139 Heat stroke Flashcards
What are the major body systems affected by HS?
cardiovascular, central nervous, gastrointestinal, renal, and coagulation systems
What are clinical signs & findings that lead to a worse prognosis?
hypoglycemia, decreased cholesterol level, increased bilirubin concentration, decreased albumin level, ventricular arrhythmias, increased creatinine values, longer delay from incident to treatment, obesity, seizures, prolonged prothrombin time and activated partial thromboplastin time, disseminated intravascular coagulation, and increased number of nucleated red blood cells
Define HS
“hyperthermia associated with a systemic inflammatory response leading to a syndrome of multiorgan dysfunction in which encephalopathy predominates.”
What are the four mechanism of heat dissipation?
convection, conduction, radiation, and evaporation. In dogs, under normal environmental con
ditions,
more than 70% of total body heat is dissipated
through radiation and convection
Evaporation: As
environmental temperatures increase and approach body
temperature, evaporation, primarily through panting,
becomes more important for maintaining normothermia. The nasal turbinates provide a large surface area for
water loss from the moist mucous membranes, and play
an important role in heat dissipation. Hypersalivation
increases the evaporative efficiency, although high environmental
temperatures and increased humidity (>35%)
will decrease its effectiveness; when humidity is >80%, this
cooling measure will be negated
From which core temperature is it considered as heat stroke?
41°C (105.8 °F) with CNS dysfunction
What are the most common heat loads experienced by dogs?
Warm, humid environement and exercise
What factors can diminish the respiratory evaporative heat loss ability (environmental and related to anatomy)?
Humide, confinement in close space with poor ventilation, obstructive upper respiratory tract abnormalities (e.g., brachycephalic conformation, laryngeal paralysis, airway masses, or collapsing trachea), heat stress, obesity, breed (brachiocephalic, golden
and Labrador Retrievers), body weight (>15 kg), high
environmental temperature and humidity, and lack of
acclimation and fitness
What are 3 protective mechanisms happening in the body when there is increased body heat?
thermoregulation, an acute-phase response, and increased expression of intracellular heat shock proteins.
What is the role of heat shock proteins?
The heat shock proteins protect the cell and the body against further heat insults and prevent denaturation of intracellular proteins. They also help to regulate the baroreceptor response during heat stress, thus preventing hypotension and conferring cardiovascular protection. Heat stroke results from a failure of thermoregulation followed by an exaggerated acute-phase response and alteration of heat shock proteins.
What happens to the GI tract during heat stroke?
Additionally, absorption of endotoxin from the gastrointestinal (GI) tract may fuel the inflammatory response because intestinal mucosal permeability is increased during heat stress. It has been noted that many of the mediators involved in heat stroke are the same mediators associated with sepsis and the systemic inflammatory response syndrome.
What CBC abnormality is associated with worse prognosis?
The most common complete blood count abnormality reported is an increased number of NRBCs; as noted earlier, this is associated with a worse prognosis. In one canine heat stroke study, a value of 18 or more NRBCs per 100 leukocytes at presentation had a sensitivity and specificity of 91% and 88%, respectively, for predicting death. The NRBC level typically decreases rapidly over the first 24 hours. They
most likely occur secondary to heat-induced damage to
the bone marrow.This phenomenon can be
attributed to thermal lesions within the bone marrow,
leading to blood–bone marrow barrier injury and subsequent
release of nRBCs to the peripheral circulation.
An alternative hypothesis might be that bone marrow
release of nRBCs to the peripheral circulation in canine
heat stroke is mediated via the actions of cytokines.
List some cooling techniques
External conduction cooling techniques: application of ice packs over major vessels, tap water immersion, ice water immersion, and use of cooling blankets.
Use of fan
Massage muscles
IVF
What techniques are controversial and why?
- ice water baths may be uncomfortable and produce peripheral vasoconstriction and thus diminish heat dissipation overall
- Whole body alcohol bathing should be avoided because noxious to the animal and may present a significant fire hazard should defibrillation be required in dogs that experience cardiac arrest.
- wetting the footpads with alcohol seems like an ineffective cooling measure given the small surface area involved
- Internal conduction techniques include iced gastric lavage, iced peritoneal lavage, and cold water enemas, although the latter may interfere with rectal temperature monitoring. These techniques are invasive and can result in serious complications (aspiration pneumonia, septic peritonitis)
What is the mortality rate in dogs suffering HS?
40-50%
