List the complications and their likely underlying mechanisms specifically related to cardiopulmonary bypass that may be seen in the ICU following cardiac surgery.
Answer and interpretation
a) Effects related to blood contact with non-biologic surfaces and blood-gas interfaces
- Activation of coagulation cascade- consumptive coagulopathy, thromboembolic phenomena, haemolysis, rarely TTP.
- Systemic inflammatory response syndrome due to leucocyte and complement activation, cytokine release and expression of adhesion molecules- vasodilatory shock, fever, acute lung injury, liver dysfunction, multiorgan dysfunction.
- Platelet dysfunction
b) Effects related to non-pulsatile flow
- Renal dysfunction
- Cerebrovascular events, watershed infarcts, neurocognitive dysfunction
- Splanchnic ischaemia
c) Effects related to haemodilution
- Dilutional coagulopathy, anaemia.
- Electrolyte abnormalities
d) Effects of hypothermia
- Decreased tissue oxygen delivery
- Insulin resistance and hyperglycaemia
e) Effects of heparin and protamine
- Residual heparinisation leading to bleeding
- Increased pulmonary vascular resistance and right ventricular dysfunction from protamine, allergic reactions to protamine
f) Effects related to aortic manipulation (cross-clamping and proximal grafts)
- Systemic embolisation with potential for neurologic, mesenteric and renal dysfunction.
- Difficulty with myocardial protection resulting in postoperative myocardial dysfunction (especially right-sided) due to stunning or infarction
- Left phrenic nerve palsy (surgical injury, use of cold cardioplegia “slush”)
- Left lower lobe collapse (poor re-inflation post bypass, phrenic nerve injury)
- Pass rate: 63%
- Highest mark: 8.8
- Candidates who failed did not address complications specific to CP bypass and/or did not describe the underlying mechanisms. Some answers were poorly structured with a tendency to repeat points.
- The above answer template is not the only way to structure the answer, for example the complications could be classified by body system affected.