Pathophysiology of heatstroke in dogs – revisited 2017

Question 1

What temperature cut off is considered as heatstroke?

Answer 1

> 41°C

Question 2

Which breeds are overrepresented

Answer 2

Golden, lab, brachycephalic, Belgian and Dutch shepherds (military dogs)

Question 3

Why are brachycephalic dogs overrepresented?

Answer 3

ineffective evaporative ability due to stenotic nares, elongated soft palate and hypoplastic trachea and laryngeal edema

Question 4

What is Hereditary exercise-induced collapse (EIC)?

Answer 4

Episodic limb weakness, ataxia and collapse,
has been described in Labrador retriever dogs,
and might thus account for some heatstroke cases
in this breed.

Question 5

Which breed is affected by induced malignant hyperthermia?

Answer 5

English Springlers Spaniels

Question 6

What happens?

Answer 6

Moderate exercise results in collapse, dyspnea,
hyperthermia and hyperlactatemia

Question 7

Patophys of it

Answer 7

Calcium homeostasis
defect, due to ryanodine receptor (RYR) calcium
release dysfunction

Question 8

What environmental factor affects evaporation in dogs?

Answer 8

Humidity:
>35% -> less effective
>80% -> neglected

Question 9

What are the main causes of death in dogs with heatstroke?

Answer 9

systemic hemodynamic deterioration and pulmonary lesions (postmortem)

Question 10

What is seen in brain histopathology followed by heatstroke?

Answer 10

cerebral
edema, hemorrhage, hyperemia, and neuronal necrosis.

Question 11

Brain damage is caused secondary to…

Answer 11

shock, MODS, bleeding, micro thrombi more than direct brain tissue thermal injury as dogs have intrinsic thermal
resistance, protecting it from direct thermal injury.

Question 12

Explain the muscle damage and rnhabdomylosis occurring in the HS

Answer 12

Rhabdomyolysis is a prominent feature of heatstroke
in dogs, occurring during and following the heat
insult, and is exacerbated during the first 24 hrs of
hospitalization due to skeletal and cardiac muscular
hypoperfusion, resulting from hypovolemic, distributive
shock and microthromboses, secondary to developing
DIC.

Question 13

How can we confirm rhabdomyolysis in human and dogs?

What other parameter can we look at in dogs?

Answer 13

Human: serum and urinary myoglobin concentration.
In dogs, the human-based myoglobin immunoassays are insensitive, and currently no myoglobin immunoassay has been validated for use in dogs.

CK

Question 14

What is the pathogenesis of AKI in heatstroke?

Answer 14

Multifactorial: direct renal thermal injury, decreased renal perfusion due to hypovolemic, distributive shock and dehydration, endotoxemia, myoglobulinemia secondary
to rhabdomyolysis, release of cytokines and vasoactive
mediators and microthromboses, associated with DIC

Question 15

How is the blood pressure at presentation in animals with naturally occurring heatstroke and why?

Answer 15

Normotensive. Because they present in the compensatory phase (neurohormonal
compensatory mechanisms to maintain blood pressure
react fast).

Question 16

List risks factors which ultimately worsen the prognosis (result of dx test on presentation, during hosp etc)

Answer 16

Obesity, prolonged
(>90 min) time-lag from the occurrence of the heat
insult to presentation for veterinary care, hypoglycemia
(glucose <47 mg/dL) at presentation, azotemia
(serum creatinine concentration >1.5 mg/dL) at 24 hours post presentation, and occurrence of DIC,
AKI, ventricular arrhythmia, seizures and abnormal
mental status.

Question 17

What extra-cardiac mechanisms were proposed as
contributing processes to myocardial damage and
development of cardiac arrhythmias?

Answer 17

myocardial
hypoperfusion and injury, lactic acidosis, hypoxemia,
electrolyte imbalance and possibly, direct thermal
injury

Question 18

What markers are increased in heatstroke?

Answer 18

Serum cardiac troponins I and T concentrations

Question 20

What is an excellent prognostic marker for prediction
of secondary complications as well as survival?

Answer 20

Pathologic metarubricytosis (nucleated cells)

Question 21

What parameters are included in their severity scoring system and predict outcome?

Answer 21

the PT, aPTT and hemoglobin concentration,
occurrence of petechiae,
AKI, shock, DIC and seizures

Question 22

What was the sensitivity and specificity?

Answer 22

93% 86%

Question 23

Name some potential novel molecular biomarkers

Answer 23

HSP72, histones