5.1 CABG Complications

Question 1

Q1 — CABG complications
a) What are the central and peripheral neurological complications of coronary artery bypass surgery?

Answer 1

● Stroke.
● Cognitive dysfunction.
● Visual field defects.
● Subtle sensory-motor deficits

Question 2

b) List any five risk factors for central neurological complications in these surgeries.

4 marks

Answer 2

Patient factors:
● Age >70 years.
● Significant cerebrovascular disease.
● Extensive aortic atherosclerosis.
● Diabetes mellitus

Surgical factors:
● Open chamber surgical procedures.
● Duration of cardiopulmonary bypass >90 minutes.
● Perioperative haemodynamic instability.
● Multiple aortic manipulations (repeated clampings, cannulations).

CPB — equipment factors:
● Use of bubble oxygenators
(rather than membrane oxygenators).
● Lack of arterial inflow line filters.
● Use of nitrous oxide

Question 3

c) What are the pathophysiologic mechanisms involved in the neurologic complications after these surgeries?

Answer 3

1. Hypotension
   Risk in both on and off pump bypass
   - significant drops in MAP cause a reduction in CPP (CPP = MAP-CVP)
   Reduction in perfusion to brain parenchyma can cause areas of ischaemi
2. CVA
   Ischaemic and Thrombotic or embolic phenomena
   Aortic plaques distruption from handling
   and microemboli can cause CVA
3. Air emboli
   Emboli of air going to the brain can cause stroke like complicaiton
4. Hypoxia / reduced Do2

● Hypoperfusion — poor cerebral autoregulation.

● Focal ischaemia:
- emboli (air, atheroma, clots);
- during open heart procedures;
- from the aorta during cannulation/clamping;
- intraventricular thrombi.

● Global ischaemia —
severe hypoperfusion,
circulatory arrest.

● Inadequate cerebral protection.

● Reperfusion injury.

● pH stat management —
vasodilation could increase embolic load.

Question 4

d) Name any four intraoperative techniques that are used for monitoring cerebral perfusion during cardiac surgery.

Answer 4

● EEG — processed EEG such as BIS.

● Evoked potentials.

● Transcranial Doppler.

● Jugular oxymetry.

● Non-invasive optical spectroscopy.

Question 5

e) List four techniques that could reduce the incidence of central neurological complications.

Answer 5

● Avoidance of inadvertent hypotension.

● Reduce emboli during aortic cannulation —
US scanning of aortic segment.

● Slow rewarming.

● Use of microfilters in the CPB circuitry.

● Meticulous de-airing techniques.

● Cerebral protection —
pharmacological and non-pharmacological
(cooling).

● Maintenance of euglycaemia.