heat stroke Flashcards
Heat stroke can be classified as
Heat stroke is generally associated with multiorgan derangements, but ….is the hallmark of the condition.
Every body system can be involved, but the major ones affected
Treatment involves
exertional (overheating while exercising)
nonexertional (classic heat stroke).
central nervous system dysfunction (ranging from mild to moderate altered mentation to seizures or coma)
cardiovascular, central nervous, gastrointestinal, renal, and coagulation systems.
cooling the patient, providing aggressive suppor care.
worse prognosis in dogs has been associated with
hypoglycemia, < cholesterol level, > bilirubin hypoalbuminemia ventricular arrhythmias >creatinine values longer delay from incident to treatment obesity seizures prolonged PT, aPTT, DIC > number of nucleated red blood cells.
Heat cramp is characterized by muscle spasms resulting from
heat prostration or heat exhaustion CS:
hallmark of heat stroke is
more recent definition of heat stroke describes it as a form of
sodium and chloride depletion
fatigue, weakness, muscle tremors, vomiting, and diarrhea occur
severe central nervous system (CNS) disturbance, and it is often associated with multiple organ dysfunction
“hyperthermia associated with a systemic inflammatory response leading to a syndrome of multiorgan dysfunction in which encephalopathy predominates.”
Body temperature increases when heat load exceeds heat dissipation. Heat dissipation may occur via four mechanisms:
70% of heat loss in dogs and cats occurs by
facilitated by increased cutaneous circulation as a result of increased cardiac output and sympathetically mediated …
convection, conduction, radiation, and evaporation
radiation and convection through the skin
peripheral vasodilation
Shunting of blood to the periphery involves a trade-off with blood supply to the
Significant heat loss also occurs as a result of evaporation from the respiratory tract through panting, and this becomes the predominant mechanism of heat loss when
viscera (intestines and kidneys)
ambient temperature is equal to or greater than body temperature
the two most common heat loads experienced by dogs that may cause extreme hyperthermia are:
Respiratory evaporative loss is diminished by
work of breathing in these latter conditions can contribute substantially to the heat load
warm-humid environment
humid climatic conditions
upper respiratory tract abnormalities such as brachycephalic conformation, laryngeal paralysis or airway masses, or collapsing trachea
Diminished radiational and convective heat loss from the skin may occur as a result of
hypovolemia from any cause, poor cardiac output, obesity, extremely thick hair coat, or lack of acclimatization to heat
Situations that combine high heat load and diminished heat dissipation may result in a rapid and extreme body temperature increase
In humans, acclimatization to heat can take:
is associated with enhanced:
2 weeks or longer
- cardiac performance
- salt conservation by the kidney and sweat glands through activation of the renin-angiotensin-aldosterone axis
- increased capacity to sweat
- plasma volume expansion
- increased GFR
- increased ability to resist exertional rhabdomyolysis
Increased body heat induces three protective mechanisms:
The acute-phase response involves a variety of
Proinflammatory mediators induce
thermoregulation (mentioned previously)
acute-phase response
increased expression of intracellular heat shock proteins
proinflammatory and antiinflammatory CK
leukocytosis
promote synthesis of acute-phase proteins
stimulate hypothalamic-pituitary-adrenal axis
activate endothelial cells and white blood cells
mediators are protective for the body when balance is maintained between the proinflammatory and antiinflammatory sides.
heat shock proteins protect the cell and the body against further heat insults; they protect against
Heat stroke results from a failure of thermoregulation followed by an exaggerated
Additionally, absorption of endotoxin from
denaturation of intracellular proteins
help to regulate the baroreceptor response during heat stress, preventing hypotension - cardiovascular protection
acute-phase response and alteration of heat shock proteins
GI tract may fuel the inflammatory response
intestinal mucosal permeability is increased during heat stress
many of the mediators involved in heat stroke are the same mediators associated with
sepsis and the systemic inflammatory response syndrome
suggested pathophysiologic sequence in heat stroke involves initial production and release of
from the
increased systemic levels of
from the
factors mediate excessive activation of ___&___
which results in release of numerous
as well as activation of
interleukin-1 and interleukin-6
muscles into the circulation
endotoxin
GI tract
leukocytes and endothelial cells
proinflammatory and antiinflammatory cytokines
coagulation and inhibition of fibrinolysis
Direct endothelial cell injury due to the heat, combined with an initial hypercoagulable state, results in
These proinflammatory and procoagulation processes and direct heat injury can lead to
animals should be assessed and monitored for multiple organ failure, with particular attention to the
microthrombosis and progressive tissue injury. These proinflammatory and procoagulation processes
multiple organ dysfunction syndrome
respiratory cardiovascular renal GI central nervous systems coagulation system
Glucosuria may be detected despite normal or even low blood glucose
suggests:
proximal tubular damage or
recent hyperglycemia with glucosuria
The most common CBC abnormality:
associated with a worse prognosis.
a value of ____ or more per ____
at presentation had a sensitivity and specificity
typically decreases rapidly over the first
NRBCs
18 or more NRBCs per 100 leukocytes
at presentation
91% and 88% respectively for predicting death
24 hours
cooling methods:
Evaporative methods include:
in humans, ice water is used in this method, but recommendations are to:
- wetting the dog’s whole body w tepid water
- blowing fans over the body
massage the muscles to maintain circulation because extreme cooling of the periphery may result in vasoconstriction and paradoxical inhibition of evaportation
alcohol on paw pads -
not extensively researched but intuitively inefficient
External conduction cooling techniques include:
Internal conduction techniques:
Pharmacologic techniques:
ice packs over major vessels (e.g., jugular veins)
tap water immersion
ice water immersion
cooling blankets
ice water baths may produce peripheral vasoconstriction and thus diminish heat dissipation overall
iced gastric lavage, iced peritoneal lavage, and cold water enemas, although the latter may interfere with temperature monitoring
dantrolene sodium have been evaluated experimentally and have not been effective
-postsynaptic muscle relaxant that lessens excitation-contraction coupling in muscle cells. It achieves this by inhibiting Ca2+ ions release from SR stores by antagonizing ryanodine receptors
owners hose dogs down with water. This is …
whole body wetting w water comb. w muscle massage
and blowing fans is commonly performed
administration of room temperature
rarely, whole body shaving is needed to facilitate cooling
cooling measures should be discontinued when
very effective
often results in a normal body temperature
Whole body wetting with water combined with muscle massage
IV fluids may be helpful
rectal temperature reaches 39.4°C (103°F) to prevent rebound hypothermia
If hypothermia occurs, warm water bottles or blankets may be necessary
DIC
Prolonged PT/PTT
< platelet count
> FDPs & D-dimers suggest DIC
GI mucosal sloughing and ulceration from:
breakdown of mucosal barrier may result in:
direct thermal damage
poor visceral perfusion
reperfusion
bacteremia or endotoxemia
consider antibiotics
Px: degree of compromise depends on the prior physical health of the dog and the degree and duration of the heat insult
Dogs w MODS or severe CNS disturbances have a more
guarded prognosis
However, many dogs with severe CNS disturbances, DIC, and other organ dysfunction live without any residual problems
Severe heat-induced illness is challenging to treat, but with aggressive medical therapy dogs may recover and do well
cats rarely develop heat stroke
