Wilderness Medicine

Educational Objectives

The goal of this program is to improve management of conditions related to environmental exposure. After hearing and assimilating this program, the clinician will be better able to:

1. Differentiate hypervolemic vs hypovolemic exercise-associated hyponatremia.
2. Manage frostbite through optimal use of thrombolytic agents.

Summary

Drowning: is the process of experiencing respiratory impairment as a result of submersion or immersion in a liquid medium; it is divided into 3 categories, ie, drowning with fatality, drowning that is nonfatal with morbidity, and drowning that is nonfatal without morbidity; drowning causes ≈360,000 deaths annually; most drowning cases involve pediatric patients, with a median age of 18 yr in one study, 50% being children aged 1 to 4 yr; ≈30% of patients suffered cardiac arrest, with a rate of return of spontaneous circulation of 37%

Management: always suspect hypothermia in drowning victims; maintain cervical spine precautions depending on the mechanism; prioritize airway, circulation, and breathing during cardiopulmonary resuscitation (CPR); oxygenation is the most important factor; the Heimlich maneuver is not recommended; serial radiographic evaluation is helpful; the average amount of fluid ingested by a patient who has drowned is 1 to 3 mL/kg; studies on dogs showed significant fluid volumes (30-40 mL/kg) were needed to cause electrolyte abnormalities; laboratory tests for patients with suspected drowning may have limited utility; use of antibiotics should be based on clinical judgment and signs of infection; a 24-hr pneumonitis may occur without microbial involvement; there is no empiric role for steroids; the Wilderness Medical Society’s guidelines recommend a 4-to-6-hr period of observation; patients who do not fully recover or have abnormal vital signs should be admitted

Exercise-associated hyponatremia: the hypervolemic form is more common than the hypovolemic form; patients at increased risk for the hypovolemic form include those on long-term diuretics and older men; hypervolemic hyponatremia occurs when individuals consume excessive fluids during endurance events; hypovolemic hyponatremia occurs when individuals do not consume enough fluids during an event and experience vomiting or other fluid losses; the incidence of exercise-associated hyponatremia (<24 hr) is 30% to 51%; ≈1% of individuals have symptoms, most commonly marathon runners; assess for mental status changes, including confusion, delirium, seizures, or coma; signs and symptoms overlap with heat exhaustion and heat stroke; for patients with symptoms or collapse during exercise, the first step is to assess their mental status; consider the history of fluid intake and measure core body temperature (>40°C could be suggestive of heat stroke); for mild heat exhaustion, patients can rehydrate with fluids; in mild exercise-induced hyponatremia, limiting free water and hypotonic fluids is recommended; hyponatremia is managed with oral or intravenous (IV) boluses of 100 mL of hypertonic saline every 10 min (≤3 doses); most patients show neurologic improvement with 2 doses; oral hypertonic fluids may be administered; for mild exercise-associated hypernatremia, fluid restriction and salty snacks are helpful; antiemetics may be given

Heat stress, exhaustion, and stroke: the 2 main models are classical and exercise-induced; the classical model involves prolonged exposure to a hot environment, often in confined spaces; the exercise-induced model involves heat stress during physical activity; heat illness ranges from mild conditions like heat edema and prickly heat to more severe forms, eg, heat stress, exhaustion, and stroke; untreated heat stress can lead to heat stroke, which carries a high risk for mortality; symptoms of heat stress include headache, nausea, vomiting, and malaise; orthostatic hypotension is common; temperature is <104°F; organ dysfunction may occur with heat injury; patients with heat exhaustion should be treated aggressively, eg, IV hydration, antiemetics, and observation for several hours

Heat stroke: patients typically display signs of central nervous system involvement in addition to a temperature >40°C/104°F; the most common first symptom is ataxia; treatment involves removal from the heat source and cooling; hypotension may occur; vasoconstrictors should be used cautiously as they can impair the body's ability to dissipate heat; consider inotropic agents; monitoring includes core temperature (rectal, bladder, esophageal); rectal temperature can provide a quick assessment of core temperature upon presentation; the best measure is esophageal temperature; after initiating cooling, rectal temperature may be falsely elevated; focus on achieving a temperature <39°C; noninvasive cooling can be achieved through cold water immersion, wetted ice packs, and cold IV fluids; traditional cold immersion systems used in sports may not be suitable for elderly patients; extracorporeal membrane oxygenation or cardiopulmonary bypass are alternative options; cold water gastric, rectal, bladder, peritoneal, and thoracic lavage are less commonly used

Hypothermia: with cold stress, the patient is conscious, movement may be sluggish, and shivering is present; the patient is alert; mild hypothermia is characterized by consciousness, sluggish or minimal movement, shivering, and alertness; with moderate hypothermia, the patient is conscious, not moving, and may not be shivering; severe or profound hypothermia (<28°C) lead to loss of consciousness; when anesthetizing or paralyzing hypothermic patients, use lower dosages and longer intervals, especially <30°C; ventilate at half the standard rate (7-8 breaths/min); for shockable rhythms below 30°C, administer one shock at maximum power and avoid further shocks until the patient's temperature rises >30°C; avoid vasoactive drugs until the patient's temperature is ≥30°C; from 30°C to 35°C, increase the dosage of vasoactive drugs; delayed or intermittent CPR may be provided; there is no temperature cutoff for CPR; a potassium level >12 mmol/L is a criterion for stopping CPR; patients with hypothermia benefit from slower, more controlled warming; as hypothermic patients warm, they may experience hypotension; gradual warming (≈2°C/hr) allows for closer monitoring and timely intervention for hypotension

Frostbite: traditional management is sufficient for patients with normal perfusion; angiography and Doppler studies can be obtained for patients with signs of decreased perfusion; thrombolysis can be performed to treat perfusion defects; Heard et al (2020) found thrombolytics significantly improved limb and digit salvage rates (70%-80%) compared with traditional methods (7%-10%); the recommended dosage is a 3-mg bolus of tissue-type plasminogen activator (TPA) followed by an infusion, along with starting heparin; additionally, catheter-directed TPA can be used

Lightning strikes: reverse triage — in disaster events, focus on black tags (patients with cardiac and respiratory center stunning) first, as their conditions are often reversible; Cronos paralysis, characterized by transient paralysis of the extremities, can mimic arterial occlusion; it usually resolves within a few hours

Readings

Avellanas Chavala ML, Ayala Gallardo M, Soteras Martínez Í, Subirats Bayego E. Management of accidental hypothermia: a narrative review. Med Intensiva (Engl Ed). 2019;43(9):556-568; Bouchama A, Abuyassin B, Lehe C, et al. Classic and exertional heatstroke. Nat Rev Dis Primers. 2022;8(1):8. doi:10.1038/s41572-021-00334-6; Heard J, Shamrock A, Galet C, Pape KO, Laroia S, Wibbenmeyer L. Thrombolytic use in management of frostbite injuries: eight year retrospective review at a single institution. J Burn Care Res. 2020;41(3):722-726. doi:10.1093/jbcr/iraa028; Hew-Butler T. Exercise-associated hyponatremia. Front Horm Res. 2019;52:178-189. doi:10.1159/000493247; Schmidt AC, Sempsrott JR, Hawkins SC, Arastu AS, Cushing TA, Auerbach PS. Wilderness Medical Society Clinical Practice Guidelines for the Treatment and Prevention of Drowning: 2019 Update. Wilderness Environ Med. 2019;30(4S):S70-S86. doi:10.1016/j.wem.2019.06.007; Zaramo TZ, Green JK, Janis JE. Practical review of the current management of frostbite injuries. Plast Reconstr Surg Glob Open. 2022;10(10):e4618. doi:10.1097/GOX.0000000000004618.

Disclosures

For this program, members of the faculty and planning committee reported nothing relevant to disclose.

Acknowledgements

Dr. Leiva was recorded at the 21st Annual Emergency Medicine Symposium: A Practical Update, held on December 8, 2023, in San Diego, CA, and presented by Cedars Sinai Medical Center. For information on upcoming CME activities from this presenter, please visit https://cedars.cloud-cme.com. Audio Digest thanks the speakers and presenters for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0.75 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0.75 CE contact hours.

Lecture ID:

IM714202

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.