Page 133 - 2022 Ranger Medic Handbook

Hyperthermia
Heat Injuries
Heat injuries fall into a continuum of heat cramps to heat exhaustion to heat stroke. While the mechanism of heat
cramps is not fully understood, there is convincing evidence to suggest it is the result of sodium depletion or overhy-
dration. Heat exhaustion and heat stroke represent a spectrum of disorders, which range in intensity and the severity
of tissue damage. The pathophysiology of heat exhaustion and heat stroke are so similar that they may represent a
continuum of disease rather than separate, distinct diseases and both are characterized by sodium and water deple-
tion. Heat cramps, heat exhaustion, and heat stroke are all illnesses related to a failure of the body to maintain fluid and
electrolyte balance to the challenge of adapting to added heat loads. These conditions may develop over several days,
allowing adequate time for effective intervention. The maintenance of adequate diet and fluid intake is essential. The use
of dietary supplements can lead to dehydration and increased likelihood of heat injury. When faced with increased heat
loads, the body is dependent on sweating to maintain a constant body temperature. The sources of the heat load may
be external (a hot day), internal (a road march with 50 pounds of gear), or both (a road march in the desert sun). If the
heat load exceeds the body’s ability to lose heat, a heat injury will result. SECTION 3
Heat Cramps
The term “heat cramps” is actually a misnomer, as muscle cramping more likely results from sodium depletion during
intense activity, not heat. In fact, cooling of a fatigued muscle is often a contributing factor. Heat cramps typically occur in
individuals undergoing prolonged, intense activity in a hot and humid environment. Heat cramps are brief, intermittent, and
very painful but can be largely prevented by maintaining an adequate salt and fluid balance prior to and during exertion.
S/Sx: Painful, tonic contractions of skeletal muscles frequently preceded by palpable or visible fasciculation. Fatigue,
dizziness, nausea, and vomiting are common.
MANAGEMENT: Obtain hydration and diet history to guide management and identify likely electrolyte cause. Use iSTAT
or similar point of care lab testing device to evaluate electrolytes if available. Oral electrolyte rehydration and foods are
the initial management of choice. IV crystalloid solution is indicated if more rapid treatment is needed. Mild stretching
and massage of the contracting muscle will provide some relief to the intense discomfort. May return to activity after
symptoms resolve but patient is at risk for return of heat cramps or other heat injury.
Heat Exhaustion/Stroke
Heat exhaustion is the most common heat illness. Although heat exhaustion in a military setting often manifests after
extreme exertion, in reality, it likely develops over several days and is a result of cardiovascular strain as the body tries
to maintain normothermia in a hot environment. Heat exhaustion occurs when the demands for blood flow (to the skin
for temperature control through convection and sweating, to the muscles for work, and other vital organs) exceed the
cardiac output. A body that has developed a state of salt depletion over several days, in combination with extreme exer-
tion, is at risk for heat exhaustion.
S/Sx: Profound fatigue, chills, nausea/vomiting, tingling of the lips, shortness of breath, orthostatic dizziness, headache,
syncope, hyperirritability, anxiety, piloerection, heat cramps, heat sensations in head and upper torso. Casualty may or
may not feel thirsty. Tachypnea, tachycardia, orthostatic hypotension may be present. Core temperature may be normal
or greater than 104ºF. Heat stroke can be defined as a heat injury with central neurological symptoms such as altered
mental status or seizures.
MANAGEMENT: Heat Exhaustion: Reduce the load on the heart with rest and cooling. Place casualty in shade and
remove heavy clothing. Apply cool water to the skin, if available. Correct water and electrolyte depletion by administer-
ing oral or IV fluids. IV fluids replenish the volume and correct symptoms quickly. Patients with resting tachycardia or
orthostatic hypotension should initially receive up to 1–2L boluses of crystalloid solution and monitored for these vital
signs to correct. If patient can tolerate oral fluids, use an oral electrolyte solution or sports drink. SM should limit activity
for minimum of 24 hours and ease into return in activity in slow stepwise approach.
MANAGEMENT: Heat Stroke: Heat stroke is a true emergency and needs to be managed by rapid active cooling (ice bath
immersion or rotation of ice sheets). In a patient with an undefined heat injury and temperature > 104º, or hyperthermia and
altered mental status treat as heat stroke per the protocol. Do not rely solely on temperature to diagnose but have a high index
of suspicion with appropriate risk factors and clinical setting and treat presumptively.
Hyponatremia
In addition to these standard heat injuries, hyponatremia, or emergently low serum sodium, may be classified as a heat
injury. Hyponatremia in our population most commonly occurs due to excessive free water intake that overwhelms the
body’s ability to maintain a normal serum electrolyte concentration. This excessive free water leads to a dilution of the
serum sodium and can have central nervous system effects such as seizures or altered mental status.
Treat all apparent heat injuries with primary concern for heat stroke. After treating or ruling out heat stroke, evaluate and
treat as indicated for hypoglycemia. In a patient thought to have a heat injury due to environmental factors with altered
mental status or seizures with a core temperature < 104°F and normal or treated glucose level, attempt to gain history
of excessive free water intake or recurrent clear vomiting. With a negative evaluation for heat stroke and hypoglycemia
in patient with altered mental status or seizures, treat for presumptive hyponatremia. Treatment includes continuing
emergent evacuation and administering a single 250mL hypertonic saline (3%) bolus. Ensure large-bore IV access for
administration and be cognizant of venous extravasation and risk with hypertonic saline.
2022 RANGER MEDIC HANDBOOK 119