Thermoregulation

Question 1

Basal metabolic rate

Answer 1

determines rate of metabolism of nutrients and rate of skeletal muscle contraction; both metabolism and muscle contraction generate heat

Question 2

Heat retention mechaisms

Answer 2

Raising hairs (piloerection) – hairs trap warm air
▪ Vasoconstriction of blood vessels in skin – prevents loss from convection, conduction and radiation
▪ Behavioural responses (e.g., herding, huddling, nesting)
▪ Shivering

Question 3

Cooling mechanism

Answer 3

o Decreasing metabolic rate
o Heat in deep tissues is transferred to the skin via flow of blood from the core to the body surface. Once at the body surface, heat is lost by conduction, convection and radiation

Question 4

Normal temp of cat and dogs

Answer 4

38.5 +- 0.5(above 39.1 must be reported)

Question 5

Normal temp for cow

Answer 5

38.5+- 0.5

Question 6

Normal temp for horse

Answer 6

38.0+-0.5

Question 7

when is temp fatal

Answer 7

43 and above-rapidly fatal
28-dying

Question 8

Heat stress is

Answer 8

▪ 39.1 to 41.5 °C
▪ Lethargy, sweating, panting
▪ Decreased athletic performance
▪ Decreased production (milk, growth, breeding)
▪ Changes in hydration and electrolytes
o Increased temperature increases metabolic demand by muscle

Question 9

Treatment for heat stress

Answer 9

▪ Passive surface cooling (soak, shade, drink):
* Shade
* Proper ventilation
* Decrease ambient temperature
* Fans, misting, decrease density
* Water
o Prognosis is good if it does not progress to heat stroke

Question 10

Heat stroke is

Answer 10

o Core body temperature exceeds 41.5*C for a sustained period of time
o Any body temperature above 43 °C is critical and must respond NOW
o No accompanying signs of inflammation (in other words, this is not likely to be a true fever

Question 11

Pathology of heat stroke

Answer 11

▪ Intracellular proteins denature and mitochondria stop functioning. This leads to cell damage that is followed rapidly by cell death
▪ Sloughing of the intestinal mucosa occurs → seen as vomit and diarrhea; can lead to sepsis from intestinal bacteria
▪ Dehydration (from sweating, panting and increased evaporative losses)
▪ Respiratory alkalosis (from panting)
▪ Excessive peripheral vasodilation can lead to decreased BP and ischemia
▪ Blood also moves away from core to the body surfaces for cooling; core tissues may not be properly perfused
▪ Cardiac arrhythmias, disseminated intravascular coagulation (DIC is described in vascular conditions), muscle injury, CNS injury, hepatic injury can all occur (due to protein denaturation)
▪ When 2 or more of the organs shut down, this is referred to multi-organ dysfunction syndrome (MODS)

Question 12

Passive cooling

Answer 12

Cool room, shade
▪ Fans, ventilation, soak with tepid water
▪ Drink fluids (if patient is able to)

Question 13

What is the goal when cooling an animal

Answer 13

Goal is to decrease to 39.5 C within 30-45 min. Stop cooling at 39.5 °C provided risk factors have been controlled

Question 14

Active surface cooling

Answer 14

(If <43 °C)
▪ Apply cold packs to neck, foot pads, inguinal region and axilla’s - these are where the largest blood vessels are located
▪ Goal is cool blood as it moves through the largest blood vessels near the body surfaces

Question 15

Active core cooling

Answer 15

Indicated for critical heat stroke
▪ Chilled IV fluids
▪ Cool water enemas

Question 16

Mu-agonist induced hypothermia in cats

Answer 16

Uncommon to common
- Mu-agonists are the class of opioids that include morphine, hydromorphone, fentanyl
- Certain cats administered any of these mu-opioids may develop hyperthermia
- Diagnosis and Clinical Sign:
o Temperature does not drop as expected during general anesthetic
o Gradual increase in temperature

Question 17

Treatment for mu-agonist induced hyperthermia in cats and prognosis

Answer 17

Treatment
o Intervene at 41°C (usually happens within 30-90 min of giving the drug)
o Treat by reversing the opioid
▪ Mu-reversal drugs include buprenorphine, butorphanol, naloxone
- Prognosis is good is caught in time and treated with reversal agent
- Can be fatal if not caugh

Question 18

Malignant hyperthermia

Answer 18

Fatal hyperthermia triggered by exposure to inhalant general anesthetics (isoflurane and sevoflurane)
- Can happen in all species (including humans)
o Rare
o Most common in pigs (aka Porcine Stress Syndrome)
- Inherited defect in skeletal muscle metabolism; no effect unless triggered by exposure to gas anesthetic
o Mutation causes excessive Ca+ release by sarcoplasmic reticulum in muscle only when exposed to isoflurane or sevoflurane
o Excessive Ca+ causes muscles to contract and stay contracted
o Muscle activity generates heat
o Muscle also switch to anaerobic metabolism and this leads to metabolic acidosis
- Once triggered, temp increases 1-2 °C every 5 min (will rapidly exceed 43 °C)
- Treatment
o Stop anesthetic
o Start aggressive cooling (e.g., dump ice into open abdomen); muscle relaxants; aggressive CV support

Question 19

Hypothermia due to increased heat loss risks

Answer 19

▪ Heat production is normal
▪ The problem is usually related to environmental conditions
▪ Risks include the following:
* Cold environmental temperature
* Wet
* Low BCS (lack of subcutaneous fat)
* Neonates – heat regulation is normal but less developed than in adults; increased body surface area for increased heat loss; low body fat. Example is kittens and foals born in snow
* Small animals - due to increased body surface area

Question 20

Hypothermia due to lack of heat production

Answer 20

▪ Can occur with severe illness such as shock
▪ Brain trauma
▪ Consistent adverse effect of GENERAL ANESTHESIA
* #1 cause of hypothermia seen in a hospital setting; too frequent
* Highest risk: <10 kg, pediatrics, geriatrics, open abdominal surgery, trauma, too long a procedure, cold gasses; lack of warming
* All general anesthetic agents cause vasodilation (blood vessels dilate
and encourage cooling), decreased basal metabolic rate, stop shivering; depress hypothalamus function

Question 21

Mild hypothermia

Answer 21

34-37*C
Lethargy, depression, shivering
Loss of suckle response

Question 22

Moderate hypothermia

Answer 22

28-33*C
Loss of physiological warming response
Uncoordinated to unconscious
Decreased metabolism
Decreased HR and CO
Decreased muscle function (affects resp)

Question 23

Severe hypothermia

Answer 23

<28*C
Collapse, uncoscious, coma
Death

Question 24

Prevention of hypothermia

Answer 24

o Appropriate shelter for birthing and neonatal care
o Avoid wetness in cold temps
o Minimize anesthetic times, warm IV fluids during prolonged GA, warm ambient temperature; monitor temperature q15 min while under GA; provide proper patient support in the pre-/intra-/post-operative periods

Question 25

Treatment of hypothermia

Answer 25

1. Maintain heat using passive surface methods (see below)
2. Support vital functions – O2, anti-arrhythmic drugs, warm IV fluids
3. LASTLY, active warming methods to restore body temp
   ▪ Start with warm fluids given IV > enema > inguinal/axilla/neck
   ▪ Same as with cooling, start with the inside out; if excess heat is applied to the surface this will cause vasodilation of blood vessels on the surface and exacerbate heat loss
   * Stop warming at 37 °C (rectal temp

Question 26

Passive surface warming

Answer 26

Goal: Maintain heat and prevents more loss
▪ How to: Get out of the cold and wet; transfer to warm shelter or warm environment; dry off; blankets, foil wrap, bubble wrap

Question 27

Active surface warming

Answer 27

Goal: Provide mild heat to the body surface; the body transfers this heat to the core
▪ How to: Warm water bottles to axilla’s, inguinal region, neck (where largest blood vessels exist near the body surface) to warm the blood as it flows past; forced air blankets (Bair huggers)
▪ Warning: If too hot will make things worse; aim for normal body temperature range at the skin surface (warmer than ambient temperature to have an effect

Question 28

Active core warming

Answer 28

Goal: Provide large amounts of heat to the body core
▪ Breathe in warmed air, warm IV fluids, warm enema

Question 29

What to do after starting the warming process

Answer 29

Monitor every 15 minutes during re-warming
- Continue monitoring after temperature is restored in case of inability to maintain temp
o Cats have an especially difficult time maintaining body temperature after recovering from hypothermia

Question 30

After drop phenomenon

Answer 30

o Occurs if patient reaches 37 °C, but active heating sources not removed
o Patient becomes too warm in the core → to cool down again, blood from the periphery (which is always cooler) will move to the core, and cause a sudden decrease in the core temperature despite all your efforts
o Sudden decrease in core temperature can precipitate heart and CNS dysfunction

Question 31

Rewarming shock

Answer 31

o Occurs if there is external warming without core warming at the same time
o Causes sudden vasodilation of the blood vessels in the skin → blood moves to skins surface to fill blood vessel space → this draws blood away from the vital organs and the patient could go into shock
o Note: This is different from simply causing the body to lose even more heat

Question 32

Frostbite risk factors

Answer 32

Cold, wet, windchill
o Neonates (<48 hours of age)
o Really old or really ill
o If there is already poor perfusion of extremities (cattle that lay in the snow and body weight compresses blood vessels in the dependent muscle; vascular disease in diabetics)

Question 33

Pathology of frostbite

Answer 33

o Ice crystals and expansion of frozen water cause permanent tissue damage
o Lack of blood flow (due to a combination of damage to blood vessels and vasoconstriction) mean increased risk of tissue necrosis
NECROSIS – dying/dead cells or tissue
o Increased risk of bacterial infection upon thawing due to damage to protective skin layer; lack of movement of immune cells into area; certain bacteria (i.e., anaerobic bacteria such as Clostridia also like to colonize necrotic tissue

Question 34

Clinical signs of frostbite

Answer 34

o Skin is hard, cold, pale; there is loss of sensation/pain
o Sound solid (“knocking sound”) when tapped

Question 35

Treatment of frostbite

Answer 35

1. Take out of cold
2. SLOW PASSIVE SURFACE REWARMING (passive surface is usually sufficient if there is no drop in body temperature)
   ▪ NEVER rub
   ▪ Move as little as possible
   ▪ NEVER immerse in hot water
3. Protect damaged area (E-collar, light dressing)
4. Support core organs (IV fluids)
5. Anti-inflammatories, pain control, antibiotics
6. NEVER thaw and refreeze, better to leave it frozen

Question 36

Frostbite prognosis

Answer 36

o Only know after the tissue thaws
▪ When skin thaws, it will be red, swollen painful.
▪ If damage is too severe and tissue becomes necrotic, it will be purple/black with red margins and start to slough.
▪ Necrotic tissue has very high risk of bacterial infection (gangrene)
o May regain full function or require amputation/euthanasia