Lecture 7- Thermoregulation & Postop Care

What is thermoregulation?

Ability to maintain body temperature within ±0.2°C despite environmental changes.

What is normal body temperature range for most domestic mammals?

99-103°F.

What types of animals are homeothermic vs. poikilothermic?

Homeothermic: domestic mammals; Poikilothermic: reptiles, amphibians, most fish.

How much higher is core temperature compared to skin temperature?

2-4°C higher.

What body systems regulate temperature?

CNS, cardiovascular, respiratory, musculoskeletal, integument.

What does abnormal temperature in an awake animal usually indicate?

Metabolic dysfunction or illness.

What does abnormal temperature in an anesthetized animal usually indicate?

Fluid/drug effects or environmental causes.

What pathway transmits temperature sensation to the CNS?

Spinothalamic tract.

What are the four mechanisms of heat loss?

Radiation, convection, conduction, evaporation.

Which heat loss mechanisms contribute most to hypothermia under anesthesia?

Radiation and convection.

Define radiation heat loss.

Heat loss via electromagnetic waves to cooler surroundings.

Define convection heat loss.

Heat loss via movement of air or water across skin.

Define conduction heat loss.

Heat loss to objects in direct contact with the body.

Define evaporation heat loss.

Heat loss via conversion of water to vapor from skin and lungs.

At what ambient temperature does radiation heat loss occur most?

Below 68°F.

What is the definition of hypothermia?

Body temperature below normal physiologic range under anesthesia.

What are the temperature ranges for mild, moderate, and severe hypothermia?

Mild: 89.6-98.6°F; Moderate: 82.4-89.6°F; Severe: <82.4°F.

What physiologic changes occur in mild hypothermia?

Increased metabolic rate, O₂ consumption, vasoconstriction, SNS activation.

What clinical signs occur in mild hypothermia?

Shivering, tachycardia, tachypnea, diuresis, heat‑seeking.

What physiologic changes occur in moderate hypothermia?

Bradycardia, slowed breathing, hypotension.

What clinical signs occur in moderate hypothermia?

Decreased consciousness, no longer shivering.

What physiologic changes occur in severe hypothermia?

Severe bradycardia, arrhythmias, absent PLR.

What clinical signs occur in severe hypothermia?

Unconsciousness, rigid muscles, difficult‑to‑detect pulses/respiration.

What are passive rewarming methods?

Blankets, towels, wrapping extremities.

What are active rewarming methods?

Forced‑air blankets, circulating warm water blankets, resistive polymer heating, humidifiers, warmed IV fluids, warm lavage fluids, prewarming skin.

Why are electric heating pads unsafe for anesthetized patients?

Risk of burns due to impaired sensation and inability to move.

What defines hyperthermia?

Body temperature above normal physiologic range under anesthesia.

What differentiates pyrexia from hyperthermia?

Pyrexia = cytokine‑mediated set‑point increase; Hyperthermia = failure of thermoregulation.

List causes of hyperthermia.

Heat stroke, respiratory obstruction, exercise, histamine release, iatrogenic heating/drugs, seizures, malignant hyperthermia.

Why should fever not be aggressively cooled?

Body will expend energy to return to febrile set‑point; cooling may worsen condition.

What medications should be avoided in fever unless necessary?

Antibiotics (until diagnosis), steroids.

What drug can be used for fever in dogs only?

Acetaminophen (avoid in liver dysfunction).

How is hyperthermia treated?

Sedation, anxiolysis, muscle relaxation, active cooling (without ice packs), stop cooling at ~104°F.

Why are ice packs contraindicated in hyperthermia?

Cause vasoconstriction → impaired heat dissipation.

What are first‑line cooling strategies?

O₂, room‑temperature IV fluids, fan, water on skin, shave belly.

What cooling methods should be avoided?

Cold water enemas, gastric lavage (aspiration risk).

How often should temperature be monitored during cooling?

Every 5 minutes.

What is post‑anesthetic hyperthermia in cats associated with?

Opioids, especially hydromorphone.

When does post‑anesthetic hyperthermia in cats typically occur?

Within first 5 hours of recovery.

How should post‑anesthetic hyperthermia in cats be managed?

Treat agitation; if quiet/comfortable, usually self‑resolving.

What harmful immune effects occur with hypothermia?

Decreased chemotaxis, phagocytosis, antibody production; delayed wound healing.

What harmful immune effects occur with hyperthermia?

Inflammation, vascular stasis, edema.

What cardiovascular effects occur with hypothermia?

Reduced CO, decreased contractility, arrhythmias, vasoconstriction.

What cardiovascular effects occur with hyperthermia?

Tachycardia, hypotension, high‑output cardiac failure.

What renal effects occur with hypothermia?

Decreased tubular function.

What renal effects occur with hyperthermia?

Acute tubular necrosis, oliguria, rhabdomyolysis, renal failure.

What neurologic effects occur with hypothermia?

Stupor → coma; absent reflexes.

What neurologic effects occur with hyperthermia?

Delirium, coma, seizures.

How do you convert Celsius to Fahrenheit?

(C × 1.8) + 32.

What are the first steps after surgery ends?

Remove drapes/instruments; leave ETCO₂ ± SpO₂; palpate pulses; position patient.

What is the correct sequence for turning off inhalant anesthesia?

Turn off vaporizer → empty reservoir bag → increase O₂ flow → deliver O₂ 3-5 minutes.

What should be monitored during recovery?

Mentation, pain, temperature, HR, RR, MM, CRT, quality of breathing.

When should you extubate?

When patient is swallowing, conscious enough to protect airway.

What should be done before pulling the ETT?

Clear oropharynx, deflate cuff, ensure adequate ventilation.

How often should temperature be checked post‑extubation?

Every 15-30 minutes until >98°F and alert.

What should be done before leaving a hospitalized patient?

Complete treatment plan, document orders, ensure staff understands plan.

What should discharge instructions include?

Expected behaviors, pain/anxiety, activity restriction, recheck date, bandage care, feeding instructions, medication timing, warning signs, after‑hours contact.

What parameters should be monitored in hospitalized postoperative patients?

Vitals, pain score, body weight, urine/feces output, hydration, feeding/water intake.

What is maintenance IV fluid rate for dogs?

40-60 mL/kg/day.

What is the maintenance fluid rate for a 20 kg dog?

800-1200 mL/day → ~33-50 mL/hr.

What is considered a prolonged recovery?

>30-45 minutes without extubation; >1-2 hours to stand in horses.

What should be checked in prolonged recovery?

Vitals, temperature, perfusion, drug effects, hypothermia, hypoglycemia, ventilation.