Controlled Hypothermia

Question 1

What is controlled hypothermia and why is it used?

Answer 1

Controlled hypothermia is a reduction in core body temperature
that is induced to decrease the cerebral metabolic rate, which
provides protection to the brain during periods of ischemia.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 1007.

Question 2

What is the difference between mild and profound

hypothermia?

Answer 2

Mild hypothermia is considered to be a reduction in core body
temperature to 33-35 degrees Celsius. Profound hypothermia
is considered to be as low or even lower than 20 degrees
Celsius.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 1007.

Question 3

Is mild hypothermia of benefit in surgical patients?

Answer 3

Although core temperatures as low as 20 degrees Celsius have
been used to successfully provide neurologic protection during
cases of total circulatory arrest, even mild hypothermia (33-35
degrees Celsius) demonstrates some potential for neurologic
protection by maintaining ATP levels at normal even when
oxygen levels are at half normal. Perhaps more importantly,
there is a great deal of research that demonstrates that
hyperthermia is extremely deleterious for patients who have
suffered a cerebral infarct, subarachnoid hemorrhage, or
cardiac arrest. Because of this information, many clinicians
prefer to induce mild hypothermia simply to avoid inadvertant
hyperthermia.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 1007-1008.

Question 4

What are the disadvantages of using profound

hypothermia?

Answer 4

Cardiopulmonary bypass is needed during the cooling and
warming periods and hypothermia-induced coagulopathy can
present concerns for post-operative bleeding.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 1007.

Question 5

What is the typical application of profound

hypothermia?

Answer 5

Some cardiac and cerebral procedures such as aneurysm
repair can be performed under complete circulatory arrest using
profound hypothermia. When the body temperature is less than
20 degrees Celsius, circulatory arrest can be tolerated for up to
about 30 minutes. Profound hypothermia provides greater
protection against cerebral ischemia than oxygen administration
or anesthetic agents.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 1007.