Water Intoxication Case in Hiker

While emphasis is often placed on keeping athletes and outdoor enthusiasts properly hydrated, too much water can be just as dangerous. Exercise-associated hyponatremia (EAH), a form of water intoxication, results in an extreme, and potentially fatal, sodium imbalance.

In the latest issue of Wilderness & Environmental Medicine, investigators detail the case of a hiker who died as an illustration of the potential danger of endurance exercise and excessive water intake lowering serum sodium to a dangerous level. There have been several deaths from EAH associated with various sports. This is one of few reported fatalities due to EAH in a wilderness setting.

The study details the death of a 47-year-old female hiker who passed out after a 10 km hike on the South Kaibab Trail in Grand Canyon National Park in 2008. Over a five-hour period, the woman consumed a large amount of water but ate very little food. She collapsed approximately an hour after finishing the hike. Despite the efforts of emergency medical personnel, the patient was pronounced dead 19 hours later from cerebral edema brought on by water intoxication.

As outdoor endurance recreation grows in popularity, so does the risk of EAH. Early symptoms of EAH often mimic dehydration and include nausea, vomiting, malaise, and headache. If left untreated, the condition can lead to an altered mental status, seizures, and death. Unfortunately, many practitioners have difficulty recognizing the condition and treating it appropriately.

“EAH results from overhydration, and avoiding additional fluid overload is critically important in treatment,” explained co-investigator Martin D. Hoffman, MD. “Because dehydration is often a reflex diagnosis for a symptomatic exerciser in a hot environment, the usual treatment of oral or IV isotonic or hypotonic fluids needs to be resisted if there is a strong likelihood that the underlying condition is EAH.”

What can we use from this in teaching undergraduate A&P?

• When discussing fluid/electrolyte balance, we can introduce the concepts of water intoxication and EAH


• This particular case can be discussed as an example of water intoxication


• This particular case could be adapted into a case-study activity in your course—or a case-study problem on a test.


• The fact that early symptoms of EAH mimic dehydration, creates a clinical issue.  Class discussions regarding this—including suggested solutions from the research article—could be fruitful in increasing the understanding of basic principles of fluid/electrolyte balance in the body—as well as critical thinking skills.


• This is a good example of practical applications of fluid/electrolyte balance, thus answering the common question, "why do we have to learn all this?!"


• Everybody should know this, right?

Quick points about water intoxication (EAH)

EAH symptoms

• Impaired exercise performance
• Nausea and vomiting
• Headache
• Altered level of consciousness
• Seizure (convulsion)
• Muscle cell breakdown (rhabdomyolysis) with the development of acute kidney failure

NOT symptoms of neither EAH nor dehydration

• Dizziness and fainting
• Muscle cramping
• Wheezy breathing

Risk factors of EAH

• Overdrinking water, sports drinks, and other hypotonic beverages
• Weight gain during exercise
• Exercise duration of more than 4 hours
• Event inexperience or inadequate training
• Slow performance pace
• High or low body mass index
• Readily available fluids

Want to know more?

Hiker Fatality From Severe Hyponatremia in Grand Canyon National Park

• Thomas M. Myers, MD, and Martin D. Hoffman, MD. Wilderness & Environmental Medicine, Volume 26, Issue 3 (September 2015) DOI: http://dx.doi.org/10.1016/j.wem.2015.03.001
• Research article outlining the case, including causes, outcomes, and suggestions for successful diagnosis and treatment of EAH.
• my-ap.us/1h7J3Qy

Seven clear symptoms of Exercise-Associated Hyponatremia

• Timothy Noakes. Human Kinetics. Accessed 28 Sep 2015. 
• Excerpt from the book Waterlogged: The Serious Problem of Overhydration in Endurance Sports (ISBN-13: 9781450424974) Source of the symptoms "quick points" listed above.
• my-ap.us/1h7JeeJ

Guidelines Released for Exercise-Associated Hyponatremia

• Diana Phillips. Medscape Medical News. July 03, 2015
• Summary of recent guidelines published in a statement developed at this year's Third International Exercise-Associated Hyponatremia Consensus Development Conference. Source of the risk factors in the "quick points" listed above.
• my-ap.us/1P41yTN

Some text adapted from an Elsevier press release
Top photo: Sanja Gjeero
Bottom photo: Sara Hammeraback

A Brain-Lymphatic Connection

Existing dogma in neuroscience states that the brain does not possess the classical lymphatic drainage system found in other parts of body. However, a recent letter in the journal Nature reports the discovery of lymphatic vessels lining the dural sinuses in mice. These were shown to drain immune cells and cerebrospinal fluid (CSF) into the deep cervical lymph nodes.

Although more work is yet to be done in humans, this discovery will cause neuroscientists to revisit a number of concepts related to CSF and lymphatic drainage, as well as immune functions in the brain.

For example, do these new data truly challenge the notion of immune privilege in the nervous tissue of the central nervous system—or do they apply to the brain as an organ and allow for lymphatic drainage of tissues outside the nervous tissue of the brain?

What can we use from this in teaching undergraduate A&P?

• When discussing CSF drainage, consider mentioning the possibility that filtration of CSF directly into dural sinuses may be augmented by the newly discovered lymphatic drainage.


• If you discuss the dogma of the "immune privilege" of the brain, consider mentioning this possible challenge to the concept. This may trigger a great discussion of whether these newly discovered lymphatic vessels are truly "in the brain."


• If you discuss disorders involving altered immunity, such as multiple sclerosis, consider mentioning this discovery.


• Bringing up this new information may be useful in discussions related to the process of science—how existing concepts are sometimes challenged by new information, for example. Perhaps a discussion of the need for more investigation would stimulate students to think about what future steps can be taken to map out a possible lymphatic network in or around the brain.

Current concept of lymphatic drainage (left) compared to updated version to reflect new data (right).

Want to know more?

Brain Drain | The brain contains lymphatic vessels similar to those found elsewhere in the body, a mouse study shows.

• Ashley P. Taylor, The Scientist, June 1, 2015 (online)
• Plain-English article summarizing the study and its significance.
• my-ap.us/1IezLLF

Structural and functional features of central nervous system lymphatic vessels,

• A. Louveau et al., Nature, June 1, 2015.doi:10.1038/nature14432, 
• The original research article. Includes images and video.
• my-ap.us/1KNFPy6

Missing link found between brain, immune system; major disease implications

• University of Virginia Health System, Science Daily, June 1, 2015
• Illustrated press release describing the research.
• my-ap.us/1HQys2J

Images: DBCLS (top)
Univ Va Health System (bottom)

Another posterior pituitary hormone

A recent paper in the Proceedings of the National Academy of Science shows that that the posterior pituitary (neurohypophysis ) secretes another hormone besides antidiuretic hormone (ADH; vasopressin) and oxytocin (OT).  It is the hormone secretin.

Secretin is already known to be secreted from the intestinal lining, having a variety of effects in regulating stomach and pancreatic function during the digestive process.  New findings indicate, however, that secretin is also secreted by the posterior pituitary.

Neurohypophysial release of secretin is triggered by plasma hyperosmolality—as in dehydration of the body. Secretin then promotes the expression and release of ADH, which in turn promotes water conservation by the kidney.  Secretin also appears to have direct water-conserving effects in the kidney as well.

Want to know more?

Secretin as a neurohypophysial factor regulating body water homeostasis
Jessica Y. S. Chu, et al. 
Proceedings of the National Academy of Science  September 15, 2009 vol. 106 no. 37 15961-15966 
doi: 10.1073/pnas.0903695106
[Abstract of the recent paper.]

Highlights From The Literature
Physiology 2009 24:322-324
doi:10.1152/physiol.00037.2009
[Summary of the significance of this discovery.] 

Click here for a FREE 3D see-through image of the pituitary's location that you can use in your course.