Exam 4 - Canine Heatstroke Flashcards
what is heat stress?
perceived discomfort & physiological strain associated with exposure in a hot environment
what is heat exhaustion?
mild o moderate illness due to water or salt loss
thirst, weakness, discomfort, anxiety, fainting
core temperature may be normal, low, or slightly elevated
what is heat stroke?
core body temperature > 105.8 F
central neurologic dysfunction
varying degrees of organ dysfunction
what are the 2 types of heat stroke?
environmental (classic) - due to high temperatures
exertional - due to strenuous exercise
or combination of both
what are some examples of causes of heat stroke?
exercise/heat, seizures, pyrexia, eclampsia, amphetamines, metalaldehydes, macademia nuts, organophosphates
what are some risk factors associated with heat stress?
intact male, geriatric, brachycephalic, dense/dark hair coat, CV disease, neuro disease, confinement, humidity, furosemide, b-blockers, & phenothiazines
why is acclimatization important in animals? what are some components?
gradual adaptation to increasing temperatures
increased CO, activation of RAAS, salt conservation, water conservation, increased GFR, & resistance to rhabdomyolysis
how long does the acclimatization process take?
takes 60 days but starts in 10-20 days
what are the effects of increasing heat on the hypothalamus?
temperature increases <2F activates thermoreceptors
renal & splanchnic vessel constriction, cutaneous vasodilation, activation of RAAS, catecholamine release, & activate panting center
why is it important that nearly all cells produce heat shock proteins?
it helps stabilize other proteins & cellular integrity
protects against oxidative stress
decreased production with age & genetics
what is the acute phase response in regards to the effects of heat in cells?
immune & inflammatory response - can be protective or destructive
what is the difference between humans & animals when it comes to adapting to heat?
humans acclimate by increasing the sweat response
animals are more dependent on evaporation - especially when the temp is > 89.6 F - panting increases evaporation from oronasal mucosa
T/F: evaporation stops being useful when humidity is > 80%
true
what are the damages seen when an animals temperature hits 105.8? 109.4? 120.2?
105.8 - possible permanent CNS damage
109.4 - severe tissue injury
120.2 - tissue necrosis
what is the shock organ of the dog?
gi tract
what are some clinical signs seen in a dog with heat stroke?
CNS depression, petechia, panting, dry MM, absent/rapid CRT, vomiting/diarrhea, variable pulse quality
what is the best way to cool a heat stroke animal off?
put a cold t-shirt on them, iv fluid therapy, & put fans on them - stop at 103/104F
what are some less effective ways to cool a heat stroke animal off?
cold IV fluids, ice water bath, ice water lavage, & ice water enema
what is happening inside the body at 106-107F temperatures?
endotoxin translocation from the gi tract
apoptosis in liver, spleen, lymph nodes, & gi mucosa
what is happening inside the body at 109.4F?
uncouples oxidative phosphorylation
proteins denatured
what are the cardiovascular effects of heat stroke?
initially increased cardiac output - renal & splanchnic vasoconstriction
eventual decompensation - splanchnic vasodilation & cutaneous vasodilation, venous pooling, decreased circulation leads to decreased heat removal
arrhythmias are common
what are the coagulation abnormalities seen with heat stroke?
coagulation & fibrinolysis are activated by heat - consumption of coagulant & anticoagulant factors with coagulation factors remaining activated even after cooling
direct platelet activation & endothelial damage
eventual widespread thrombosis & hemorrhage
what are the mechanisms of the gi effects seen in heat stroke?
direct thermal injury & hypoperfusion & microthrombosis
what gi side effects are seen with heat stroke?
translocation of endotoxin, ileus, vomiting/diarrhea, mucosal sloughing, & protein loss
what are the mechanisms of renal effects caused by heat stroke?
direct thermal injury, hypoperfusion & microthrombosis, & myoglobin excretion
what are the side effects of renal injury caused by heat stroke?
AKI - creatinine elevations with 48 hours - need to monitor urine output
what can be used as a prognostic indicator or a patient in heatstroke with renal signs?
elevated creatinine at 24 hours - poor prognosis
what are the side effects of liver injury caused by heat stroke?
elevations in liver enzymes are nearly ubiquitous - ALT, AST, ALP
dysfunction - increased total bilirubin, decreased glucose, & decreased cholesterol
what are the mechanisms of liver effects caused by heat stroke?
direct thermal injury & hypoperfusion & microthrombosis
what are the mechanisms of neurologic damage caused by heat stroke?
thermal injury to the brain & neurons
cerebral edema
hypoperfusion & microthrombosis
T/F: the persistence of neurologic effects is associated with mortality in heat stroke patients
true
T/F: dog brains are more resistant to heat injury in cases of heat stroke causing neurological signs
true
what are the mechanisms of pulmonary damage caused by heat stroke?
pulmonary edema, aspiration, thermal injury, & microthrombosis leading to respiratory distress
what may be seen on hematology of a patient with heat stroke?
hemoconcentration, nucleated red blood cells!!!
thrombocytopenia, hypersegmented neutrophils, spherocytes, & ecchinocytes
what is the most important marker seen on chemistry of a heat stroke patient? what other abnormalities may be seen?
hypoglycemia - may be due to consumption or liver dysfunction, especially if refractory to treatment
elevated CK
azotemia - pre-renal vs renal
elevated liver enzymes - ALP, ALT, AST & possible evidence of dysfunction seen in increased bilirubin & decreased cholesterol
what bloodwork testing should be done in a recovering heat stroke patient?
CBC at least every other day until normalized & check smears daily for platelets
hepatocellular values every 1-2 days until stabilized
kidney values every 12-24 hours until stabilized
electrolytes every 4-24 hours until stabilized
why must you retest your coag panel in a heat stroke patient at 12 & 24 hours?
PT & aPTT are often prolonged but it can be a delayed effect
what are some negative prognostic indicators of heat stroke?
longer duration of exposure, hypothermia/coma upon presentation, hypoglycemia, nucleated RBC, elevated creatinine at 24 hours, abnormal PT & PTT at 12/24 hours, & MOD
how do you prevent heat stroke patients from becoming worse?
rapid cooling & then maintaining their temperature
maintain organ perfusion - fluid support without over-hydration & potential vasopressor support
frequent monitoring - vital parameters, laboratory values, & mentation/coma scoring
antibiotics
plasma
why should you not use alpha-2 agonists in heat stroke patients?
they significantly drop CO & elevate PVR without improving perfusion
why should you not use NSAIDS in heat stroke patients?
not for patients in shock!!! increased risk of AKI
why should you not use steroids in heat stroke patients?
they don’t improve survival & increase the risk of infection
what is the main goal when cooling off a heat stroke patient?
maximize evaporative cooling - no ice
what is the general prognosis for heat stroke patients?
50/50 - prognosis isn’t readily apparent
