List the complications and their likely underlying mechanisms specifically related to cardiopulmonary bypass that may be seen in the ICU following cardiac surgery.
a)
Effects related to blood contact with non-biologic surfaces and blood-gas interfaces
b)
Effects related to non-pulsatile flow
c)
Effects related to haemodilution
d)
Effects of hypothermia
e)
Effects of heparin and protamine
f)
Effects related to aortic manipulation (cross-clamping and proximal grafts)
g)
Other
Additional comments:
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.
There are several different ways to answer ths, as has been pointed out by the examiners. The previous (identical) incarnation of this SAQ was Question 1 from the second paper of 2011; in their model answer the college had classified the complications by organ system. Both approaches are available for revision, presented as tables in the chapter on complications attributed to the cardiopulmonary bypass circuit. Below, the revising candidate can see a tabulated form of the alternative college answer from 2011.
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 |
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.