Download Altitude (m) - Calgary Emergency Medicine

High Altitude Medical
Problems
Resident Rounds
Garth Smith R3
Feb 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?
• intermediate
• 1500-2500m
• high
• 2500 - 4200m
• very high
• 4200 - 5500m
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?
same volume
same temp
same concentration
but twice the mass
= ? x pressure
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
Gas Laws
• Boyle’s Law
• Dalton’s Law
• Henry’s Law
the 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
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
Hypoxemia
because of hypoxemia
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.
AMS → HACE
HAPE
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
Year
Sleeping
Altitude
% AMS
(# affected)
% HAPE
or HACE
40 Million
2400-2800
meters
15 (6 million)
.01(4000?)
Mt. Everest
Trekkers
6,000
3000-5200
meters
35 (2100)
1.0 (60?)
Mt. McKinley
Climbers
1,200
3000-5300
meters
30 (300)
2-3 (25-35)
Mt. Rainier
Climbers
9,000
3000
meters
67 (6000)
?
Western USA
Visitors
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 highaltitude 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
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
Hypoxemia
What’s the problem
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:
•≥2 signs:Central
• Dyspnea at rest
cyanosisAudible crackles
or wheezing in at least one
lung
fieldTachypneatachycardia
• Cough
• Weakness or
decreased exercise
performance
• Chest tightness or
congestion
•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
•Temporizing O2,
• Nifedipine ER 30mg PO
PEEP
Q12h
• Salmeterol 1-2p BID
• Acetazolamide 250mg
PO BID
• slow ascent, stay warm,
avoid ETOH/sleeping
pills/narcotics
•Nifedipine IR 10mg
then ER 30mg Q12h
•HBOT
•Salmeterol
•Sildenafil 20mg PO
TID
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 solarpowered O2 concentrator has been depleted.
Evacuation on foot will entail a 35km walk in
darkness.
• How would you approach this problem?
HAPE
• ≥2 symptoms:
•≥2 signs:Central
• Dyspnea at rest
cyanosisAudible crackles
or wheezing in at least one
lung
fieldTachypneatachycardia
• Cough
• Weakness or
decreased exercise
performance
• Chest tightness or
congestion
•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