8.1 TTM + Cooling

Question 1

a) What are the cerebral physiological benefits of induced hypothermia following successful resuscitation from cardiac arrest? (25%)

Answer 1

1. reduction in CMRO2 - reduces metabolic demand on brain
2. In VF arrests proven survival benefit
3. VF arrest proven morbidity benefit and greater return to function

Question 2

b) How can a patient be cooled in these circumstances? (20%)

)

Answer 2

1. Cold fluid infusions
   NaCl
2. Ice packs
   placed around body
3. Bladder irrigation with cold saline
4. Cooling blankets
5. Parcetamol for fever avoidance

Question 3

c) What adverse effects may occur due to the use of induced hypothermia? (35%)

Answer 3

1. Increased risk of cardiac arrythmias
2. Prolonged ability to neuroprognisticate patients
3. Shivering may increase metabolic demand
4. Requires deep sedation and often paralysis
5. Clotting abnormalities at extremes of temp
6. increased risk of infection

Question 4

d) In what other nonsurgical clinical scenarios may the use of induced hypothermia be beneficial? (20%)

Answer 4

1. Rx of Malignant hyperpyrexia
2. Proposed benefit in TBI but not proven
3. Deep circulatory arrest

Question 5

a) What are the cerebral
physiological benefits of (induced
hypothermia-x) targeted temperature
management following successful
resuscitation from cardiac arrest?
(25%)

Answer 5

The NICE guidance from 2011, referenced below, advised cooling to 32–34°C for patients who had suffered cardiac arrest followed by return of spontaneous rhythm. Later that year, this question featured in the final exam.

However, subsequent research has found no improvement in outcome when targeting 33°C compared with targeting 36°C, yet hypothermia is associated with significant complications.

Therefore, temperature control following cardiac arrest is now called targeted temperature management and aims for 36°C in the hope of gaining the benefits of temperature control and avoidance of pyrexia (common following resuscitation from cardiac arrest) with a lower burden of complications.

Question 6

a) What are the cerebral
physiological benefits of (induced
hypothermia-x) targeted temperature
management following successful
resuscitation from cardiac arrest?
(25%)

Answer 6

Targeted temperature management avoids the deleterious effects of pyrexia,
which occurs commonly after
resuscitation from cardiac arrest.

Reduction of temperature to 36°C has the following effects:

1. > > Reduced cerebral metabolic rate for oxygen (CMRO2), resulting in reduced oxygen and glucose consumption.
2. > > Suppression of release of oxygen free radicals during reperfusion after cardiac arrest.
3. > > Suppression of destructive neuroexcitotoxic cascade (glutamate release, receptor activation, leading to intracellular calcium overload and cell
   death) .
4. > > Reduction of expression of pro-apoptotic signals.
5. > > Reduction of cerebral oedema associated with reperfusion.

Question 7

b) How can a patient be cooled in

these circumstances? (20%)

Answer 7

Surface cooling:
» Ice packs.
» Surface heat-exchange devices.
» Surface cooling helmet.

Internal cooling:
» Endovascular cooling devices.
» Infusion of cold fluids.

Question 8

What adverse effects may
occur due to the use of induced
hypothermia? (35%)

B C E

Answer 8

This is no longer relevant to this situation now that patients are cooled to only 36°C. However, the knowledge of the systemic risks of hypothermia
in the perioperative period was tested in a paper in 2010 and so I list them here for you to learn:

Resp:
» Increased risk of pneumonia.

Cardiovascular:
» Initially catecholamine release, increased oxygen demand, increased cardiac output.

> > Arrhythmias.

> > Shivering increases oxygen demand.

Endocrine:
» Reduced insulin release with increased insulin resistance resulting in
elevated blood glucose.

Question 9

What adverse effects may
occur due to the use of induced
hypothermia? (35%)

G H

Answer 9

Gastrointestinal:
» Reduced motility compromising enteral nutrition.
» Rarely, pancreatitis.

Haematological:

> > Reduced platelet number (sequestered in spleen and liver) and function results in prolonged bleeding time.

> > Decreased clotting factor function.

Question 10

What adverse effects may
occur due to the use of induced
hypothermia? (35%)

I K M

Answer 10

Immune, infection:
» Impaired immune function, overall increased risk of sepsis.

Renal:
» Diuresis and loss of electrolytes resulting in risk of hypovolaemia and effects of electrolyte imbalance such as arrhythmia.

Metabolic:
» Lactic acidosis.
» Hypoxic perinatal brain injury.

Question 11

d) In what other nonsurgical
clinical scenarios may the use
of induced hypothermia be
beneficial? (20%)

Answer 11

Newborn hypoxic–ischaemic encephalopathy

Traumatic head injuries?