An Unofficial Acclimatization Guideline for JMT Hikers Things to consider when planning your John Muir Trail hike Leslie Rozier, DNP, APRN, Inga Aksamit, RN-BC, MBA and Kenny Meyer

The following guideline provides basic information about the illnesses triggered by the reduced oxygen content of air found at the higher elevations on the John Muir Trail and other parts of the Sierra Nevada in California, and recommendations for how to avoid an altitude illness.

Table of Contents Why should you care about this guideline? .............................................................. 1 What is ‘high altitude’? ............................................................................................. 2 What happens in the body when the oxygen level changes (simple version)? ......... 3 What is altitude illness? ............................................................................................ 4 Who gets an altitude illness?..................................................................................... 7 How is AMS recognized? ......................................................................................... 9 What can be done to prepare? ................................................................................... 9 What is the best way to acclimatize? ...................................................................... 10 Acclimatization FAQ .............................................................................................. 12 An example JMT plan with acclimatization ........................................................... 19 Summary ................................................................................................................. 23 About the authors .................................................................................................... 23 References ............................................................................................................... 23 Appendix I. Data Tables....................................................................................... 26

Why should you care about this guideline?  

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All travelers to altitude are at risk for developing an altitude related illness. Symptoms of altitude illness typically appear above 8,200 feet [1] but can present at elevations as low as 6,500 feet [5]. Symptoms of altitude illnesses include Acute Mountain Sickness (AMS), High Altitude Cerebral Edema (HACE) and High Altitude Pulmonary Edema (HAPE). Symptoms of altitude illness vary widely and can be difficult to identify. Many symptoms of altitude illness can appear within 6 to 10 hours of exposure to altitude. The most severe and dangerous forms of the illness may not appear for 1 to 4 days. Unattended altitude illness can be fatal.

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Copyright (c) 2014, 2015, Leslie Rozier, Inga Aksamit, Kenny Meyer Verbatim copies of this document may be copied and redistributed but only under the following conditions: 1) The document is copied or redistributed in its entirety, 2)the document has not been changed in any form and 3)each copy includes an attribution to the authors. You can contact the authors by emailing [email protected].

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If the ascent rates suggested in these acclimatization guidelines are followed, hikers will be less susceptible to, and may avoid any symptoms of, altitude illness. There are medications that may help with acclimatization but are not replacements for gradual ascent. The John Muir Trail (JMT) hiker will spend many days and nights at high altitude: o The majority of the trail lies above 8,000 feet o The trail summits at 14,500 feet on top of Mt. Whitney o Six of the ten passes are over 11,000 feet o The average elevation of the trail south of Lyell Forks in Yosemite, over 80% of the hike, is over 10,000 feet1

What is ‘high altitude’? As altitude increases so does the stress on the body; the higher the elevation the greater the stress. In order to characterize the increasing physiologic stress, “high altitude” is typically divided into three categories [3]: 

High altitude: 4,921 to 11,483 feet (1,500 to 3,500 meters) High-altitude illness is common with abrupt ascent to or above 8,202 feet (2500 meters). Decreased exercise performance and increased ventilation are also common. There is only minor impairment in the body’s oxygen saturation. The lower elevations of the JMT and the first five passes, starting from the north, fall into this category.

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Very high altitude: 11,483 to 18,045 feet (3,500 to 5,500 meters) This is the most common range for severe high-altitude illness. Abrupt ascent may be dangerous and a safe ascent may require a period of acclimatization. The blood’s oxygen saturation can drop by 15-25%, causing extreme hypoxia, which may occur during sleep or exercise. Five of the JMT mountain passes fall into this category.

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Extremely high altitude: 18,045 to 29,035 feet (5,500 to 8,850 meters) The body is unable to acclimatize to extremely high altitude and a progressive deterioration of physiologic function eventually outstrips acclimatization. The blood’s oxygen saturation drops by 25-42%. Abrupt ascent almost always precipitates severe high-altitude illness. The JMT never reaches extremely high altitude. Locations at this extreme elevation include Mt. Kilimanjaro in Tanzania (19,341 feet; 5,895 meters) and Mt. Everest in Nepal (29,029 feet; 8,848 meters).

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Based on data from Wenk’s spreadsheet [10]

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As the elevation increases, the barometric pressure drops. As the barometric pressure decreases, so does the amount of atmospheric oxygen. The oxygen portion of the air pressure is called its partial pressure. Figure 1 shows the linear correlation between barometric pressure and oxygen partial pressure drop with elevation gain. Note that the oxygen partial pressure at Mt. Whitney (~14,500 feet) is only 60% of the oxygen available at sea level. (see Appendix I for references to source data) Figure 1: Oxygen content of the air drops rapidly with elevation

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Atmospheric oxygen partial pressure (mmHg)

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Changes in Barometric Pressure and O2 Pressure with Elevation

Elevation (ft) Barometric Pressure (mmHg)

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In addition to the effects of high elevation, low-pressure weather systems may further reduce the available atmospheric oxygen the equivalent of an additional ascent of a few hundred to several thousand feet [3].

What happens in the body when the oxygen level changes (simple version)? When we inhale oxygen from our environment, our breath brings oxygen into the lung, specifically the alveoli, where it diffuses through the alveolar wall into the tiny blood vessels called pulmonary capillaries. The oxygen is transported through the blood vessels back to the heart and then carried to the tissues throughout the body. When oxygen levels fall, a chain of physiological events follows: blood flow to the brain increases, the heart works harder and respirations increase. Symptoms may include: headache, nausea, loss of appetite, fatigue, weakness, dizziness and difficulty sleeping.

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Figure 2: O2 saturation of blood hemoglobin drops as partial pressure drops (see Appendix I for references to source data)

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Note: For more information about the physiology of oxygen transport, we recommend the following resources.  “Going Higher, Man, and Mountains,” Part II of by Charles Houston.[21]  “Regulation of Tissue Oxygen,” from the National Center for Biotechnology Information by Roland Pittman [22]  “All about Oxygen,” a Critical Care Medicine Tutorial by Patrick Neligan [23]

What is altitude illness? Altitude illness is the body’s maladaptive response to the reduction of oxygen at higher altitudes [13]. The amount of oxygen in the air decreases with elevation, i.e. as the air thins, we inhale fewer oxygen molecules with each breath. As the amount of oxygen in the air (atmospheric oxygen) decreases, the blood oxygen saturation drops (see Figure 2), creating a low oxygen state known as hypoxemia.2 Almost every organ system in the body undergoes changes with exposure to high altitude. The adaptive physiological adjustment of the body to hypoxemia is called acclimatization. The completion of acclimatization is often referred to as being acclimated. Sometimes the terms get used interchangeably but both address the physiologic effort needed to adjust to a decrease in oxygen caused by an increase in altitude.

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Some references will refer to hypoxia and hypobaric hypoxia as well as hypoxemia. Hypoxia or low blood oxygen refers broadly to diminished availability of oxygen to body tissues. Hypobaric hypoxia is a condition where the body is deprived of a sufficient supply of oxygen from the environment. Hypoxemia refers to low blood oxygen i.e. the decrease in blood oxygen saturation.

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Initial type of high-altitude illness 

Acute Mountain Sickness (AMS) AMS symptoms are typically the first sign of hypoxia and commonly experienced by recreational hikers and tourists at high altitudes. AMS typically develops 6 to 10 hours after ascent but sometimes symptoms start as early as 1 hour. The symptoms usually last from 24-48 hours. AMS symptoms may include headache, loss of appetite, nausea or vomiting, fatigue, dizziness and trouble sleeping. Symptoms may be mild as the hiker or tourist adjusts to high altitude. AMS is described as “self-limiting,” i.e., if the symptoms prevent further elevation gain the illness does not progress. If an AMS sufferer continues to ascend, there is danger of a progression to high altitude cerebral edema (HACE) or high altitude pulmonary edema (HAPE).

Severe types of high-altitude illness 

High Altitude Cerebral Edema (HACE) HACE is an advanced and potentially fatal form of AMS caused by edema (swelling) of brain tissues. HACE may be referred to as AMS/HACE since the preventive and treatment measures can be addressed simultaneously [5] AMS/HACE symptoms typically appear 3 to 5 days after the ascent but may occur as early as the first or second day. In some cases, symptoms may show up at elevations as low as 9,000 feet. HACE usually occurs at higher elevations and is reversible if recognized and treated early. AMS/HACE symptoms may include confusion, clumsiness, vision disturbances and stumbling. The first signs may be some kind of uncharacteristic behavior such as lethargy, excessive emotion or violence, and ataxia3 (loss of coordination), first in the lower body, then the upper body. In some cases there may be seizures or hallucinations. HACE may progress from mild to life-threatening within a few hours. Drowsiness and loss of consciousness occur shortly before death due to brain herniation (a condition that occurs when the pressure inside the skull is so great that brain tissue is forcibly displaced) [3]. HACE may also develop from HAPE (see below.) In other words a hiker experiencing HAPE may also experience HACE. HACE does not preclude HAPE and vice versa.

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Clinically, ataxia is defined as uncoordinated movement due to a muscle control problem. It leads to a jerky, unsteady, to-and-fro motion of the middle of the body (trunk) and an unsteady gait (walking style) which is sometimes call the “sailor’s gait.” It can also affect the upper limbs

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High Altitude Pulmonary Edema (HAPE) HAPE is a form of pulmonary edema which is a buildup of fluid in lung tissue. HAPE is the most frequent cause of fatalities resulting from high-altitude illness. HAPE can be triggered by a rapid ascent and heavy exertion. The progression of HAPE symptoms is accelerated by continuous ascent, vigorous exertion and cold temperatures. HAPE usually shows up within 1 to 3 days of arrival at elevation but rarely after 4 days. HAPE symptoms include cough, diminished exercise performance, chest tightness, chest congestion and dyspnea at rest. Dyspnea is shortness of breath or the feeling that one is not getting enough air. Dyspnea is normal after heavy exercise but not if it occurs in unexpected situations or persists despite a reasonable rest period. HAPE typically progresses from a dry cough to a cough producing blood-tinged sputum (sputum is the mucus that is coughed up from the lung). HAPE symptoms appear to vary between both individuals and ascents. Some people appear to have a predisposition to the illness while others may not be at all susceptible. There is a debate in the research community about HAPE susceptibility. The variability between ascents may be due to multiple factors including ascent rate, maximum altitude, barometric pressure, sleeping altitude, duration at altitude, exertion, pre-acclimatization, temperature, prior history, and other medical problems [3].

Less severe effects of altitude 

Altitude Induced Peripheral Edema (AIPE) AIPE is common adverse effect of hypoxemia. “Peripheral edema” simply means swelling of tissues other than internal organs. As the body retains fluids, AIPE may take the form of overall weight gain accompanied by a bloated feeling and clothes feeling tight. While not life-threatening by itself, AIPE is commonly found in people with AMS [15]. Signs of AIPE include swelling of the face, especially notable as puffy eyes and/or swollen hands or feet. Overall weight gain can range from 6 to 12 pounds (4-6 kg) and more, though this is impossible to measure in the backcountry. A hiker with AIPE should be checked for signs of HACE and HAPE and managed appropriately [16].

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High Altitude Retinal Hemorrhage (HARH) Retinal bleeding may occur may occur at high altitude (above 11,975 feet [3650 meters]). It is thought that this is related to dilation of the retinal arteries and veins due to decreases in oxygenation. Symptoms of HARH vary from no symptoms to subtle vision changes to sudden loss of vision (rare). Any vison changes are normally transient but sometimes vision may

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be permanently reduced. Significant visual changes would be justification for not gaining further altitude, or descending until improvement occurs. HARH can be benign and affect otherwise healthy hikers but may be more common in people with AMS. Hikers with HARH should be checked for signs of HACE and HAPE and managed appropriately. [26]

Who gets an altitude illness? The individual who develops an altitude illness usually ascends too rapidly; simply stated they go too high, too fast. The tendency to develop AMS/HACE/HAPE varies between individuals and between ascents. The differences are due to the rate at which people can accommodate reduced oxygen supply. The underlying cause is almost always hypoxemia. A previous history of a high-altitude illness is the most valuable predictor that an individual will suffer symptoms. Ironically, physical fitness does not reduce susceptibility. Vigorous exercise on initial arrival can be detrimental. The Wilderness Medical Society (WMS) has established risk categories for AMS/HACE as a tool for the hiker to assess the risk of a planned ascent. These risk categories appear in Table 1. The following assumptions apply to the descriptions for each risk category:    

Ascents are calculated from the last fully acclimated sleep altitude. For example, if a hiker slept in Lone Pine (3,727) and climbed Whitney (14,505) the ascent would be 10,778 feet. The ascents are assumed to start at elevations < 3,900 feet The risk categories assume that no acclimatization has occurred. The risk categories do not apply to HAPE. The WMS guidelines do not provide a comparable risk table for HAPE.

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Table 1: WMS Risk categories for Acute Mountain Sickness [5] (The altitude measurements have been changed from meters to feet for ease of interpretation.)

Risk Category Low

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Description  Individuals with no prior history of altitude illness and ascending to ≤ 9,190 feet  Individuals who take ≥ 2 days to arrive at 8,200 to 9,840 feet with subsequent increases in sleeping elevation < 1,600 feet/day and an extra day for every 3,280 feet.  Individuals with prior history of AMS and ascending to 8,200 to 9,190 feet in 1 day  No history of AMS and ascending to >9,190 feet in 1 day  All individuals ascending >1,640 feet/day (increase in sleep elevation) at altitudes above 9,840 feet but with an extra day for acclimatization every 3,280 feet.  History of AMS and ascending to > 9,190 feet in 1 day  All individuals with a prior history of HACE  All individuals ascending to > 11,480 feet in 1 day  All individuals ascending > 1,640 feet/day (increase in sleeping elevation) above > 9,840 feet without extra days for acclimatization  Very rapid ascents (e.g. < 7-day ascents of Mt. Kilimanjaro)

Here’s an example of a “low risk" plan for a hiker who has never had AMS: 1. Starts day 1 at sea level. 2. Drives to Yosemite National Park and sleeps in Yosemite Valley (4,000 feet) on day 1. 3. Drives to and camps at Tuolumne Meadows (8,650 feet) on day 2. 4. Camps in Tuolumne Meadows for an additional acclimatization on day 3. Gets a little exercise by taking an easy, short hike but avoids strenuous activity. 5. Begins hiking the JMT and camps at Lyell Forks (9,600 feet) on day 4. 6. Continues across Donahue Pass (11,060 feet) and camps at elevations below that. The same hiker might go directly from sea level to Tuolumne Meadows and still incur only a low risk of AMS. If the hiker had previously suffered AMS symptoms and made the trip from sea level to Tuolumne Meadows in a single day, the risk of AMS with would be moderate. These current risk profiles are supported by older data summarized by Gallagher and Hackett [3] as well as the original 2010 guidelines from the Wilderness Medical Society. Here are a few facts of interest:  Given sufficient time, most people (and animals) can acclimate up to about 18,000 feet. Above 18,000 feet, the body cannot adjust to the hypoxia. 

The AMS incidence rate is 20-25% at 8,200 feet.

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The AMS incidence is 40-50% at 13,100 feet.

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When an ascent of 13,100 feet occurs over a number of hours rather than days, AMS rate increases to 90% (e.g., a Whitney day hike from sea level).

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The incidence rate HACE is less than 0.01% at 8,200 feet; 1-2% at 13,100 feet.

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The incidence rate HAPE is less than 0.01% at 8,200 feet; 2-6% at 13,100 feet.

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For trekkers and climbers who ascend 18,000 feet over hours rather than days, the incidence rate of HAPE is 2.5 to 15%. For people with history of HAPE, the risk of recurrence is 60% if they ascend 14,000 feet in 2 days. If untreated, mortality is 50%. [25]

How is AMS recognized? High-altitude illnesses may be difficult to diagnose. The severity of AMS symptoms varies widely and symptoms may be confused with those from other causes, such as severe dehydration, low blood sugar (hypoglycemia), low sodium levels (hyponatremia) or pneumonia. There is not a dependable objective measure to confirm an AMS diagnosis on the trail. For example, measuring the blood’s oxygen saturation with an oximeter is not a reliable test.4 The preferred screening tool for AMS (but not HACE or HAPE) is the Lake Louise Score (LLS) for the diagnosis of Acute Mountain Sickness (AMS) [4, 18]5. The LLS is a self-diagnostic tool that asks questions about five symptoms: headache, gastrointestinal symptoms, fatigue/weakness, dizziness/lightheadedness and difficulty sleeping. Each symptom is assigned a score of 0-3. The total score of all the symptoms can be used to assess if one is suffering from AMS. A combined score of 3-5 indicates mild AMS, while a score of 6 or above indicates a more severe highaltitude illness. The LLS questionnaire is available online: It’s a good idea to include a copy in a first aid kit or scan it into a device (smart phone, tablet) for reference if symptoms develop. The key to good decision-making is to identify symptoms that are being experienced. If a hiker is short of breath with physical exertion, needs frequent breaks, has no energy and cannot keep up with others in the party, there is a problem. It is time to STOP and assess the symptoms.

What can be done to prepare? Take the time to acclimatize! One recent study shows that the vast majority of recreational hikers do not take time to acclimatize [7]. Hikers who have experienced AMS, HACE or HAPE in the past should consult with their healthcare provider as acclimatization strategies may include the use of prescription medications. The last section of this guideline includes recommendations for how to acclimatize.

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Some informal sources discuss the use of oximeters but practitioners of wilderness medicine report oximeter data is unreliable and a poor indicator of the presence of elevation sickness. 5 The LLS is a five question tool that has been taken from the Lake Louise Acute Mountain Sickness Scoring System [18] that was developed in 1991 during the International Hypoxia Symposium held at (of all places) Lake Louise in Alberta Canada.

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What is the best way to acclimatize? For elevations less than 18,000 feet, most people can adjust to hypoxia. There are two ways to adapt: 1) Spend time at progressively higher elevations so that that the body’s ordinary physiological processes can adjust to the reduced oxygen content 2) Take medications that assist the body’s acclimation process. Various drug therapies are discussed in the Wilderness Medical Society’s latest guidelines [5], Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update.6 Discuss these guidelines with a healthcare provider and consider prophylactic therapies to decrease the risks of developing an altitude related illness. PLEASE do not self-medicate with someone else’s prescriptions. The Altitude Illness article from the Centers for Disease Control Yellow Book provides similar, less technical, advice to travelers bound for high altitude destinations in the altitude illness article and describes drug therapies [9]: Below are a few basic guidelines for acclimatizing. The list is based on guidelines from Princeton’s Outdoor Action Site, which has been modified and amended with information that may be relevant to JMT hikers [6]. 

Do not fly or drive to high altitude. Start below 10,000 feet and walk up. All the JMT starts are below 10,000 feet. It’s the first day elevation that is difficult to manage, depending on the entry point.

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If you do fly or drive to 10,000 feet, do not overexert yourself or move higher for the first 24 hours. Plan two or three days at elevation before starting the JMT, doing day hikes from Yosemite, Mammoth or around Mt. Whitney.

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If you go above 10,000 feet, only increase your altitude by 1,000-1,500 feet per day. For every 3,000 feet of total elevation gain, take a rest day. i.e. if you sleep above 13,000 feet, take an extra rest day. The extra night of sleep at this altitude allows for a slower ascent profile [5] and a supportive environment for acclimatization.

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Ascent rates may be calculated as an average ascent over several days. “Using rest days in this manner can ensure that, even though a given ascent may exceed the published recommendations for gain in sleeping elevation, the overall ascent rate may remain slow enough to ensure a safe trip” [5]

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"Climb high and sleep low." You can climb more than 1,000 feet in a day as long as you come back down and sleep at a lower altitude. On the JMT, where the passes are high, plan to sleep as low as you can after summiting a pass.

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At the time this revision was prepared, the 2014 WMS guidelines were only available to subscribers of the Wilderness & Environmental Medicine Journal or through purchase (http://www.wemjournal.org/article/S10806032%2814%2900257-9/abstract).

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If you begin to show symptoms of moderate altitude illness, do not go higher until symptoms decrease. “Don't go up until symptoms go down". Build some flexibility into your plan so you can take an unexpected rest day.

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If symptoms increase, go down, down, down! This may involve backtracking on some parts of the JMT, where continuing to advance will necessitate more elevation gain even after clearing the next pass. Make sure your maps have enough detail to show exit routes off the trail.

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Keep in mind that different people will acclimatize at different rates. Make sure all of your party is properly acclimatized before going higher. The unspoken mountain rule is you go only as fast as the slowest member of the group. Discuss ahead of time what you will do if someone in your party has to take an extra rest day or go back. Do not leave a person alone who is experiencing symptoms of AMS. Will you all stay together? Will you split up into smaller groups? Do you have enough redundant supplies?

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Stay properly hydrated. Acclimatization is often accompanied by fluid loss so you need to drink a large quantity of caffeine-free fluids to remain properly hydrated.7 Dehydration mimics, and is often difficult to differentiate from, AMS. Remember, however, that even well-hydrated hikers develop AMS.

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Take it easy; do not overexert yourself when you first get to altitude. Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms. If you are taking a rest day because of altitude symptoms, regardless of how long you have been on the trail, move around during the day. Do not stay in your tent sleeping all day.

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Avoid tobacco, alcohol and other depressant drugs including narcotics, barbiturates, tranquilizers, and sleeping pills. These depressants may further decrease the respiratory drive during sleep, resulting in a worsening of the symptoms.

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If the hiker experiences HAPE symptoms, the ascent should be delayed until there is stable oxygenation at rest. For hikers who previously had HAPE, a slow ascent plus the use of nifedipine may be recommended. The 2014 WMS guidelines add that, “No studies have prospectively assessed whether limiting the rate of increase in sleeping elevation prevents HAPE; however, there is a clear relationship between the rate of ascent and disease incidence.” [5]

One of our contributors noted there’s a need for the better evidence that caffeine adversely affects acclimatization. Nonetheless, the conventional wisdom is stick with caffeine free fluids. 7

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Acclimatization FAQ Do I need to acclimatize? If you are ascending above 8,200 feet, you should acclimatize (and some sources suggest you should do so over 6,500 feet). Strategies include being knowledgeable about acclimatization, including the benefits of gradual ascent and prophylactic medications that aid in prevention. This suggests that every JMT hiker should acclimatize unless you know how your body typically reacts to altitude. Your rate of ascent is the key to the success of your acclimatization. Acclimatization is especially important for hikers who are traveling to high altitude for the first time (i.e. with no prior experience at high altitude). They should be particularly careful to follow the recommendation when planning their itinerary. [24] Most people do not acclimatize. Why should I bother? Research by Rozier [7] notes that most people do not bother to acclimatize. The reason to acclimate is that without acclimation you pose a risk to yourself and to others. If I follow the recommended strategies, can I be sure I won’t get an altitude-related illness? Remember that everyone is different. The guidelines provide an approach that can minimize the risks of altitude illness for most, but not all, individuals. Some people may develop problems no matter how well they acclimate. Be alert to the signs and symptoms of AMS, HACE and HAPE and be aware of all of the prevention strategies available. How can I determine if my symptoms are bad enough that I need to descend? Be familiar with the symptoms of AMS/HACE/HAPE and apply common sense. Use the Lake Louise Score for AMS [4, 18] as a tool to help you decide how severe the symptoms are. If you are symptomatic, consider staying at the current altitude an extra day, or descending, depending on the severity of symptoms. If I get AMS, HACE or HAPE, what should I do? Stop ascending, assess your symptoms, revisit the risk categories for AMS and consider the 2014 treatment options as recommended by the WMS. Some hikers with AMS may remain at their current altitude and use non-opiate (non-narcotic) analgesics for headache and antiemetics (anti-nausea medications) for gastrointestinal symptom relief, such as nausea [5]. However, descent is still the best treatment option for AMS and HACE as well as HAPE, however, the new treatment guidelines suggest that individuals with HAPE should try to descend and consider the use of nifedipine, as directed and prescribed by your healthcare provider. Why is a repeat of AMS, HACE or HAPE likely? The data confirms that a previous episode is the best predictor that someone will suffer a high-altitude illness. Some individuals have a predisposition to developing altitude illnesses. The acclimation mechanism is not well understood and remains a challenge to Version 2.1. (4/23/17)

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high-altitude researchers. Remember, the most well-considered acclimatization plan may fail and you may have to abort your sojourn. Can I go over a pass that is higher so long as I sleep at an elevation that is no more that the last place I was acclimated? If you have AMS/HACE symptoms on your ascent of a pass, you should return to a lower altitude and spend at least one more day acclimating. If you continue the journey over the pass, sleeping at the lower or acclimatized altitude helps in your continued adjustment to altitude. If your symptoms worsen with the climb over the pass, you are at risk for getting sicker and perhaps being even more isolated from support teams that may need to be activated to assist in your descent. Critically evaluate your risks before you ascend. How do I tell I am at risk for HAPE or HACE? There is no specific way to know your risk. Consult the risk table in the Wilderness Medical Society Guidelines [5]. The ascent profile will aid you in assessing your risk of developing any altitude illness. Can I continue my hike if I experience shortness of breath while resting in the hope that I will acclimate or should I descend? Every hiker experiences shortness of breath from exertion as they climb mountains. If you remain short of breath after a period of rest, you need to descend. If you develop the classic symptoms of headache, nausea and fatigue, return or proceed to a lower altitude, rehydrate and rest for the remainder of the day. If the symptoms resolve overnight, resume your journey. Use the Lake Louise Score [4, 18] as an objective tool in making the decision to proceed, rest or descend. Do not forget to take that extra day to acclimatize if you are ascending over 1,500 feet daily. Take time to acclimatize. Can I use an oximeter to test if I need to turn back? Leave your pulse oximeter at home. Pulse oximetry readings are not predictors of AMS. If you are short of breath with a fast pulse rate after a period of rest, descend. For further information, consider reading Dr. Luks’ review on the use of pulse oximetry at altitude [14]. Do you become more susceptible to HAPE/HACE as you get older? Every mountain recreationalist is unique in their physiology and each will respond differently to the altitude. If you heed the signs and symptoms of AMS and take the time to acclimatize to the environment, age and its physiologic challenges should not interfere with a mountain sojourn. A pre-hike consultation with a knowledgeable healthcare provider may be beneficial if you have health issues. Of note, people over 50 years-old have a slightly lower risk, while children are just as susceptible as adults. The body’s ability to recover from HAPE and HACE may be more challenging if you are older.

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What is this Altitude Induced Peripheral Edema (AIPE) that people complain of while hiking? AIPE is a common adverse effect of hypoxemia, often noticeable as puffy eyes or swollen hands or feet. It is not dangerous by itself, but is commonly found in people with AMS [15]. If you have AIPE you should assess for any signs of HACE and HAPE and manage appropriately [16]. If my hands, feet or face start to swell, is that a warning sign? While AIPE is common, a few people go on to develop more serious forms of altitude illness. You should be alert to worsening signs. The swelling itself may persist as long as you are at certain altitudes and should return to normal when you descend, eliminating the excess fluid from your body through urine output. Should I head to lower elevations if my hands, feet or face start to swell? Not necessarily. If you do not develop other symptoms of AMS/HAPE/HACE you can stay at high elevations. What can I do to treat AIPE? AIPE is not well studied so there is no standard treatment. Salt restriction may be effective. Note that many backpacking foods like jerky, salted nuts and packaged meals contain large amounts of sodium. Acetazolamide (Diamox) may also be effective. What if I develop vision changes or loss of vision? You may be experiencing High Altitude Retinal Hemorrhage (HARH). Most people with HARH will not know they have it. If your vision changes it will probably resolve on its own, but it may take several months. If you have any loss of vision you should descend. What is the most efficient way to acclimate? The best way to acclimate is to ascend gradually. Medications may help, too—talk to your doctor. Educate yourself by reading and following the guidelines, be aware of, and acknowledge, the messages that your body is sending and realize most hikers will experience AMS symptoms to varying degrees. Check out the recommendations on the Princeton’s Outdoor Action Site. How long does acclimation last? Can I acclimate, take a week off and begin my hike? Our bodies are dynamic systems and, unfortunately, the changes associated with acclimatization are dependent upon the environment where you are residing. Acclimatization occurs over time and when you remove the hypoxia of altitude, your body will accommodate to the lower altitude over minutes and days. Even individuals who live at high altitudes who leave for brief intervals have to re-acclimate to high altitude8.

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One of the contributors noted that there may be some acclimatization benefit for up to 2 weeks. While residual benefit may accelerate acclimatization, it should not replace it.

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Does ibuprofen really help? What about aspirin? What about acetaminophen? Is there any difference? Ibuprofen’s effectiveness in preventing AMS in healthy adults was studied in the White Mountains of California and ibuprofen 600 mg taken 6 hours before ascent “resulted in a 26% decrease in AMS when compared to placebo” [11]. There are ongoing trials to determine if ibuprofen helps with acclimatization. Most recreationalists self-report that the anti-inflammatory effects of ibuprofen help with the headaches and body aches associated with a hike to altitude. Aspirin is a strong anti-inflammatory medication; however its blood thinning properties may add unnecessary risk to the hiker. Acetaminophen helps with pain and fever. Rozier [8] found that among subjects using non-steroidal anti-inflammatory medication, the majority preferred ibuprofen. Does Diamox (acetazolamide) work? Diamox (acetazolamide) remains the gold standard in preventing AMS and HACE. Over the years the prescribing recommendations have changed to lower, and more tolerable, dosing protocols. Medical providers should be aware of the Wilderness Medical Society’s 2014 guidelines as they remain the most up-to-date, evidence-based guidelines available and are respected worldwide. The current recommendation for adults in the prevention of AMS/HACE is 125 mg twice daily and should not be confused with the treatment dose of 250 mg twice daily for those with AMS. Diamox is extremely beneficial when there is a requirement to ascend to altitude rapidly, e.g., mountain rescues or travel from low to high altitudes (McMurdo to South Pole Station, Antarctica). Does Diamox (acetazolamide) have side effects I should worry about? Acetazolamide is a powerful medication and you need to discuss its use with the healthcare provider who prescribes it. If you have an allergy to sulfa-based medications, you may develop an allergic-like reaction with acetazolamide. Pay heed to the warnings on the prescription inserts from the pharmacy. DO NOT borrow or share this medication as there are many interactions that can occur and side effects that need to be considered in its application. Acetazolamide helps to prevent the development of AMS/HACE but most individuals who have used it complain about the headache and nausea that can occur, as well as tingling in the extremities. Acetazolamide (a carbonic anhydrase inhibitor) makes beer and carbonated beverages taste “bad” and few people want to take it as they begin their mountain vacations. It remains the drug of choice for acclimatization and is very beneficial in the transition to altitude. The guidelines suggest that the newer, lower doses are better tolerated. Do iron supplements help boost the blood’s ability to absorb oxygen? Do they make a difference? The hemoglobin molecule that binds to oxygen is derived from iron. Iron is stored in our body and when you are exposed to the low oxygen of higher altitudes, the body is stimulated to build new hemoglobin to carry more oxygen. For some individuals, the use of iron supplements 6 to 8 weeks before a high-altitude adventure will increase their body’s iron stores to support the body’s ability to build new hemoglobin and red blood cells, hence enhancing their ability to adapt more quickly to altitude. Studies have yet to

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ascertain the risks and benefits of iron supplementation in the recreational hiker. Your healthcare provider can check your hemoglobin and iron storing abilities. Is ginkgo biloba effective in preventing altitude illness? Over the last several years, there has been a plethora of research done on various medications, vitamins, minerals, naturally occurring substances, antioxidants, nutritional supplements and other modalities, including ginkgo biloba, with conflicting results [17]. The Wilderness Medical Society’s new guidelines [5] reflect the most current evidencebased applications for these. Bottom line, look to the research for your answers. Is there an altitude gene? Unfortunately, at this time, there is no known “altitude gene”. Many genes have been investigated in their role in illnesses caused by altitude. Many of the latest studies have focused on the interactions between hypoxia and genomes with a focus on genetic variations that are seen in high altitude illnesses and associations of population and familial susceptibility. If I’m having trouble sleeping and other mild symptoms, it OK to take a sedative to see if I’m better in the morning and can continue my hike? Sleeplessness is a common problem with adjustment to altitude. Individuals respond uniquely to sleeping aids and someone in your party should know you are using them. Confusion and delirium are symptoms of HACE as well as prolonged effects of sleeping pills. Sleeping aides should be avoided if you have symptoms of HACE or HAPE. Is there a “go to” reference that I can show my doctor, who doesn’t have any special experience with altitude illness? Yes, there are two:  The CDC article on Altitude Illness, by Peter Hackett and David Shlim [9]  Wilderness Medical Society Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update. [5] Note: At the time this version was prepared, the 2014 WMS guidelines were only available to subscribers of the Wilderness & Environmental Medicine Journal or through purchase. However the 2010 WMS guideline is freely available. I’m just in my 20s, do I have to really worry about AMS? Yes! Absolutely! AMS occurs more often in the “young” and “fit” as you frequently “push the limits” of physical endurance beyond what your body can adapt. In the austere, high altitude environment, your 20 year-old colleagues are ignoring the subtle, early signs of AMS and HAPE and, unfortunately, many have succumbed. In the medical world, AMS became a clinical entity in 1960 when young men like Charles Houston, MD starting climbing mountains and realized the clinical significance of going “too high”, “too fast”. The current evidence-based guidelines for climbers and hikers began with his anecdotal notes. Use them.

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Does drinking coffee affect acclimatization? Caffeine in any form (coffee, tea, hot chocolate, Red Bull™, etc.) is a diuretic and diuretics may challenge your ability to stay hydrated during your high altitude adventure. Severe dehydration symptoms are frequently confused with AMS (headache, nausea, fatigue) and should be avoided at all costs. If an individual has been on a stable dose of caffeine for many weeks, there is no need to wean off coffee. Do not suddenly discontinue your accustomed dose of caffeine or the caffeine-withdrawal headache could be misinterpreted. Forced hydration may cause electrolyte loss. Adequate hydration can be supported with the use of integrated hydration backpack systems or frequent hydration stops, and monitored with clear and copious amounts of urine [12]. Is the Lake Louise Score for the self-diagnosis of AMS worth the paper it’s printed on? The Lake Louise Score [4, 18] is an objective tool that is worth its weight in gold. The 5 questions screen for the presence and severity of AMS. The self-report score does not measure HACE or HAPE, however, a high score should alert the hiker to the risk of developing such. The only caveat is that you have to be honest with your answers and you need to take the recommendations to heart. Use the tool and become familiar with it. The WMS recommends not increasing the gain in sleeping elevation by more than 1640 feet (500 m) in a day and including a rest day every 3-4 days. Is that overly cautious? There can be no margin of error in the simple “push” to altitude. One miscalculated ascent can be deadly, not only to the individual, but to the whole team as there are limited resources for rescue operations at high altitudes. For the recreationalist seeking higher ground, the WMS 2014 guidelines are the most current recommendation [5]. You should be prepared to descend when AMS symptoms present and not place others in harm’s way to rescue you. Always err on the side of caution. How should I apply the “hike high/sleep low philosophy?” Is there any reason to limit elevation gain during the day so long as I descend? Luks has published a review of the literature for ascent rates and rest day recommendations [13]. According to Luks, “A prudent way to mitigate the risk associated with this situation would be to have a rest day before and/or after the large increase in sleeping elevation”. The general consensus for ascent over 8,200 feet limits altitude increases for sleeping to 1,000 – 1,500 feet (if the terrain allows) and for the use of a rest day every 3 to 4 days. If anyone in the party has AMS symptoms, descend, rest and re-evaluate. What should I do if I experience AMS symptoms? If you experience AMS symptoms follow these principles: 

Listen and acknowledge what your body is telling you.



Don't go up until symptoms go down.



If symptoms increase, go down, down, down!

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

Stay properly hydrated.



Take it easy; do not overexert yourself.

What should I do if I develop HACE or HAPE symptoms? If you develop HACE or HAPE symptoms, engage the help of your fellow hikers and make a plan for descent. If you are incapacitated or cannot descend, activate a plan for extrication and rescue.

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An example JMT plan with acclimatization In order to understand how acclimatization might influence planned for a JMT hike, we created a sample plan using the following criteria:  Full acclimatization at 8,000 feet before the hike begins  No overnight with more than 1,000 feet elevation gain since the previous camp  Provides time for day hikes at higher elevations and camping at lower elevations Table 2: JMT Plan adjusted for acclimatization Waypoint, descriptions and elevation from Wenk’s Spreadsheet [10] Day Elev Change

Short Name Trail Start

Description Happy Isles

Cam p start

Zero day

Day 1

Elevation (feet) 4,035

Day Miles 0.0

Day start elevation 4,035

Day Max

+Chang e 0.0

-Change 0.0

Ttl overnig ht change 0.0

Resupply

Max Elevation gain 0.0

Max elevation loss 0.0

Y/N

Days

Miles

-

-

-

2

24.0

Regular stop over on the main route Short day mileage to permit further acclimatization before ascent. Add 10-mile Day hike to Ireland Lake @ 10.7K to 'hike high; sleep low" Note: HACE/HAPE symptoms possible on day 3. Short mileage day to permit further acclimatization. Add 6mi day hike to Donohue Pass vista @ 11.2K to "hike high; sleep low"

large opening in dense forest alongside Sunrise Creek; other options further upstream Tuolumne High Sierra Camp junction

camp

1

8,540

10.3

4,035

4,565

(60)

4,505

4,505

-

camp

2

8,680

13.7

8,540

715

(1,625)

140

1,160

-

Evelyn Lake Junction

Evelyn Lake Junction

camp

3

8,900

5.5

8,680

230

-

220

220

-

-

-

Lyell / Mclure Bridge

flat area among hemlocks and lodgepole pines to the east of the bridge crossing

camp

4

9,680

4.0

8,900

710

(20)

780

800

-

-

-

Sunrise Creek

TLM

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yes

Notes Assume 2 previous overnights at 8K. E.g. Tuolumne backpacker’s camp, or White Wolf backpacker's camp. 4.5K elevation change is OK since pre-hike overnights at 8K

-

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Day Elev Change

Short Name

Description

Cam p

Zero day

Day

Elevation (feet)

Day Max

Day Miles

Day start elevation

+Chang e

-Change

Ttl overnig ht change

Resupply

Max Elevation gain

Max elevation loss

small sites along the southern shore of Garnet Lake; small flat sections on an otherwise steep slope; excellent views Reds Meadow Junction

camp

5

9,700

12.0

9,680

2,260

(2,210)

20

1,380

(40)

camp

6

7,715

13.2

9,700

1,090

(3,475)

(1,985)

-

(2,225)

Deer Creek

large site just to the north of the Deer Creek crossing in open lodgepole forest; other sites nearby

camp

7

9,100

6.0

7,715

585

(125)

1,385

1,505

Cascade Creek

sites along in trees to edge of small marsh; just south of bridge crossing small site with beautiful views and junipers on descent to Bear Creek

camp

8

9,760

13.9

9,100

2,065

(1,405)

660

camp

9

9,520

14.2

9,760

2,575

(3,612)

JMT N cutoff

camp

10

8,400

14.3

9,520

2,040

several small to large sized sites towards the eastern end of McClure Meadow, beautiful views to Mt. Darwin and the Hermit

camp

12

9,640

11.0

8,400

Starr Camp; lots of good sites among young lodgepole pines to the south of the trail; beautiful views of Languille

camp

13

10,320

13.9

9,640

Garnet Lake

Reds Meadow

Bear Creek

JMT McClure Meadow

Starr Camp

rest

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Y/N

Days

Miles

-

-

4

34.7

-

-

-

1,250

-

-

-

(240)

1,135

(2,117)

-

-

(3,120)

(1,120)

1,370

(1,120)

4

48.4

1,880

(40)

1,240

1,240

(620)

-

-

2,250

(1,660)

680

2,340

-

-

-

yes

yes

Notes Note: HACE/HAPE symptoms possible on day 4. Small elevation loss at Garnet Lake since camp at Lyell forks. Note: Likelihood of HACE/HAPE symptoms diminish on Day 5. Steep descent. No acclimatization risks. Tomorrow 1/2 zero day. Take zero miles in morning. Short mileage day to acclimate to 1.3K ascend from previous night. Avoid additional ascent towards Duck Pass. Note: 1.3K elevation gain. Be alert to symptoms Cascade valley is low point closest to Silver Pass. Only 660 in elevation gain. Hike high, sleep low" day. Cross Silver Pass. Bear Creek is nearest low point. Note: Assumes the VVR is skipped. MTR zero day and resupply. Risky 1.2K elevation gain needed to prepare for Muir Pass. May need to descend back to Evolution Creek to lose 400 feet. If symptoms develop backtrack to Goddard Canyon trail junction for overnight. Note: If successful, the next 5 nights are low risk. Highest campsite to date. Requires comfortable overnight at McClure Meadow (i.e. north of Muir Pass). If symptoms develop press

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Day Elev Change

Cam p

Zero day

Day Miles

Day start elevation

+Chang e

-Change

Resupply

Max Elevation gain

Max elevation loss

Short Name

Description Peak, the Black Giant and Le Conte Canyon

Palisade Creek

several medium-size sandy sites to edge of slabs at the lower Palisade Lake outlet; beautiful views to the west and to the middle Palisades small sites among whitebark pines at and below Lake Marjorie outlet Arrowhead Lake (CAMP 10.10) Independence

camp

14

10,630

14.2

10,320

2,610

(1,450)

310

310

(2,260)

-

-

Modest elevation gain. Low risk overnight.

camp

15

11,130

11.5

10,630

2,330

(2,060)

500

1,470

(590)

-

-

Modest elevation gain. Low risk overnight.

camp

16

10,300

13.4

11,130

2,688

(3,638)

(830)

1,000

(2,638)

-

-

17

3,933

13.3

10,300

1,485

(8,102)

(6,367)

1,660

(6,367)

6

70.2

large site in dry lodgepole forest at edge of Vidette Meadow; views to East Vidette

camp

19

9,560

9.6

3,933

7,239

(1,612)

5,627

6,809

-

-

-

large site under open lodgepole pines at Tyndall Creek trail junction

camp

20

10,880

12.0

9,560

3,155

(2,220)

1,320

3,540

-

-

-

Descending. Low risk overnight Full day. Two Pass hike (Glenn + Kearsarge). Descend to Independence for resupply. Low risk overnight. Take zero-day in Independence. Note: Add 14-miles for hiking over Kearsarge Pass to Independence Possible Risk. After 2 nights in Independence (~4K), there may be some reversion in the acclimation process. Some additional acclimation may be required. As a conservative approach, consider spending the zero-day at Gray's Meadow Campground (~6K). Riskiest day of trip. Cross Forrester Pass at 13.1K and camp with 1.3K elevation gain. If symptoms occur, there is no good option. Best option appears to be exit over Sheppard's Pass at 12K where the elevation drops quickly after a 3.5 mi hike.

Lake Marjorie

Arrowhead Lake Independen ce

Vidette Meadow

Tyndall Creek

camp

rest

Day

Elevation (feet)

Day Max Ttl overnig ht change

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Y/N

yes

Days

Notes on to Little Pete Meadow

Miles

21

Day Elev Change

Short Name Guitar Lake

Exit

Description many exposed, sandy sites among slabs and boulders on bluffs above the west end of Guitar Lake; beautiful views to the Kaweahs and Mt. Whitney; you must leave the trail to find these sites Whitney Portal

Cam p camp

camp

Zero day

Day 21

Elevation (feet) 11,550

22

8,330

Day Max

Day Miles 11.3

Day start elevation 10,880

+Chang e 2,023

-Change (1,353)

Ttl overnig ht change 670

15.3

11,550

3,025

(6,210)

(3,220)

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Max Elevation gain 670

Max elevation loss (480)

2,955

(3,220)

Resupply

Y/N

yes

Days

Miles

-

-

5

41.2

Notes Modest elevation gain. Low risk overnight.

Summit Whitney holds AMS risk, but the 3K elevation gain is a day hike and should not evoke HAPE/HACE unless the body is operating on the edge. If symptoms occur there's a rapid descent towards Whitney Portal.

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Summary “An Unofficial Acclimatization Guideline for JMT Hikers” provides basic information about altitude illnesses. AMS, HAPE, HACE and other conditions may be experienced at the higher elevations on the John Muir Trail and around the Sierra. Hikers who prepare for acclimatization, recognize the signs and symptoms of altitude illnesses and understand how to react are more likely to enjoy their time in the mountains safely.

About the authors Leslie H. Rozier, DNP, APRN A nurse practitioner who has spent almost 4 decades caring for individuals worldwide who failed to recognize that acclimatization is a crucial step in the journey to an enjoyable, successful, high-altitude sojourn. Inga Aksamit, RN-BC, MBA A nurse, outdoor enthusiast, hiker, backpacker and writer who is passionate about exploring mountains safely and encouraging others to push their limits. She’s done the John Muir Trail, High Sierra Trail, Chilkoot Trail, many trails in the Tahoe Sierra and has paddled 450 miles of the Yukon River in a canoe. Kenny Meyer, hiker Retired software engineer who was unable continue his JMT hike in 2014 because he experienced HAPE symptoms after camping at Lyell Forks (9,650 feet elevation). Special thanks to Andrew Luks, MD for his professional and graceful recommendations, Paul Papanek, MD, MPH, FACOEM for his extremely helpful suggestions and Ned Tibbits for his encouragement to dig deeper into the topic. We also want to express our deep appreciation for the high altitude researchers who have shared their experience and expertise so that we may safely enjoy recreational hiking at high altitude.

References [1]

Altitude.org: http://www.altitude.org/altitude_sickness.php

[2]

removed

[3]

Gallagher, S.A., & Hackett, P.H. (2004). High-altitude illness. Emergency Medicine Clinics of North America, 22, 329-355.

[4]

Lake Louise Score (LLS) Self-Report Questionnaire. http://unofficialacclimatizationguideline.blogspot.com/p/lake-louise.html

[5]

Luks, A. M., McIntosh, S. E., Grissom, C. K., Auerbach, P. S., Rodway, G. W., Schoene, R. B., Zafren, K. & Hackett, P. H. (2014) Wilderness Medical Society practice guidelines for the prevention and treatment of acute altitude illness: 2014 update. Wilderness and Environmental Medicine, 25(S4-S14).

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[6]

Curtis, R. Outdoor Action Guide to High Altitude: Acclimatization and Illnesses. http://www.princeton.edu/~oa/safety/altitude.shtml

[7]

Rozier, L. H. (2013). Acclimatization Practices of High-Altitude Recreationalists, Wilderness & Environmental Medicine, 24(3), 291–292.

[8]

Rozier, Leslie. From a Sep 18 ’14 email to Kenny Meyer.

[9]

Hackett P.H. & Shlim P.R. (2013). Altitude Illness. US Centers for Disease Control and Prevention. http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travelconsultation/altitude-illness

[10]

Wenk E. (2014). John Muir Trail: The essential guide to hiking American’s most famous trail. 5th ed. Wilderness Press.

[11]

Lipman, G., Kanaan, N., Holck, P., Constance, B. & Gertsche, J. (2012). Ibuprofen prevents altitude illness: A randomized controlled trial for prevention of altitude illness with nonsteroidal anti-inflammatories. Annals of Emergency Medicine, 59(6), 484-490.

[12]

Rozier, L. (1998). The hydration status of backpackers at high altitude. International Journal of Circumpolar Health. Supplement 57:742-745.

[13]

Luks, A. (2012). Clinician’s Corner: What do we know about safe ascent rates at high altitude? High Altitude Medicine & Biology, 13(2):147-152.

[14]

Luks, A. Swenson, E. (2011). Pulse Oximetry at high altitude. High Altitude Medicine and Biology, 12(2):109-119.

[15]

Rock, P.B. & Mader, T.H. (2002). Additional medical problems in mountain environments. In K.B. Pandoff & R.E. Burr, (Eds.), Medical aspects of harsh environments, Vol 2. Office of the Surgeon General, U.S. Army (pp. 816-818).

[16]

Army Tech Bulletin TB MED 505 (2010). Altitude acclimatization and illness management. Headquarters, Department of the Army. Washington DC.

[17]

Gertsch, J.H., Basnyat, B., Johnson, E.W., Onopa, J. & Holck, P.S. (2004). Randomized, 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(7443).

[18]

Roach, R.C., Bartsch, P., Hackett, P.H., Oelz, O. and the Lake Louise AMS Scoring Consensus Committee (1991). The Lake Louise acute mountain sickness scoring system. In J.R. Sutton, C.S. Houston & G. Coates (Eds.), Hypoxia and Molecular Medicine. Burlington, Vermont: Queen City Press. (http://dx.doi.org/10.1016/j.wem.2014.06.017).

[19]

U.S. Standard Atmosphere, 1976. National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration, United States Air Force. Washington DC, 1976.

[20]

Severinghaus, J. W. (1979). Simple, accurate equations for human blood O2 dissociation computations. J Appl Physiol. 46(3): 599-602.

[21]

Houston, C., Harris, D., Zeman, E.J. (2005). Going Higher, Oxygen, Man, and Mountains. Mountaineers Books. Seattle, WA.

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[22]

Pittman, R. N. (2011). Regulation of Tissue Oxygenation. San Rafael (CA): Morgan & Claypool Life Sciences; San Rafael, CA.

[23]

From Critical Care Medicine Tutorials. “All about Oxyen. http://www.ccmtutorials.com/rs/oxygen/index.htm

[24]

Luks, A. (2012). Clinician’s Corner: What Do We Know About Safe Ascent Rates at High Altitude? High Altitude Medicine & Biology. 13(3).

[25]

Bartsch, P., Swenson, E. (2013). Acute High-Altitude Illnesses. New England Journal of Medicine. (368) 2294-302.

[26]

Rock, P.B. & Mader, T.H. (2002). Additional medical problems in mountain environments. In K.B. Pandoff & R.E. Burr, (Eds.), Medical aspects of harsh environments, Vol 2. Office of the Surgeon General, U.S. Army (pp. 824-827).

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Appendix I.

Data Tables

The following tables include the data used for the figures in the document Source Data for Figure 1, “Oxygen content of the air drops rapidly with elevation”

Elevation (Feet) 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000 15,000

Elevation (Meters) 305 610 914 1,219 1,524 1,829 2,134 2,438 2,743 3,048 3,353 3,658 3,962 4,267 4,572

Barometric Barometric Pressure Pressure (mmHg) (inHg) 760 29.9 734 28.9 709 27.9 685 27.0 662 26.1 639 25.2 617 24.3 595 23.4 574 22.6 554 21.8 534 21.0 514 20.2 496 19.5 478 18.8 460 18.1 443 17.4

PaO2 (mm Hg) 158.84 153.41 148.18 143.17 138.36 133.55 128.95 124.36 119.97 115.79 111.61 107.43 103.66 99.90 96.14 92.59

Notes:  Data derived from “U.S. Standard Atmosphere, 1976.” [19]  Round off errors due to TORR-mmHg conversion (1 Torr = 0.999999... mmHg)  O2 fractional volume = 0.209/mmHg [19]

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Source data for Figure 2, “Blood hemoglobin releases O2 when the saturation drops”

PO2 (mmHg) 10.3 19.2 22.8 26.6 36.9 44.5 57.8 74.2 99.6

O2 Saturation (%) 10 30 40 50 70 80 90 95 97.5

Notes:  Values based on the Severinghaus equation [20]: SO2 = (23,400 * (pO23 + 150 * pO2)-1 + 1)-1  Value verified with two online Oxygen Saturation calculators: - http://www-users.med.cornell.edu/~spon/picu/calc/o2satcal.htm - http://www.altitude.org/oxygen_levels.php

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