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.
| 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 Endocrine |
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 | ||
| Pancreatitis | ||
| 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 |
| 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 | |
| Pancreatitis | |
| Splanchnic ischaemia | |
| Mechanics of surgery | Atelectasis (especially of the LLL) due to mechanical compressio |
| Embolic complications | Myocardial infarction |
| Stroke | |
| Splanchnic ischaemia | |
| Limb ischaemia |
References
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.