Thermoregulation

Question 1

What are the phases of heat loss and how are they

characterized?

Answer 1

Core body temperature usually decreases 1-2 degrees Celsius
during the first hour of anesthesia (Phase I), then gradually
decreases over the next 3-4 hours (Phase II), then a consistent,
steady-state or equilibrium temperature is reached (Phase III).
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 1184.

Question 2

What temperature defines hypothermia?

Answer 2

Anything less than 36 degrees Celsius.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 321.

Question 3

What are the four routes of heat loss? Name them in

the order from greatest degree of heat loss to least.

Answer 3

Radiation, convection, conduction, and evaporation
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222

Question 4

Explain radiant heat loss. Where does it occur to the

greatest degree in the human body?

Answer 4

Radiant heat loss is the transfer of electromagnetic radiation
from the body to the cooler ambient environment. Blood carries
heat from the body’s core to the skin where it is emitted as
infrared radiation. It occurs to the highest degree in the head
because of the high percentage of blood flow it receives.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222.

Question 5

How does radiant heat loss occur?

Answer 5

Radiant heat loss is the transfer of heat from the body into the
cooler operating room.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222

Question 6

What is evaporative heat loss?

Answer 6

Evaporative heat loss occurs when moisture from the skin,
exposed organs, and the respiratory tract turns from the liquid to
gas phase. This process requires energy and the majority of
the energy comes from our bodies. As a result of the loss of
energy, our body loses heat as well.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222.

Question 7

How does evaporative heat loss occur?

Answer 7

Evaporative heat loss occurs when liquids on the surface of the
body evaporate into the air.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222-223.

Question 8

What is conductive heat loss?

Answer 8

Conduction is the transfer of heat energy from one object to
another through physical contact. This is the method of heat
loss that occurs when a patient is placed on a cold operating
room table. Heat from the patient is lost to the colder table
surface.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222.

Question 9

What is convective heat loss?

Answer 9

Convection is the generation of air currents by heat. As heat is
emitted, it rises in a current and is replaced by cooler air.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222.

Question 10

How do convective and conductive heat loss occur?

Answer 10

Convective heat loss occurs as cooler air moves across the
body’s surface and conductive heat loss occurs when the body
is in contact with a cooler surface such as an operating room
table.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222.

Question 11

What type of heat loss accounts for most of the heat

lost during surgery?

Answer 11

Radiant heat loss accounts for most of the heat lost in a surgical
patient.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 222

Question 12

What temperature defines hyperthermia?

Answer 12

Anything exceeding 38 degrees Celsius.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 321

Question 13

Does regional anesthesia affect the

thermoregulatory mechanism?

Answer 13

Yes, by blocking the thermoregulatory afferent and efferent
nerve fibers, regional anesthesia interferes with sweating,
vasoconstriction, and shivering responses.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 1508.

Question 14

What nerve fibers mediate the sweat response?

Answer 14

Cholinergic sympathetic fibers
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 1507.

Question 15

Why do patients describe a warming sensation on

injection of neuraxial local anesthetics?

Answer 15

The blockade of the thermoregulatory afferent nerve fibers
causes the hypothalamus to incorrectly interpret the peripheral
temperature as high.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 1508.

Question 16

What are four drugs that have been used

successfully to prevent shivering?

Answer 16

Demerol, clonidine, ketanserin, and dexmedetomidine
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 1509.

Question 17

What temperature change stimulates the sweat

response?

Answer 17

An increase in temperature of 0.9 degrees F (0.5 degrees C)
produces a 7-fold increase in the sweat rate.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 1507