Lecture 7: Thermoregulation & Postoperative Care

What is responsible for the sensation of temperature?

spinothalamic tract transmits temp signals to CNS → hypothalamus → efferent pathway ends at peripheral alpha motor neurons → blood vessel tone, shivering or sweating

What are the four heat loss mechanisms?

1. Radiation: loss of heat via electromagnetic waves

2. Convection: process of losing heat through the movement of air or water molecules across the skin

3. Conduction: loss of heat to objects directly in contact with body

4. Evaporation: loss of heat through conversion of water to gas (i.e. moisture from skin and lungs)

What type of heat are a body warmed by absorbing rays of sunshine; wood stove warming a room; microwave uses electromagnetic radiation to transfer heat to food an example of?

radiation

What type of heat is heat exchanged between the body and ambient air or water in which it moves; Examples include a fan blowing on you, wind-chill factor, swimming in a cold pool or moving body of water?

convection

What type of heat is a seat staying warm after you have sat on it; cold surgery table cooling a patient down; holding cold water bottle to your head?

conduction

What type of heat is passively through respiration (air breathed out has moisture) and active through

sweating (body creates a layer of water on the skin to cool down)?

evaporation

What body temperatures are associated with mild, moderate, and severe hypothermia?

mild: 89.6-98.6

moderate: 82.4-89.6

severe: < 82.4

What physiologic changes are associated with mild, moderate, and severe hypothermia?

mild: Increased basal MR and O2 consumption; vasoconstriction; SNS activation

moderate: Slowing of HR & breathing, low BP

severe: Further slowing of HR, development of arrhythmias prior to stopping. No PLR.

What clinical signs are associated with mild, moderate, and severe hypothermia?

mild: Heat-seeking behavior, shivering, tachycardia, tachypnea, diuresis

moderate: Decreasing conscious state, No longer shivering

severe: No longer conscious, Rigid muscles, Pulses and respiration difficult to detect

What are passive strategies to warm anesthetized patients?

• blankets/towels

• wrap extremities

What are active rewarming strategies for anesthetized patients?

• Forced-air blankets

• Circulating warm water blankets

• Resistive polymer electric heating (ex. HotDog Patient Warming System)

• Humidifiers placed in inspiratory limb of breathing system

• IVF warmers

• Warm fluids to lavage in abdominal cavity

• Prewarming patient’s skin and peripheral tissue (i.e. place in incubator)

True or false: it is encouraged to use electric heating pads/blankets for anesthetized or recovering patients.

FALSE it is not safe

What are the 7 causes of hyperthermia?

1. Heat stroke (i.e. environmental heat and/or humidity)

2. Respiratory obstruction/inability to pant

3. Exercise induced

4. Histamine release

5. Iatrogenic (i.e. drug induced or overzealous heating

of a patient)

6. Prolonged seizure activity or muscle activity

7. Malignant hyperthermia (i.e. pathologic)

From a clinical standpoint, pyrexia and hyperthermia are approached differently. How is pyrexia usually treated?

• cooling patient may be counter-productive → body expend energy to get body back to temp to fight pathogens

• avoid antibiotics until origin is known (sepsis is exception)

• avoid steroids if possible

• acetaminophen can be used in DOGS only but caution in liver dysfunction

From a clinical standpoint, pyrexia and hyperthermia are approached differently. How is hyperthermia usually treated?

• requires active measures: sedation, anxiolysis, muscle relaxants

• no ice packs (causes vasoconstriction & inhibits dissipation of heat from core body)

• do not over cool patient - stop around 104 to avoid rebound hypothermia

Why should aggressive methods of cooling a patient be used with caution?

they can cause peripheral vasoconstriction and can cause hypothermia

What are 1st line strategies to actively cool a hyperthermic patient?

• O2

• room temp IVF

• fan

• water applied to skin

• shaving fur on belly

What drugs is hyperthermia commonly associated with in cats?

opioids (hydromorphone)

True or false: hyperthermia in cats is usually seen in the first 5 hours of recovery and if patient is quiet and comfortable, will resolve and is not clinically significant.

true

How does hypothermia and hyperthermia affect the immune system?

hypothermia: Decreased function (chemotaxis, phagocytosis, antibody production, ect); delayed wound healing

hyperthermia: Inflammatory response, vascular stasis, extravasation, edema

How does hypothermia and hyperthermia affect the hematopoietic system?

hypothermia: Hemoconcentration and increased viscosity; left shift of oxyHb curve, decreased RBC deformability, coag abnormalities, DIC

hyperthermia: DIC, hemorrhage

How does hypothermia and hyperthermia affect the CV system?

hypothermia: Reduced CO, decreased contractility, arrhythmias, vasoconstriction; cardiac drugs less effective

hyperthermia: Tachycardia, hypotension, cardiac failure due to high output

How does hypothermia and hyperthermia affect the respiratory system?

hypothermia: Falsely increased PaO2; decreased RR

hyperthermia: Increase in ventilation

How does hypothermia and hyperthermia affect the renal system?

hypothermia: Decreased renal tubular function

hyperthermia: Acute tubular necrosis, low urine output, rhabdomyolysis, renal failure

How does hypothermia and hyperthermia affect the GI system?

hypothermia: Elevated serum amylase

hyperthermia: Intestinal ischemia and infarction, translocation of bacteria from gut, endotoxemia

How does hypothermia and hyperthermia affect the hepatic system?

hypothermia: Reduced hepatic function (altered enzyme activity) can prolong duration and effects of drugs

hyperthermia: Production of PGE2, failure of function

How does hypothermia and hyperthermia affect the metabolic system?

hypothermia: Falsely decreased pH, decreased adrenal activity, hyperkalemia, delayed wound healing

hyperthermia: Severe hypoglycemia, depletion of glycogen stores, electrolyte imbalance

How does hypothermia and hyperthermia affect the neurologic system?

hypothermia: Stupor progressing to coma, absent motor and reflex functions

hyperthermia: Neurologic dysfunction -delirium, coma, seizures

What is the Celsius to Fahrenheit conversion?

(C temp x 1.8) + 32

What are the post-op steps after surgery is complete, before extubating?

1. remove drapes, instruments, & non-essential monitors from patient, but leave ETCO2 ± SpO2 & palpate pulses (or use stethoscope)

2. patient placed in lateral or sternal recumbency (sternal if brachycephalic)

3. then, inhalant turned OFF, empty reservoir bag into scavenging system, then turn O2 flow rate up to recovery rates

4. continuous monitoring until extubated and alert

What are the post-op steps after patient is extubated?

• assess for mentation appropriateness and pain

• monitor rectal temp q 14-30 min until >98 & alert

• monitor vital signs

• remove IV catheter if appropriate & consider E-collar

What information should be included in discharge instructions?

• What behaviors to expect, Pain? Anxiety?

• Restrict activity and/or limit areas of house

• Recheck date; any bandages to monitor/change

• When to offer food and water and how much

• When to start any meds and should they be offered with food

• Signs they should monitor their pet for and when to call if concerned (Provide a number for clients to call after-hours)

What should postoperative care treatment orders include for hospitalized patients?

• vitals (usually q hour for the first few hours after anesthesia, then q 4-6 hr)

• serial pain scoring

• body weight (q 12 hr)

• urine and feces output

• hydration status

• feeding and water instructions

• IV fluids, medications, nursing care instructions

• exercise or physical therapy

What is considered a prolonged recovery?

Excessive time from discontinuation of inhalant anesthesia and the patient has not been extubated (~30-45 minutes)

What is considered a prolonged recovery in horses?

Prolonged time to standing in horses (~ 1-2 hr)

What steps should be taken if the patient has a prolonged recovery?

• check vitals (esp. temp), actively warm patient if needed

• check electrolytes and BG, treat as needed

• consider reversal of certain drugs