Transcript Anesthesia and Altitude - International Society of Chronic

Anesthesia and Altitude
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Physics and Physiology of Altitude
 Definitions
○ High Altitude=1500 to 3500m
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Onset of physiologic effects of diminished Fio2. minor impairment of Sao2 (typically 9095%). Increased minute ventilation and decreased PaCo2 at rest
○ Very High Altitude= 3500 to 5500m
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SaO2 falls below 90% and PaO2 falls below 60mm Hg
Extreme hypoxia may occur during sleep exercise or high altitude illness
○ Extreme Altitude= over 5500em
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Significant hypoxia and hypocapnia exist. Deterioration of physiologic function will occur.
Permanent habitation can not exist
Anesthesia and Altitude
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Physics and Physiology of Altitude
 Previous Medical Research
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Serious research started in the late 1940’s and early 1950’s as Mount Everest
became the worlds foremost goal in Mountaineering. The English and other
Europeans pioneered the research in a quest to summit Mount Everest. Initiated
studies of Oxygen flow requirements for >8000m
Mt Logan 1967-1969 Charles Houston MD AMS and HAPE
Work of Carlos Monge ( South America) was pivotal in the field of chronic
altitude physiology.
Silver Hut research Sir Edmund Hilliary James West MD and Griffith Pugh
7440m Makalu
1982 AMREE Frank Sarnquist MD et al. First to measure alveolar gases and
barometric pressure on Mt. Everest Summit
1982-1990 Denali Medical research project Peter Hacket MD
Operation Everests I and II 1985
Himalayan Rescue Association Pheriche Khumbu Nepal
Anesthesia and Altitude
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Environment at High Altitude
 Barometric Pressure falls with increasing altitude in logarithmic
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fashion.
Therefore partial pressure of oxygen also falls (21% of
Barometric pressure (BP).
Causes Hypoxia. The primary problem. Example: Barometric
Pressure is 50% at 5500m
Related to position relative to equator
Extreme cold fronts also cause a drop in BP.
Anesthesia and Altitude
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Physics and Physiology
 Ventilation changes
○ Hypoxic Ventilatory response (HVR) is key
○ Hypoxia is profound enough to trigger ventilation not hypercarbia!!
○ Therefore, hyperventilation (relative to normal Carbon Dioxide levels)
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occurs. This drops the CO2 levels profoundly. Carotid body senses
the decrease PaO2, triggers respiratory center in Medulla to increase
ventilation.
HVR is genetically determined. Not significantly improved by
exercise.
HVR decreased by ethanol, benzodiazepines, narcotics.
HVR improved by Acetazolamide (Diamox) caffeine and cocaine
Causes a primary respiratory alkalosis reachs maximal effect at 7
days. Plasma HCO3- drops!!
Anesthesia and Altitude

Physics and Physiology
 Chronic Altitude Polycythemia
○ Rise in Hemoglobin levels in response to
chronic hypoxia
○ First described by Carlos Monge
○ Leads to a higher viscosity of blood
○ Higher level of DVT’s??
Anesthesia and Altitude
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Physics and Physiology
 Circulation Changes
○ Systemic Circulation:
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mild increase in Blood Pressure.
Moderate increase in heart rate
Moderate increase in cardiac output
Heart rate returns to normal with acclimatization
○ Pulmonary Circulation
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Hypoxic pulmonary vasoconstriction causes increase PA pressures
Not a complete return to normal with supplemental O2.
○ Cerebral circulation
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Balance of Hypoxic vasodilation and hypocapnic vasoconstriction
Anesthesia and Altitude
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Physics and Physiology
 Hemopoietic changes
○ Research first done in 1890 in the Andes showed a increase level of
hemoglobin.
○ Hypoxia causes erythropoietin secretiion. This causes bone marrow
production of red blood cells.
○ RBC released as early as 5 days and occurs for several weeks.
○ Early rise in HgB level is due to decreased plasma levels
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The practice of Medicine at High and
Extremely high Altitude
 Illnesses Aggravated by High Altitude
○ Chronic Lung Disease
○ Arteriosclerotic Heart Disease
○ Hypertension
○ Sickle Cell Disease
○ Pregnancy
The practice of Medicine and Anesthesia at High and
Extremely high Altitude
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Illnesses aggravated by high altitude
 Chronic Lung Disease:
○ COPD: Reduced exercise capability. Hypoxemia, pulmonary
hypertension can be expected to worsen. If SaO2 is <85% at sea
level, reccommend supplemental oxygen. 1920m shown to be well
tolerated.
○ Pulmonary Hypertension: Increased incidence of HAPE. Travel to
high altitude is contraindicated.
○ Obstructive sleep apnea: May become severely hypoxic at
altitude. Periodic breathing cheyenne stokes respiration is worsened.
○ Asthma: Can be aggravated by airway heat loss of altitude,
however, problems are quite unusual. Not a contraindication to travel
to altitude but recommend bringing all medications
The practice of Medicine at High and Extremely
high Altitude
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Arteriosclerotic Heart Disease
 Healthy heart has been shown to tolerate extremely high altitude without
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problems. Shown by electrocardiogram, echocardiograms, heart
catheterizations and exercise stress tests.
Little clear evidence as yet for increased cardiac ischemic events in
patients with history of ischemic cardiovascular disease.
Moderate altitude is tolerated, with reduced levels of exercise.
High and very high altitude is not reccomended.
Patients with CABG who are asymptomatic and have normal stress tests
have successfully completed climbs over 5200m
The practice of Medicine at High and Extremely
high Altitude
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Hypertension
 A small and transient rise in blood pressure
is seen on travel to high altitude.
 A similar rise occurs in patients with preexisting hypertension
 Reccomendations to continue with current
medications make sense. What about
diuretics??
The practice of Medicine at High and Extremely
high Altitude
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Sickle cell anemia
 Sickle cell crisis is well known complication of exposure to
high altitude
 20% incidence of crisis in patients with hemoglobin SC
with travel to 1500-2000m
 Splenic infarction syndrome more common,
The practice of Medicine at High and
Extremely high Altitude
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Pregnancy
 Limited data exist
 Higher incidence of pregnancy induced hypertension and pre-
eclampsia
 No documented increase in spontaneous abortion, placenta
abruption, placenta previa,
 No fetal heart rate changes appear evident at moderate altitude.
Airplane travel is okay but >4000m is not reccomeded
The practice of Medicine at High and
Extremely high Altitude
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The practice of Medicine at High and Extremely high Altitude
 Advisability of Exposure to High and Very High Altitude for
common conditions
Anesthesia and Altitude
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The practice of Anesthesia at Altitude
 Pre-existing medical conditions and
anesthesia
 Reduced Partial pressure of Oxygen at
altitude and hypoxia with anesthesia
 N2O at Altitude
The practice of Anesthesia at Altitude
Pre-existing medical conditions and anesthesia
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CAD
Congestive Heart Failure
HTN
Serious Arrhythmias
Cerebro-Vascular disease
Sickle Cell Anemia
Pulmonary Conditions
Pulmonary Hypertension
OSA
Pregnancy
The practice of Anesthesia at Altitude
Reduced Barometric pressure causes a reduced partial pressure of
oxygen. Causes an underlying hypoxic precursor. Once patient is
intubated and ventilated in a semi-closed circuit the percentages of
inhaled gases can be tightly controlled but the reduced barometric
pressure remains the same. If patient is undergoing Intravenous
sedation or regional anesthetic, then they are subjected to lower
partial oxygen tension.
 Typically this does not cause a significant problem in healthy
individuals. Can lead to issues in patients with underlying diseases
as previously discussed.
 Inspired oxygen content is titrated to effect
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The practice of Anesthesia at Altitude
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Using Nitrous Oxide at altitude. Remember that the relative
ratios of all gases remain the same. The total number of
molecules in a given space is diminshed with reduced
pressure. Typically our concern is simply with reduced
barometric pressure causing an insuffcient oxygen delivery
to meet the metabolic needs of the tissue.
We recommend not delivering more than 50% Nitrous oxide
over 2500m
Anesthesia and Altitude
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Case Report #1
 43 year old male for urgent laparoscopic cholecystectomy
 Obstructive sleep apnea
 Morbid obesity
 Lives at sea level
 Smokes ½ pack per day
 Has a room air SpO2 = 83%, RR=26
 He complains of pain despite being apparently over
sedated by emergency room
Anesthesia and Altitude
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Case Report #2
 75 year old female
 smoker,
 COPD,
 Known coronary artery disease.
 History of Congestive heart failure in past
 Lives at sea level.
 Has fallen, fractured her hip and now needs
open reduction internal fixation of fracture