Complications attributed to the cardiopulmonary bypass circuit

This relates to Question 1 from the second paper of 2011, and the identical Question 2 from the first paper of 2015: "List the complications and their likely underlying mechanisms specifically related to cardiopulmonary bypass that may be seen in the Intensive Care Unit following cardiac surgery."  A slightly altered version of this SAQ appeared as Question 29 from the first paper of 2020. It was  reworded into asking for "the complications of aortic cross clamping and cardiopulmonary bypass that may affect the post-operative ICU management". On close inspection, the content is identical.
The answer offered by the college lists the complications according to the systems they have affected, in an A, B, C, D, E pattern. The alternative answer in Question 1  is organised by physiological process responsible for the complication. Both styles are presented as tables below. In addition to this brief summary, long form notes on the complications of coronary artery bypass surgery  are also available.

Complications of Cardiopulmonary Bypass
Organised According to Organ Systems
Organ System Complication Aetiology
Respiratory Left lower lobe collapse Phrenic nerve neuropraxia, due to cold slush cardioplegia
Poor reinflation following restoration of circulation
Pulmonary hypertension Due to increased pulmonary vascular resistance (protamine)
Acute Lung Injury SIRS due to bypass circuit-associated complement activation
Cardiovascular Myocardial stunning Due to direct effects of cardiotomy and cardioplegia
Myocardial infarction Coronary graft ischaemia (air embolism)
RV dysfunction Due to pulmonary hypertension related to protamine
Arrhythmias Due to electrolyte disturbances and hypothermia
Heart block Due to hypothermia or direct conduction system trauma
Systemic MODS Hypoperfusion and end-organ ischaemia related to non-pulsatile flow and/or air/atheroma embolism
Neurological Stroke All thought to be due to the sluggish low-flow state following the recommencement of bypass, as well as due to air emboli microemboli and possibly microemboli from the bypass circuit itself
Watershed infarcts
Neurocognitive impairment
Electrolytes and
Hypothermia Due to intra-operative cooling and delayed re-warming
Hyperglycaemia Due to hypothermia-related insulin resistance
Due to circulating endogenous catecholamines
Electrolyte derangement Haemodilution
Renal Post-op diuresis "Cold diuresis" due to intra-operative cooling and delayed re-warming
Post-op renal failure Low flow, and thromboembolic events
Electrolyte derangement Haemodilution
Gastrointestinal Splanchnic ischaemia Low flow, and thromboembolic events
Hepatic dysfunction
Haematological Coagulopathy Due to consumption of clotting factors by the bypass circuit
Due to residual anticoagulation
Due to dilutional coagulopathy
Platelet dysfunction Due to antiplatelet agents, and due to the SIRS response
Anaemia Due to haemodilution and haemolysis
Haemolysis Due to mechanical destruction by the bypass pump, as well as due to MAHA and SIRS
Metabolic Hypothermia Due to intra-operative cooling and delayed re-warming
Hyperglycaemia Due to hypothermia-related insulin resistance
Due to circulating endogenous catecholamines
Immune Coagulation cascade activation Due to blood contact with non-biological surfaces and blood-gas interface
SIRS Due to complement activation by circuit components
Anaphylaxis A reaction to protamine
Complications of Cardiopulmonary Bypass
Organised According to Physiological Derangement
Aetiology Physiological derangement
Bypass circuit mechanism Hemodilution
Haemolysis (mechanical)
Blood loss into the circuit
SIRS due to bypass
SIRS due to bypass Coagulopathy due to coagulation cascade activation and clotting factor depletion
Platelet dysfunction and platelet depletion
Renal failure due to SIRS
Acute lung injury due to SIRS, "pump lung"
Anticoagulation and reversal Bleeding from residual heparin
Heparin-induced thrombocytopenia
Anaphylaxis to protamine
Increased pulmonary resistance due to protamine
Right ventricular failure due to protamine-induced pulmonary hypertension
Prolonged hypothermia Heart block
Ventricular and atrial arrhythmias
Hyperglycaemia (decreased insulin production as well as insulin insensitivity)
Decreased tubular resorption in the kidney (thus diuresis)
Phrenic nerve palsy (“cold slush cardioplegia”)
Prolonged ischaemia Renal failure due to ATN
Myocardial infarction
Encephalopathy and neurocognitive deterioration
Hepatic dysfunction and delayed drug clearance
Splanchnic ischaemia
Mechanics of surgery Atelectasis (especially of the  LLL) due to mechanical compressio
Embolic complications Myocardial infarction
Splanchnic ischaemia
Limb ischaemia


Frederick A. Hensley, Jr., M.D., Donald E. Martin, M.D.,  Glenn P. Gravlee, M.D. A Practical Approach to Cardiac Anaesthesia, 3rd ed. Sibylle A. Ruesch and Jerrold H. Levy. CHAPTER 9. The Postcardiopulmonary Bypass Period: A Systems Approach. 2003 by LIPPINCOTT WILLIAMS & WILKINS

André, Arthur C. St, and Anthony DelRossi. "Hemodynamic management of patients in the first 24 hours after cardiac surgery." Critical care medicine 33.9 (2005): 2082-2093.

Ray Raper's chapter in Oh's manual (pp.285)

Complications in cardiothoracic surgery: avoidance and treatment, Little A.G, Merril W.H. � 2007, 2nd ed. Chapter 4 by Creswell and Karis.

Cardiopulmonary bypass- Principles and Practice, Gravlee G.P. and Davis R.F -2007 (3rd ed.)

UpToDate contains a couple of excellent summary pieces on cardiac and non-cardiac complications of CABG.