Heatstroke involves multiple risk factors

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It’s that time of year when the temperature is rising and many veterinary hospitals are treating patients affected by heatstroke. Heatstroke is defined as severe pyrexia, with a dog’s body temperature rising to 104.9-109.4 °F.^1,2 This results from exposure to elevated ambient temperatures that impair the patient’s ability to dissipate the heat. These temperatures may be seen in pets that have been exposed to prolonged heat, such as those left in turned off cars or those exercised outdoors on dangerously hot days. As a result, they are less able (as seen in brachycephalic breeds) or unable to cool themselves down.

A dog’s normal temperature is maintained by a thermoregulatory center in the hypothalamus.^1,2,3 As a dog’s temperature increases, the thermoregulatory center sets into motion the various methods for cooling the animal: evaporation, conduction, convection, and radiation.^1,3 Panting is one way in which the pet can cool itself through evaporation; a second method is achieved when the pet lies on a cool surface and is cooled by conduction. Furthermore, the hypothalamus triggers a response to the increased body heat. The body constricts blood flow to the kidneys and spleen, the heart rate quickens, the blood vessels in the cutaneous tissue dilate, and panting and respiratory rate increase—all in an attempt to cool the body.

Multiple systems contribute to the risk of heatstroke and are negatively affected by it. The risk factors include but are not limited to brachycephalic syndrome, obesity, laryngeal paralysis, cardiac disease, and tracheal collapse.^2,3 The degree of damage to the body correlates with the body temperature attained and sustained, along with the span of time during which the body had been under stress. Generally, these patients present with a history that can lead to a diagnosis of heatstroke; careful consideration should be given if the information doesn’t coincide with the patient’s history. Other conditions such as meningitis, encephalitis, toxicities causing seizures, and brain lesions may be the cause of hyperthermia.^1,2

Clinically, these patients will often present acutely panting, tachycardic, with bounding pulse, and temperatures above 104.9 °F.¹ These signs can progress to weak pulses; muddy, dry mucous membranes; vomiting; diarrhea; seizures; and central nervous system depression.³ Time is of the essence in such cases, because it is paramount to begin therapy/cooling to stabilize the patient and bring their temperature down to 103 °F, at which point therapy can be stopped.^2,4

Foremost, consider whether the patient is out of the heat and in a cool area before administering treatment. Then begin to saturate the patient’s fur with cool water, because the goal is to reduce body temperature by increasing peripheral blood flow and dilating peripheral vessels. It is important that cooling measures employed do not make the patient too cold, because it could result in more vasoconstriction, which is known to shunt blood to the patient’s core, resulting in further increase of the core temperature and additional damage.² Cool compresses or soaked towels placed over axillary areas and femoral vessels, with the addition of circulation air provided by a fan, will make significant differences in cooling efforts.¹

Although these methods of cooling are being initiated, an intravenous catheter should be placed to administer fluids or emergency medications, taking into consideration the individual needs of the patient. As the body responds to heat by vasoconstriction, care must be taken to prevent fluid overload, which can negatively affect the lungs and brain.¹ When treating acute heatstroke, evaluation of the patient’s needs for fluids should be determined on an individual basis. Fluids should be administered at room temperature or through a cool water bath in order to be effective. Fluid rates and administration should be continually monitored, because the hemodynamic state of the patient may change depending on the patient’s physiological response to therapy/cooling.

After identifying the individual needs of each patient, note that there are various classes of medications that can be used or considered when treating heatstroke. The use of nonsteroidal anti-inflammatory drugs is contraindicated. Nonsteroidal drugs act to adjust the hypothalamic set point for temperature and therefore may cause more harm than good.¹ They also may create further damage to the already stressed kidneys and stomach. Corticosteroids may be used on a case-by-case basis for complications of heatstroke like cerebral edema. The use of antibiotics has been proven beneficial, because the risk of translocation of bacteria from the gastrointestinal tract is high.

The selection of antibiotics should be directed toward a broad-spectrum option that should be administered until the patient’s gastrointestinal signs have resolved and appetite and bowel movements have returned to normal.³ With antibiotic support, gastrointestinal protectants may also be considered, because the goal of these medications should be to prevent gastrointestinal ulcers and alleviate nausea and acid production.³ Severely compromised patients may need both central nervous system and cardiac support. Mannitol or hypertonic saline may be used to decrease intracranial pressure and improve coronary, microvascular, and cerebral blood flow, but it should be used with caution when the patient is dehydrated.² Diazepam may also be used to assist in controlling seizures in patients.² Ventricular arrhythmias, the most common arrhythmia seen in patients with heatstroke, should be treated with lidocaine.³

Ideally, patients should be monitored using electrocardiography, a pulse oximeter, a thermometer, and a blood pressure monitor. A baseline of temperature, pulse, respiration, capillary refill time, and mucous membrane color should be documented and the parameters serially recorded as the patient responds to treatment. If available during hospitalization, packed cell volume, total protein, prothrombin time, partial thromboplastin time, blood glucose, electrolytes, urine output volume, and lactate tests are recommended.⁴

The prognosis for patients with heatstroke is dependent on the degree of hyperthermia and the time it takes for the patient’s body temperature to return to normal.³ The owners should be informed that the prognosis is considered guarded to poor.⁴ Patients that do not do well within 24 hours of presentation do not survive. Some of the negative prognostic indicators include arrhythmias, coagulopathies, and a poor neurologic response to treatment.²

As we are all aware, client education regarding the prevention of heatstroke is of utmost importance and can be lifesaving. This education should start during puppy visits and should be revisited with the change in season on a yearly basis. It is often helpful to post warning signs in the veterinary clinic and on social media. Some patients living in different climates may acclimate better than others but, overall, erring on the side of caution is always best.

Patricia M. Leff, who earned her DVM degree from the University of Florida College of Veterinary Medicine, practices at Brick Town Veterinary Hospital in Brick, New Jersey.

References

1. Hackett T. Life threatening emergencies. In: Wingfield WE, ed. Veterinary Emergency Medicine Secrets. Hanley & Belbus; 1997: 40-43.
2. Canine Heat Stroke. Iowa Veterinary Specialties. Accessed August 16, 2020. http://www.iowaveterinaryspecialties.com/student-scholars/canine-heat-stroke-literature-review
3. Tabor B. Heatstroke in dogs. Today’s Veterinary Practice. September/October 2014. https://todaysveterinarypractice.com/todays-technician-heatstroke-in-dogs/
4. Plunkett SJ. Traumatic emergencies. Emergency Procedures for the Small Animal Veterinarian. Elsevier; 1993: 45-47.