Thermoregulation & Postoperative Care Lecture Notes PDF

Thermoregulation & Postoperative care Dr. Lisa Ebner CVM 746  Learning Objectives 1. List and describe the 4 mechanisms of heat loss and which ones contribute the most to heat loss in veterinary patients. 2. List potential causes of hyperthermia or hy...

Thermoregulation & Postoperative care Dr. Lisa Ebner CVM 746  Learning Objectives 1. List and describe the 4 mechanisms of heat loss and which ones contribute the most to heat loss in veterinary patients. 2. List potential causes of hyperthermia or hypothermia in an anesthetized patient. 3. Determine what body temperatures under anesthesia would make you concerned about hypothermia or hyperthermia. 4. Describe the harmful effects on different systems in the body that both hypothermia and hyperthermia can have. 5. List ways that a patient can be safely warmed or cooled when indicated. 6. Describe the basic steps/end-goals of recovering a patient from general anesthesia  What is thermoregulation? Ability of an organism to maintain body temperature within a certain range (± 0.2◦C), even when surrounding temperatures vary Normally around 100 to 102.5◦F in dogs and cats Most domestic mammals – homeothermic Reptiles, amphibians, some fish - poikilothermic Additional fluctuations due to time of day, time of year, hormones, and activity level Core body temp often 2-4 ◦C higher than skin temp Body systems involved – CNS, CV, respiratory, musculoskeletal, and integument Abnormal body temp in awake animal  metabolic dysfunction Abnormal body temp in anesthetized animal  fluid or drug-related; environmental Sensation of temperature Central regulation Spinothalamic tract transmits Efferent pathway ends temperature at α motor neurons: signals to CNS Blood vessel tone Shivering or sweating Image: http://psychologyinfilm.weebly.com/brain-structure.html  Four heat loss mechanisms: *Radiation- loss of heat via electromagnetic waves *Convection- process of losing heat through the movement of air or water molecules across the skin Conduction- loss of heat to objects directly in contact with body Evaporation- loss of heat through conversion of water to gas (i.e. moisture from Image: http://www.onlinesurgicals.com/store/hypothermia-prevention skin and lungs) 02flowral  Radiation – body warmed by absorbing rays of sunshine and the body loses heat by thermal radiation; wood stove warming a room; microwave uses electromagnetic radiation to transfer heat to food mailost Convection – heat exchanged between the body and ambient air or water in which is moves. Examples include a fan blowing on you, wind-chill Examples factor, swimming in a cold pool or moving body of water Conduction – a seat staying warm after you have sat on it; cold surgery table cooling a patient down; holding cold water bottle to your head Evaporation – passively through respiration (air breathed out has moisture) and active through sweating (body creates a layer of water on the skin to cool down)  Physics review: Radiation is the transfer of heat via electromagnetic waves through airspace Usually occurs when ambient temperature is below 68 degrees F Most of the electromagnetic radiation that comes to the earth from the sun is invisible. Only a small portion comes as visible light. Light is made of waves of different frequencies https://www.sciencedirect.com/topics/neuroscience/electromagnetic-radiation  Hypothermia What body temperature defines it? Common anesthetic complication, especially with increased duration of anesthesia. Why? What factors are related to the rate of heat loss? Extentsize of p of hypothermia can be mild, moderate or severe. What physiologic changes and clinical signs are as associated with each? Extent of Temperature range Physiologic changes Clinical signs hypothermia Mild 89.6-98.6 F Increased basal MR and O2 consumption; vasoconstriction; Heat-seeking behavior, shivering, tachycardia, SNS activation tachypnea, diuresis Moderate 82.4-89.6 F Slowing of HR & breathing, low BP Decreasing conscious state crash No longer shivering Severe