EM Heatstroke + Hypothermia

Definition:

Thermoregulation

Process of maintaining an internal temperature within a tolerable range.

What part of the brain determines the body's "set point" or normal temperature range?

hypothalamus

Endogenic VS Exogenic Heat Sources

- Endogenous = muscle activity, metabolism

- Exogenous = outside the body

What 4 methods are used to dispel heat from the body?

- Conduction: heat is conducted away from the body by contact with a cool surface

- Convection: heat is carried off the body by contact wit cooler, circulating air

- Evaporation: As liquid becomes vapor, the surface holding the liquid cools

- Radiation: heat moves from the body into the air w/out the assistance of circulating air

What are the 2 types of hyperthermia?

- Pyrogenic: caused by infection or inflammation; FEVER - the body will not try to cool itself

- Nonpyrogenic: not caused by infection or inflammation; the body will attempt to cool itself unless the thermoregulatory center is damaged

What are the 2 classifications of heatstroke?

- Exertional: occurs when an animal is worked or exercised in an environment it has not acclimated to; working dogs, competition dogs

- Nonexertional : animal cannot dissipate heat because of decreased airflow, lack of shade, no access to water, increase in temperature, or increase in humidity; dog tied out in the sun, locked in a car, confined in a kennel in an airplane cargo hold, etc.

What are predisposing factors of heatstroke?

Laryngeal paralysis
Brachycephalic airway
Tracheal collapse
Heart disease
Obesity

Effects of Heatstroke on the Body:

Cardiac

Vasodilation eventually occurs, causing venous pooling and decreased plasma volume/cardiac output, myocardial ischemia, and arrhythmia.

Effects of Heatstroke on the Body:

Pulmonary

- Noncardiogenic pulmonary edema
- Acute respiratory distress syndrome (ARDS)
- Decreased oxygen uptake by tissues = ischemia = myocardial damage = cardiovascular collapse

Effects of Heatstroke on the Body:

GI

- Liver damage
- GI barrier fails - bacterial translocation - SIRS/SEPSIS/MODS
- Widespread ischemia

Effects of Heatstroke on the Body:

Muscular

Rhabdomyolysis results from thermal injury to muscles; myoglobin is released, which is nephrotoxic = renal failure

Effects of Heatstroke on the Body:

Coagulation

Damaged endothelium = initial thrombosis followed by DIC

Effects of Heatstroke on the Body:

Neurologic

- Cell death = hemorrhage, cerebral edema

- Seizures

- Brain damage can occur at 105.8°F

Effects of Heatstroke on the Body:

Renal

- Decreased cardiac output and renal vasoconstriction = decreased renal perfusion; add dehydration = renal tubular necrosis
- Azotemia

Heatstroke Presentation includes ...

Presentation will depend on the animal’s compensation and the stage of shock!

- Altered mentation, collapse, ptyalism, V+/D+, panting

Heatstroke Diagnostics include ...

CBC, chem, coagulation panel, urinalysis, blood gas, blood smear, blood glucose, PCV/TS, ECG

Heatstroke Treatment includes ...

- # 1 treatment: cooling the patient

- Supplement oxygen

- Fluid resuscitation

- Serial blood pressure monitoring

- Blood products

- Dextrose

- Anti-arrhythmics

Primary VS Secondary Hypothermia

- Primary - due to cold exposure outside/water

- Secondary - disease, toxin, medications, anesthesia

Active VS Passive Rewarming for a Hypothermic P

- Passive - external covers (blankets etc)

- Active - external and core

What are the 2 types of active rewarming?

- External: (for moderate hypothermia = 82-90°F) transfer of heat from heat generating device - risk of burn

- Core: (for severe hypothermia= <82°F) pleural/peritoneal lavage, warmed O2, warmed IV fluids, warm enemas/bladder lavage

What are some complications for rewarming a hypothermic patient?

- Temp may still drop afterwards

- Rewarming shock - caused by vasodilation as a result of applied heat

- Heating pad burns