A FEW WORDS... Managing Hyperthermia in Dogs (from Ep 6)

These patients—typically bulldogs or pugs—often arrive after exercise on a warm day or even during the relative cool of the night after a hot day.   In these night-time presentations, hyperthermia is a consequence of upper airway obstruction, panic, and increased respiratory effort rather than environmental heat alone.  

I've had many patients, especially Frenchies, arrive with frequent coughing up of thick white foamy saliva. However, their primary problem is upper airway BOAS obstruction and hyperthermia.

Here is how to approach and manage hyperthermia in these critical cases.

1. Immediate Stabilization & Oxygen

Your first priority is to calm the patient and improve their breathing without adding more stress.

 * Sedation FIRST: Brachycephalic patients are often caught in a cycle of panic and increased respiratory effort. Using butorphanol (HIGH 0.3 mg/kg IM) for sedation to help break this cycle. There are minimal negative risks to using this short acting, poorly analgesic opioid. For patients in which the butorphanol is insufficient to calm them, Charlotte uses dexmedetomidine or medetomidine (LOW doses to minimise respiratory depression and cardiovascular depression but maximise sedation, 3-5 ug/kg IV or IM). Cardiovascular effects are profound and so is respiratory depression. So, it is important to consider these negative effects. Unfortunately, ACP (acepromazine) which Brendan prefers  (IV, moderate doses) also causes hypotension which is irreversible and long-lasting, which could be problematic if patients are hypovolemic for example. In general practice environments, in which trained staff and patient one-on-one time is limited, ACP demands slightly less minute by minute monitoring than an alpha-2 against, and has anxiolytic, anti-emetic and hypothermic benefits and it's long duration can indeed be helpful in more stable patients. 

 * Oxygen: I personally do not usually do this too ardently before sedation as it's more likely to cause additional stress. Use flow-by, a mask (if tolerated), or nasal prongs. Small dogs with hyperthermia would not suit an oxygen cage or crate as they will not be amenable to rapid cooling. Once sedation has kicked in, it is usually easier to oxygenate the patient without extra stress. 

* Carbon Dioxide & Ventilation: Please note that supplying oxygen is only part of the issue as some of these patients are not expiring their CO2 (i.e. poor ventilation) and so need intubation and ventilation just as much as supplemental oxygen. 

* IV access and draw blood for biochemistry, elecs and haematology. A venous EPOC to include lactate and vCO2 is very helpful in guiding the decision to intubate and progression. Hypoglycemia is reported in these patients.  And identifying haemoconcentration (raised HCT) which may indicate hypovolemia or the presence of azotemia are both very helpful for fluid management and deciding the suitability of acepromazine given its prolonged hypotensive action. 

* Dexamethasone IV ?? Corticosteroids are controversial. While sometimes administered to address suspected upper airway oedema, there is limited evidence for benefit in acute brachycephalic crisis, and potential risks include GI ulceration and delayed recovery. If used, they should not delay definitive airway management.

2. Airway Control & Anaesthesia 

 * Be prepared: to give IV propofol to induce the patient and intubate. 

Do not hesitate if the patient is very cyanotic, becoming weak or losing consciousness, even if core temperature is improving.  Act quickly and decisively. Deliberating too long is riskier than inducing and intubating. 

Anaesthesia and intubation substantially improves the patient’s oxygenation, ventilation and distress. Try to maintain anaesthesia with a propofol CRI (approximately 0.5mg/kg/minute and adjust as necessary), but I use mini boluses of propofol to keep the patient anaesthetised whilst you are organising the propofol CRI and dosing.

Deciding when to wake the patient up is problematic. I'll sometimes transition to a dexmedetomidine CRI to slowly recover my patient and slowly extubate. However, that's when I'm in OOH emergency practices with experienced staff on hand to adjust the CRI as needed and carefully monitor vitals.   

In general, I may continue the propofol CRI for approximately 15-30 minutes allowing the breathing and vitals to normalise before waking up the patient.

3. Aggressive Cooling Techniques

We both like to combat hyperthermia rapidly to prevent further decompensation.  Though, just reducing core body temperature is not usually enough alone, as the distress and possible airway compromise/oedema will continue to cause problems if not addressed.  Patients may continue to ventilate poorly despite normalised temperature, and hyperthermia may recur without proper attention to these other issues. 

Some clinicians much prefer more gentle cooling due to concerns about vasoconstriction and reduced cooking effect. 

   * Immersion/Cold Water: While some suggest tepid water, many emergency clinicians advocate for cold water immersion to bring the temperature down as fast as possible, as slow cooling can be risky in critical patients. Pouring a jug or two of water over their back often provides insufficient cooling as insulating air is trapped within the dense fur and prevents the water evaporating from the hot skin.

   * Fans & Airflow: Place electric fans directly on the patient to facilitate evaporative cooling.  Be aware of electrical risk. 

   * Avoid Wet Towels:  Though wet towels alongside fans can cool patients, it is likely faster to cool a patient without covering them and increasing evaporative heat loss. 

   * Strategic Clipping: If the animal has a thick coat, clip the fur to allow better airflow and contact with water.

   * Alcohol on Extremities:  Not my favourite one, because I am immersing my patients, but it is not wrong.  Does need a lot of alcohol to be effective, and alcohol needs re-application once evaporated.

4. Monitoring and When to Stop

Active cooling should be monitored every 5-10 minutes to avoid overshooting into hypothermia, which is a common issue.

 * Stop active cooling at 39.5C (103.1°F).  The calm, sedated patient will usually continue to cool to 38.5C without aggressive cooling. 

 * Environmental Heat: Be aware that oxygen cages and tents can get very hot; monitor the patient’s temperature frequently while they are inside these units.

* Keeping the patient cool and calm is important for the next 6-12 hours. 

4. After-care

* Aspiration pneumonia: this is a potential risk to be aware of. 

* Re-bound hyperthermia: fairly common over the next 6-12 hours. 

* Dehydration: Address possible dehydration.

* BOAS Surgery: Discussions with the client on BOAS assessment and surgery should be considered in some patients depending on their sensitivity to heat and exercise-induced hyperthermia.

* Cooling options at home: Discuss cooling options for patients at home during hot weather, such as cooling jackets and mats, paddling pools, fans and exercise-avoidance.