoladmide help with AMS → HACE?

AMS → HACE Pathophysiology

How does dexamethasone help with AMS → HACE?

AMS → HACE Pathophysiology

Myths

• Coca leaves for Machu Picchu

• Ginko Baloba helps/prevents

• overhydration prevents

HAPE

• High Altitude Pulmonary Edema (HAPE)

• this is the killer - accounts for most deaths from high-altitude illness

• commonly strikes the second night at a new altitude (sneaky)

• rarely occurs after more than four days at a given altitude

Diagnosis

• Early diagnosis is critical.

• In the proper setting, decreased performance and a dry cough should raise suspicion

Diagnosis

≥2 symptoms:

•Dyspnea at rest

•Cough

•Weakness or decreased exercise performance

•Chest tightness or congestion

≥2 signs:Central cyanosisAudible crackles or wheezing in at least one lung fieldTachypneatachycardia

•fever

HAPE Pathophysiology

Treatment

• Increasing alveolar and arterial oxygenation is the highest priority

• descent and supplemental O2

• Medication is necessary only when supplemental oxygen is unavailable or descent is impossible

Medications

Prevention

•Nifedipine ER 30mg PO Q12h

•Salmeterol 1-2p BID

•Acetazolamide 250mg PO BID

•slow ascent, stay warm, avoid ETOH/sleeping pills/narcotics

Temporizing O2, PEEP

•Nifedipine IR 10mg then ER 30mg Q12h

•HBOT

•Salmeterol

•Sildenafil 20mg PO TID

•Acetazolamide

Case 1

• 24y male trekking with friends

• 20-night trek including a pass @ 5,400m

• During 8th day c/o headache at dinner (4,000m)

• Has poor sleep but awakes feeling well enough to continue

• Continues hiking and by mid-morning has H/A again and has vomited twice (now at 4,150m)

Case 1

• What is the diagnosis?

• Does this person need to descend?

• What other treatment options are available?

AMS

• Lake Louise Consensus Group says

• AMS is

1) headache in

2) unacclimatized person

3) at altitude >2500m

4) plus one or more of: GI symptoms, insomnia, dizziness, lassitude, or fatigue

Mild Symptoms of AMS

• Does not need descent if mild Sx and constant supervision

• Stop ascent until better

• Acetazolamide 250mg PO BID

• Tylenol/ASA/NSAID PRN for HA

• Anti-emetic PRN

• Consider O2 (1-2L/min)

• May ascend after Sx resolve

• Avoid things that limit HVR

Case 1, part 2

• The patient manages to continue with the group

• Spends the 8th night at 4,600m, occasionally vomits

• On awakening is still unwell but persuaded by his friends to continue

• On arrival at the ‘base camp’ at 4,830m, the patient is too ataxic to continue and seems confused

• His friends are attempting to hire a horse to continue up the pass when you arrive…

Case 1, part 2

• What is the diagnosis now?

• What would the correct course of action have been on the second morning (4,600m)?

• What adjunctive therapies might help at this point?

• A makeshift clinic is present at the 4,830m camp with a supply of oxygen. Darkness has fallen and the patient is too ataxic to walk.

• How would you approach this problem?

Case 1, part 2

• HACE

• with unresolving or worsening AMS, should have descended 500m and stopped to acclimatize until symptom free

• now with HACE and descent not possible, he needs O2, dex, acetazolamide and a Gamow bag

Case 2

• 20yo male porter

• Camped at 4,930m after crossing a steep, technical pass at 5,120m and awoke with significant exercise intolerance and a cough

• Descended with the group and camped at 3,800m feeling significant improvement

• The following morning had severe dyspnea at rest; was unable to carry his load

• Arrives at a volunteer clinic being carried by his colleagues; resting O2 sat 48% on room air

Case 2

• What is the diagnosis?

• What is the most important treatment?

• What other treatments should also be initiated at this time?

• Helicopter evacuation is impossible and the solar-powered O2 concentrator has been depleted. Evacuation on foot will entail a 35km walk in darkness.

• How would you approach this problem?

HAPE

≥2 symptoms:

•Dyspnea at rest

•Cough

•Weakness or decreased exercise performance

•Chest tightness or congestion

≥2 signs:Central cyanosisAudible crackles or wheezing in at least one lung fieldTachypneatachycardia

•fever

Case 2

• He needs to get down ASAP but unadvisable to travel at night...unless ?

• Temporizing measures include O2, PEEP, Nifedipine, HBOT, Salmeterol, Sildenafil, Acetazolamide

Take Home Points

• high altitude is a hypoxic environment

• any illness at altitude is altitude illness until proven otherwise

• early recognition is key

• never ascend if symptoms of AMS

• if deteriorating, descend immediately

• if unsure, descend. tackle that mountain another day.

Resources

• Tintinalli. Emergency Medcine.

• Auerbach. Wilderness Medicine.

• Gertsch, J. Randomised, double blind, placebo controlled comparison of ginkgo biloba and acetazolamide for prevention of acute mountain sickness among Himalayan trekkers: the prevention of high altitude illness trial (PHAIT). BMJ. 328;797, 2004

• Hackett, P.H. High-Altitude Illness. NJEM.Vol. 345, No. 2. July 12, 2001

• Sartori, C. Salmeterol for the Prevention of High Altitude Pulmonary Edema. NJEM, Vol. 346, 2002

• Dowling’s Rounds from 2009