High altitude medicine: Difference between revisions
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==Background== | ==Background== | ||
[[File:Altitude and air pressure & Everest.jpg|thumb|Relationship between total atmospheric pressure and altitude above sea level.]] | |||
===Altitude Stages=== | ===Altitude Stages=== | ||
{| class="wikitable" | {| class="wikitable" | ||
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| align="center" style="background:#f0f0f0;"|'''Physiology''' | | align="center" style="background:#f0f0f0;"|'''Physiology''' | ||
|- | |- | ||
| Intermediate Altitude || | | Intermediate Altitude ||5,000 - 8,000 ft | ||
:(1,524 - 2,438 meters) | |||
|| | |||
*Decreased exercise performance without major impairment in SaO2 | *Decreased exercise performance without major impairment in SaO2 | ||
|- | |- | ||
| High Altitude|| | | High Altitude||8,000 - 12,000 ft | ||
:(2,438 - 3,658 meters) | |||
|| | |||
*Decreased SaO2 with marked impairment during exercise and sleep | *Decreased SaO2 with marked impairment during exercise and sleep | ||
|- | |- | ||
| Very High Altitude ||12,000-18, | | Very High Altitude ||12,000-18,000 ft | ||
:(3,658 - 5,487 meters) | |||
|| | |||
*Abrupt ascent can be dangerous; acclimatization is required to prevent illness | *Abrupt ascent can be dangerous; acclimatization is required to prevent illness | ||
|- | |- | ||
| Extreme Altitude ||>18, | | Extreme Altitude ||>18,000 ft | ||
:(>5,500 meters) | |||
|| | |||
*Only experienced by mountain climbers; accompanied by severe hypoxemia and hypocapnia | *Only experienced by mountain climbers; accompanied by severe hypoxemia and hypocapnia | ||
*Sustained human habitation is impossible | *Sustained human habitation is impossible | ||
*RV strain, intestinal malabsorption, impaired renal function, polycythemia | *RV strain, intestinal malabsorption, impaired renal function, polycythemia | ||
|} | |} | ||
Height of Mount Everest (tallest in world): 29,035 feet (8,850 meters) | |||
Height of Mount Whitney (tallest in contiguous US): 14,505 feet (4,421 meters) | |||
Conversion: 1 meter = ~3.28 feet [https://www.metric-conversions.org/length/meters-to-feet.htm (calculator)] | |||
==Physiology of Acclimatization== | ==Physiology of Acclimatization== | ||
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**Vigor of this inborn response relates to successful acclimatization | **Vigor of this inborn response relates to successful acclimatization | ||
*Initial hyperventilation is attenuated by respiratory alkalosis | *Initial hyperventilation is attenuated by respiratory alkalosis | ||
**As renal excretion of bicarb compensates for | **As renal excretion of bicarb compensates for respiratory alkalosis, pH returns toward normal | ||
*Process of maximizing ventilation culminates within 4-7 days at a given altitude | *Process of maximizing ventilation culminates within 4-7 days at a given altitude | ||
**With continuing ascent the central chemoreceptors reset to ever lower values of PaCO2 | **With continuing ascent the central chemoreceptors reset to ever lower values of PaCO2 | ||
**Completeness of acclimatization can be gauged by partial pressure of arterial CO2 | **Completeness of acclimatization can be gauged by partial pressure of arterial CO2 | ||
**Acetazolamide, which results in bicarb diuresis, can facilitate this process | **[[Acetazolamide]], which results in bicarb diuresis, can facilitate this process | ||
===Blood=== | ===Blood=== | ||
*Erythropoietin level begins to rise within 2 days of ascent to altitude | *Erythropoietin level begins to rise within 2 days of ascent to altitude | ||
*Takes days to weeks to significantly increase red cell mass | *Takes days to weeks to significantly increase red cell mass | ||
**This adaptation is not important for the | **This adaptation is not important for the initial acclimatization process | ||
===Fluid Balance=== | ===Fluid Balance=== | ||
*Peripheral venoconstriction on ascent to altitude causes increase in central blood volume | *Peripheral venoconstriction on ascent to altitude causes increase in central blood volume | ||
**This leads to decreased ADH | **This leads to decreased ADH → diuresis | ||
**This diuresis, along with bicarb diuresis, is considered a healthy response to altitude | **This diuresis, along with bicarb diuresis, is considered a healthy response to altitude | ||
***One of the hallmarks of AMS is antidiuresis | ***One of the hallmarks of AMS is antidiuresis | ||
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===Cardiovascular System=== | ===Cardiovascular System=== | ||
*SV decreases initially while HR increases to maintain CO | *SV decreases initially while HR increases to maintain CO | ||
*Cardiac muscle in healthy patients can withstand extreme hypoxemia | *Cardiac muscle in healthy patients can withstand extreme hypoxemia without ischemic events | ||
*Pulmonary circulation constricts | *Pulmonary circulation constricts with exposure to hypoxia | ||
**Degree of pulmonary | **Degree of pulmonary hypertension varies; a hyper-reactive response is associated with [[High altitude pulmonary edema|HAPE]] | ||
==Differential Diagnosis== | ==Differential Diagnosis== | ||
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==High Altitude Syndromes== | ==High Altitude Syndromes== | ||
[[File:Altitude flow sheet.png|thumb|High altitude management algorithm.]] | |||
*All caused by hypoxia | *All caused by hypoxia | ||
*All are seen in rapid ascent in unacclimatized patients | *All are seen in rapid ascent in unacclimatized patients | ||
**Hypoxemia is maximal during sleep; the altitude in which you sleep is most important | **Hypoxemia is maximal during sleep; the altitude in which you sleep is most important | ||
**Above 10,000ft rule of thumb is to sleep no higher than | **Above 10,000ft rule of thumb is to sleep no higher than 1,000 additional ft/day | ||
*All respond to O2/descent | *All respond to O2/descent | ||
{{Expected SpO2 at altitude}} | |||
==See Also== | ==See Also== | ||
Latest revision as of 21:32, 1 May 2024
Background
Altitude Stages
| Stage | Altitude | Physiology |
| Intermediate Altitude | 5,000 - 8,000 ft
|
|
| High Altitude | 8,000 - 12,000 ft
|
|
| Very High Altitude | 12,000-18,000 ft
|
|
| Extreme Altitude | >18,000 ft
|
|
Height of Mount Everest (tallest in world): 29,035 feet (8,850 meters)
Height of Mount Whitney (tallest in contiguous US): 14,505 feet (4,421 meters)
Conversion: 1 meter = ~3.28 feet (calculator)
Physiology of Acclimatization
Ventilation
- Increased elevation → decreased partial pressure of O2 → decreased PaO2
- Hypoxic ventilatory response results in ↑ ventilation to maintain PaO2
- Vigor of this inborn response relates to successful acclimatization
- Initial hyperventilation is attenuated by respiratory alkalosis
- As renal excretion of bicarb compensates for respiratory alkalosis, pH returns toward normal
- Process of maximizing ventilation culminates within 4-7 days at a given altitude
- With continuing ascent the central chemoreceptors reset to ever lower values of PaCO2
- Completeness of acclimatization can be gauged by partial pressure of arterial CO2
- Acetazolamide, which results in bicarb diuresis, can facilitate this process
Blood
- Erythropoietin level begins to rise within 2 days of ascent to altitude
- Takes days to weeks to significantly increase red cell mass
- This adaptation is not important for the initial acclimatization process
Fluid Balance
- Peripheral venoconstriction on ascent to altitude causes increase in central blood volume
- This leads to decreased ADH → diuresis
- This diuresis, along with bicarb diuresis, is considered a healthy response to altitude
- One of the hallmarks of AMS is antidiuresis
Cardiovascular System
- SV decreases initially while HR increases to maintain CO
- Cardiac muscle in healthy patients can withstand extreme hypoxemia without ischemic events
- Pulmonary circulation constricts with exposure to hypoxia
- Degree of pulmonary hypertension varies; a hyper-reactive response is associated with HAPE
Differential Diagnosis
High Altitude Illnesses
- Acute mountain sickness
- Chronic mountain sickness
- High altitude cerebral edema
- High altitude pulmonary edema
- High altitude peripheral edema
- High altitude retinopathy
- High altitude pharyngitis and bronchitis
- Ultraviolet keratitis
High Altitude Syndromes
- All caused by hypoxia
- All are seen in rapid ascent in unacclimatized patients
- Hypoxemia is maximal during sleep; the altitude in which you sleep is most important
- Above 10,000ft rule of thumb is to sleep no higher than 1,000 additional ft/day
- All respond to O2/descent
Expected SpO2 and PaO2 levels at altitude[1]
| Altitude | SpO2 | PaO2 (mm Hg) |
|---|---|---|
| 1,500 to 3,500 m (4,900 to 11,500 ft) | about 90% | 55-75 |
| 3,500 to 5,500 m (11,500 to 18,000 ft) | 75-85% | 40-60 |
| 5,500 to 8,850 m (18,000 to 29,000 ft) | 58-75% | 28-40 |
See Also
References
- ↑ Gallagher, MD, Scott A.; Hackett, MD, Peter (August 28, 2018). "High altitude pulmonary edema". UpToDate. Retrieved May 2, 2019.