Clinical Gems: Approach to Heat Stroke
By: Rebecca Syring, DVM, DACVECC
Board-Certified Critical Care Specialist
Veterinary Specialty & Emergency Center
Summer means daylight stretching long into the evening hours and increased time spent outdoors. This is great for us and our pets as physical activity and socialization are often much needed after hibernating throughout the cold winter and wet springs. While exercise and activity are good for everyone, our pets included, there is always the risk for too much of a good thing.
Educating clients and staff alike as to the dangers and warning signs of overheating in pets is critical in helping prevent, and be ready for, heat stroke.
Unfortunately, our canine companions tend to be people pleasers and often lack that common sense filter that tells them to stop when they are overdoing it. We see heat stroke in all shapes and sizes of dogs as a result of either increased heat production or reduced heat dissipation. Certainly the overweight brachycephalic dog or the older Labrador retriever-type dog with laryngeal paralysis who go for short walks on a warm day are two of the more common scenarios seen in the ER at VSEC.
In these scenarios, just a little bit of activity on a hot or humid day can lead to rapid overheating. In these dogs, impaired evaporative heat loss through ineffective ventilation results in a vicious cycle. They pant in an attempt to promote heat loss, which results in upper airway obstruction from edema and ultimately leads to worsened panting causing excess muscle activity and more heat generation. Other common heat stroke victims include dogs exposed to extreme heat if left in a car on a hot day, left outside without shelter from the sun, or the dog that willingly runs alongside its owner on a trail simply overdoes it because of a will to please.
Heat stroke can be fatal if not promptly corrected, causing a systemic inflammatory disease state, resulting in multiple organ dysfunction as a result of cellular dysfunction and necrosis. Many of these patients die from complications such as acute renal failure and disseminated intravascular coagulation (DIC) due to prolonged heat exposure and its side effects.
- A 2006 study of 54 dogs with heat stroke demonstrated at 50% mortality rate, with delay in hospitalization >90 minutes from onset of heat stroke, obesity, seizures, detection of hypoglycemia, thrombocytopenia or prolonged PT/PTT on admission or persistence of azotemia beyond 24 hours of therapy associated with poor outcome.
- A 2009 study demonstrated that dogs with >18 nucleated red blood cells/100 white blood cells at hospital admission had a 91% sensitivity and 88% specificity for mortality – therefore blood smear analysis and manual differential should be considered in dogs with heat stroke to help prognosticate on hospital admission.
The single most important tip for the heat stroke patient is early, rapid cooling of the core body temperature. When possible owners should be advised to quickly wet down the pet with a hose and then rapidly proceed to the nearest veterinary facility. If this is not readily achievable, the pet should be immediately transported in a cool car with cross-ventilation.
Once at the veterinarian, a body temperature should be taken and cooling measures instituted until the body temperature is 103.6-104.0F, at which point external cooling is removed (see more below). If an underlying cause for hyperthermia is present, other than environmental exposure, it should also be addressed or cooling measure will be for naught.
If the patient is seizing, valium or midazolam (0.25-0.5 mg/kg IV) should be administered to stop seizure. This can be repeated 1-2 times. If ineffective, additional anticonvulsants such as IV levetiracetam (20-40 mg/kg IV) or phenobarbital loading may be required.
If the patient is agitated, dysphoric or paddling, sedation should be considered. My preference is butorphanol 0.2-0.3 mg/kg IV/IM and I’ll avoid acepromazine until cardiovascular stability is achieved. When acepromazine is used, I often only use 0.005 mg/kg IV doses to achieve sedation.
If the patient has signs of upper airway obstruction (inspiratory stridor, respiratory distress), sedatives can be considered but often intubation will relieve the airway obstruction and result in rapid temperature reduction by establishing effective ventilation. Anti-inflammatory doses of corticosteroids (Dexamethasone SP 0.1 mg/kg IV) can be used for excessive upper airway swelling.
How to cool the patient:
- My preferred method of cooling involves wetting the fur of the pet with cool water then directing a fan at the patient to move heat away from the body, which increases convective cooling.
- While submerging the patient in a tub of cool water can be used, it is often more cumbersome and can result in excessive cooling.
- I do not advocate placing alcohol on footpads or running fluids through ice water, as these as an ineffective means of cooling and just an extra task for your already busy staff.
- Do not wrap patients in wet towels, as this tends to trap heat.
- External cooling should be stopped once the body temperature reaches 103.6-104.0F to prevent over-correction and hypothermia. The patient should be towel dried and fan removed.
- Rectal temperature should be rechecked every few minutes during cooling until the target temperature has been reached. If you have an ECG monitor with a rectal temperature probe, this is an excellent way to continuously monitor temperature and an alarm limit can be set to notify you when the target temperature is achieved.
While cooling the patient, IV access should be established and isotonic crystalloid fluids administered to improve circulation with a goal of normalizing blood pressure and optimizing tissue perfusion. Patients with heat stroke frequently develop profuse, and often bloody, diarrhea secondary to both reduce GI perfusion and heat stress to the gastrointestinal mucosa when present high rates of fluids are needed to keep up with losses. Antibiotics, directed against gram negative and anaerobic bacteria, should be used to reduce the risk for bacterial translocation in this scenario. Acute renal failure, coagulopathy, brain injury and cardiac arrhythmias are some of the more common sequela to heat stroke. Petechia may be noted when clipping the fur for catheter placement and coagulation testing (PT/PTT clotting times and assessment of platelet count) should be performed in pets that have sustained heat stroke. If a coagulopathy is documented, plasma transfusion will be needed.
Mentation changes are common in these patients – a blood glucose should be assessed and hypoglycemia corrected with intravenous dextrose solutions. If mentation changes persist despite correction of perfusion and/or hypoglycemia, mannitol (0.25-1.0 gram/kg) can be considered as an IV bolus over 20-30 minutes and elevating the head/neck 15-30 degrees above horizontal should be considered to address presumed intracranial pressure increases. Renal values should be assessed on admission and serially evaluated throughout patient stay. When a concern for acute kidney injury is present, urinary catheterization and monitoring of urine output with a goal of >2 ml/kg/hr is recommended.
Cardiac arrhythmias are common in these patients – if needed, lidocaine is recommended as the first line of defense for ventricular arrhythmias, not only for its antiarrhythmic properties but also for its anti-inflammatory effects, which can be beneficial to the patient as a whole.
Heat stroke can be a devastating injury to our pets. With rapid intervention focusing on quickly cooling the patient and establishing tissue perfusion, we have the best chance of a good outcome in the patients. As always, whenever you have such a patient in your clinic, VSEC’s emergency and critical care department is available to help you with these patients and can provide the detailed intensive care many of these patients will require to give them the best chance at a good outcome!
Dr. Rebecca Syring, is a Board-Certified Emergency & Critical Care Specialist at the Veterinary Specialty & Emergency Center. The Veterinary Specialty & Emergency Center operates state-of-the-art emergency and specialty veterinary hospitals that are open 24/7/365 in both Levittown PA and Philadelphia PA. For more information about our world-class emergency and specialty care, please visit VSEC on the web at www.VSECVET.com.