Deep Hypothermic Circulatory Arrest

Question 1

What are the temperatures of the hypothermia classifications in aortic arch surgery (profound, deep, moderate, mild)?

Answer 1

Profound <14C
Deep 14.1-20C
Moderate 20.1-28C
Mild 28.1-34C

Question 2

What is pH stat vs alpha stat?

Answer 2

pH stat - maintains a normal pH at hypothermia by adding CO2. This causes cerebral vasodilation and eliminates the autoregulatory capacity of the cerebral microvasculature. pH stat is better in pediatrics. pH stat may increase embolic injury.

alpha stat - allows the blood to become more alkaline during hypothermia. This causes a left shift in the oxyhemoglobin dissociation curve leading to less oxygen released to tissue

Question 3

What is the safe duration for HCA at different temperatures?

Answer 3

Temp (C)- Cerebral metabolic rate (%) - Safe duration (min)
37 - 100 - 5
30 - 56 - 9 
25 - 37 - 14
20 - 24 - 21
15 - 16 - 31 
10 - 11 - 45

Question 4

Which arterial cannulation site provides the lowest stroke risk in HCA operations?

Answer 4

Axillary artery

Question 5

What is the maximum temperature gradient allowed between arterial inflow and venous outflow?

Answer 5

10C to prevent formation of gaseous emboli

Question 6

What are the monitoring devices used during DHCA?

Answer 6

EEG, cerebral oximetry monitoring, nasopharyngeal temperature probe, bladder probe, rectal probe, esophageal probe

Question 7

What are the general accepted parameters before initiating DHCA?

Answer 7

Cooling for 30+ minutes, nasopharyngeal temperature 18C, jugular venous saturation > 95%, EEG silence

Question 8

What are the adjuncts to DHCA?

Answer 8

Antegrade cerebral perfusion, retrograde cerebral perfusion, topical cooling (ice around head),

Question 9

How is retrograde cerebral perfusion performed?

Answer 9

It is performed by cannulating and snaring the superior vena cava and perfusing the brain with hypothermic arterial blood

Question 10

What are the accepted flow rates in RCP?

Answer 10

300-500mL/min for an SVC pressure of 20-25mmHg

Question 11

What are the three goals of RCP?

Answer 11

1. Flushing embolic material from the brain 2. Maintaining hypothermia of the brain 3. Supporting cerebral metabolism of the brain

Question 12

What are the three pharmacologic adjuncts used in DHCA?

Answer 12

Corticosteroids, mannitol and barbituates

Question 13

What are the differences between RCP vs ACP vs DHCA alone?

Answer 13

There is no consensus on the optimal strategy, however evidence shows that some form of cerebral perfusion is better than none. There is no difference between RCP and ACP with regards to permanent neurologic dysfunction but ACP reduces temporary neurologic dysfunction compared with both RCP and DHCA alone.