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.
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.