You and a friend are on a long run in the foothills of the Laramie Range in Wyoming. It’s a hot day. Four hours into the run your companion stumbles, slows, staggers, and sits on a log. He says he “feels awful.”
The patient is a 34-year-old male. His chief complaint is “feeling awful.” You are 6 hours into a planned 24 mile trail run at elevations ranging from 6,000-8,000 feet (1,800-2,400 meters).
There is no mechanism of injury. Nothing unusual found on head to toe assessment. No edema, rashes, swelling, or bruises.
12:00 PM (noon)
Level of Responsiveness (LOR)
Heart Rate (HR)
76, strong, regular
Respiratory Rate (RR)
20, easy, regular
Skin Color, Temperature, Moisture (SCTM)
Skin is warm, flushed (seems appropriate amount of sweat for this run). Mucous membranes are pink.
Blood Pressure (BP)
Strong radial pulse
PERRL (Pupils equal, round, responsive to light)
Not taken, skin not warm to touch
The patient complains of feeling dizzy, shaky, “weird,” anxious, nauseous and having a dull headache.
They deny allergies.
Ibuprofen 800mg at 0500, 400mg at 1000
The patient has been drinking water. He drained his 2L hydration backpack twice today. He has not urinated since the start of the run. He has eaten two energy bars (200mg sodium each) and one salt tablet (215 mg sodium). He denies thirst.
The patient has been trail running for 6 hours (18 miles). It’s hotter than expected under a blazing sun. The patient has a visor sun shade, sun glasses, light synthetic clothing and a very light pack.
What is your assessment and plan? Take a few minutes to figure out your own assessment and make a plan. Don’t cheat—no reading on without answering this first!
- Rest in the shade.
- Slow water intake.
- Eat more salty energy bars.
- Monitor for improvement. An evacuation decision is premature. We have 4 miles to go and 8 hours of daylight. This location is accessible by ATV or helicopter. We have a good cell signal.
- Interview the patient to assure we have a complete history.
The problem worsens. We are unable to continue.
These signs and symptoms are vague and could be any number of problems; over hydration, fatigue, hypoglycemia, altitude illness, and flu-like illness are at the top of your problem list. The history of water intake suggests over-hydration. Altitude illness is unlikely in this time frame unless the patient has a history of susceptibility to AMS or the altitude is really high (it’s not). The food intake may be low, so he might be hypoglycemic. We can’t rule out heat exhaustion, although the normal mental status suggests that heat stroke is not present. Maybe he’s just getting sick.
Interviewing the patient is a good idea—you might find out more about recent health, food intake, hydration, previous experience on endurance runs, etc.
Regardless, the treatment plan of resting in the shade, slowing water intake, and eating is appropriate for possible heat stress/exhaustion and hypoglycemia/fatigue. Limiting fluid intake until you have a better sense of his hydration status is a good plan.
The Tale Continues…
The interview with the patient reveals that their total water intake since 6:00 a.m. has been five liters. His plan was to start the day with “a full tank.” The patient ate the energy bars and the salt tablet and drank the water to keep his energy level high. He has no concept of the risk of over-hydration. He does have a history of “bonking” in previous multi-hour exercise sessions, which he attributes to not eating and drinking properly.
After an hour of rest with only sips of water, the patient urinates copious clear urine and states he can walk. The patient has not eaten due to nausea. He is A+Ox4 and says he no longer feels weird or shaky—he must have “hit the wall.” The patient reports a dull headache, but the dizziness has resolved. You begin to walk to the trail head. The day remains hot and you both are now very stiff from the hour of inactivity.
The walk to the trailhead is uneventful. The patient sips about 250cc of water en route, urinates copiously once more, and eats another energy bar. He arrives at the trailhead feeling tired and sore; in his words, “wasted.”
We don’t know exactly what was going on here. The patient never saw a physician. He convinced himself he had a touch of the flu. Our suspicion is over-hydration (hyponatremia), the subject of this discussion.
As a reminder, the primary risk factor for exertional hyponatremia (a relative low blood sodium due to dilution) is excess fluid intake. A common scenario is intake greater than 1-1.5 liters an hour for 4 hours or more. There may be influence from inappropriate anti-diuretic hormone levels causing fluid retention. NSAID (ibuprofen) use impacts the kidneys and is a concern, but this risk remains unclear.
We prevent exertional hyponatremia with judicious hydration. The mantras of “hydrate or die” or “drink to stay ahead of thirst” may get you into trouble. Thirst is a good indicator of fluid need, so “drink according to thirst.” Sodium supplements during exercise have not been shown to prevent exertional hyponatremia in the face of over-hydration.
Experience is critical. We must understand our individual fluid needs when we exercise in different environmental conditions.
Signs and symptoms of exertional hyponatremia vary among individuals and depend on the patient’s hydration and sodium levels. The patient may appear to have heat exhaustion: headache, weakness, fatigue, lightheadedness, muscle cramps, nausea with or without vomiting, sweaty skin, normal core temperature, and normal or slightly elevated pulse and breathing rates.
The field treatment of possible hyponatremia begins with an accurate fluid intake history. If over-hydration is suspected, then slow or stop fluid intake until symptoms resolve. Salty snacks are appropriate, but by themselves will not correct exertional hyponatremia. Have the patient rest in the shade with little or no fluid intake and a gradual intake of salty foods, while the kidneys reestablish a sodium balance. Brisk urine production usually indicates things are progressing in the right direction. Oral electrolyte replacement drinks are low in sodium and high in water, and may not help as much as you anticipate. Patients with neurological signs and symptoms, e.g. altered mental status, should be promptly evacuated.
As a NOLS Instructor since 1973 and a WEMT, volunteer EMT on ambulance and search and rescue squads since the 70s, Tod Schimelpfenig has extensive experience with wilderness risk management. He has used this valuable experience to conduct safety reviews as well as serve as the NOLS Risk Management Director for eight years, the NOLS Rocky Mountain Director for six years, and three years on the board of directors of the Wilderness Medical Society, where he received the WMS Warren Bowman Award for lifetime contribution to the field of wilderness medicine. Tod is the founder of the Wilderness Risk Manager’s Committee, has spoken at numerous conferences on pre-hospital and wilderness medicine, including the Australian National Conference on Risk Management in Outdoor Recreation, and has taught wilderness medicine around the world. He has written numerous articles on educational program, risk management and wilderness medicine topics, and currently reviews articles for the Journal of Wilderness and Environmental Medicine. Additionally, he is the author of NOLS Wilderness Medicine and co-author of Risk Management for Outdoor Leaders, as well as multiple articles regarding wilderness medicine. Tod is the retired curriculum director for NOLS Wilderness Medicine and is an active wilderness medicine instructor