Question 29

Highest mark
6.5
Pass rate
22%
Other SAQs in this topic:
Other SAQs in this paper:

In relation to cardiac surgery:

a)    What are the complications of aortic cross clamping and cardiopulmonary bypass that may affect the post-operative ICU management?    (80% marks)

b)    What are the major risks from internal mammary artery grafting? (10% marks)

c)    What are the major risks from radial artery grafting? (10% marks)
 

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College answer

a)

Respiratory complications:

  • Left lower lobe collapse (poor re-inflation post bypass, phrenic nerve injury)
  • Increased pulmonary vascular resistance (protamine)
  • Acute lung injury (SIRS)
  • Pulmonary oedema
  • ?pneumothorax

Cardiovascular complications

  • Myocardial stunning or infarction (inadequate myocardial protection)
  • Coronary graft ischaemia (air embolism)
  • Right ventricular dysfunction (pulmonary hypertension related to protamine)
  • Hypoperfusion and end-organ ischaemia related to non-pulsatile flow and/or air/atheroma embolism from cross clamping
 
  • Aortic dissection from cross clamping

Neurological complications

    • Cerebrovascular events, watershed infarcts,
    • neurocognitive dysfunction (low flow, thromboembolism)
    • Phrenic nerve palsy (use of cold cardioplegia ‘slush’)

Renal complications

  • Dysfunction related to ischaemia (non-pulsatile flow) and SIRS

Gastro-intestinal complications

  • Splanchnic ischaemia (low flow, thromboembolism)
  • Hepatitic dysfunction, acalculous / gangrenous cholecystitis, pancreatitis (hypoperfusion, SIRS)

Haematological complications

  • Coagulopathy (effects of hypothermia and dilutional coagulopathy, residual heparinisation, activation of coagulation cascade during bypass)
  • Anaemia (haemodilution, blood loss in the circuit)
  • Platelet dysfunction (bypass circuit) Haemolysis (bypass circuit)
  • Bleeding from aortic cannulation site Metabolic complications
  • Hypothermia (intra-operative cooling and delayed re-warming)
  • Insulin resistance and hyperglycaemia (hypothermia)
  • Electrolyte abnormalities (haemodilution, post-pump diuresis)

Immune-mediated complications

  • Activation of coagulation cascade (blood contact with non-biological surfaces and blood-gas interface)
  • SIRS (leucocyte and complement activation, cytokine release and expression of adhesion molecules stimulated by contact with bypass circuit)
  • Allergic reactions to protamine

ALTERNATIVE TEMPLATE BASED ON PATHOPHYSIOLOGY

  1. 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
  1. Effects related to non-pulsatile flow
    • Renal dysfunction
    • Cerebrovascular events, watershed infarcts, neurocognitive dysfunction
    • Splanchnic ischaemia
  1. Effects related to haemodilution
    • Dilutional coagulopathy, anaemia.
    • Electrolyte abnormalities
 
  1. Effects of hypothermia
    • Coagulopathy
    • Decreased tissue oxygen delivery
    • Insulin resistance and hyperglycaemia
  1. Effects of heparin and protamine
    • Residual heparinisation leading to bleeding
    • Increased pulmonary vascular resistance and right ventricular dysfunction from protamine, allergic 
reactions to protamine
  1. f) Effects related to aortic manipulation (cross-clamping and proximal grafts)
    • Systemic embolisation with potential for neurologic, mesenteric and renal dysfunction.
    • Aortic dissection from cannulation site
    • Bleeding from bypass cannulation site
    • Difficulty      with      myocardial      protection      resulting      in      postoperative myocardial dysfunction (especially right-sided) due to stunning or infarction
  1. g) Other
    • Left phrenic nerve palsy (surgical injury, use of cold cardioplegia “slush”)
    • Left lower lobe collapse (poor re-inflation post bypass, phrenic nerve injury)

b)

Artery spasm/kinking/thrombosis - resultant myocardial ischaemia/LVF

Increased risk of sternal devascularisation-> sternal non-union and infection especially with bilateral IMA grafts

Increased post-op bleeding with bilateral IMA harvesting Aneurysm/pseudo-aneurysm of artery formation

c)

Spasm -> cardiac ischaemia

Arm complications-> haematoma/haemorrhage, infection, motor impairment (usually temporary), sensory impairment, pain, distal ischaemia (rare)

Examiners Comments:

Answers generally lacked structure and detail.

Discussion

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
Pancreatitis
Splanchnic ischaemia
Mechanics of surgery Atelectasis (especially of the  LLL) due to mechanical compression
Embolic complications Myocardial infarction
Stroke (eg. air or cholesterol emboli)
Splanchnic ischaemia
Limb ischaemia

Complications of internal mammary artery grafting (von Segesser et al, 1990)

  • Spasm of the graft may occur (whereas with SVG, it will not)
  • Potendial devascularisation of the chest wall may increase the risk of sternal wound dehiscence
  • Wound complications are thought to be more common with bilateral IMA grafting
  • Pneumothorax is more likely
  • Prenic nerve paresis is more likely
  • Chylothorax may occur duet to thoracic duct injury
  • Subclavian steal may develop

Complications of radial artery grafting (Budillon et al, 2003; Buxton et al, 1996)

  • Donor arm weakness in ~ 0.7%
  • Cutaneous paraesthesia in ~ 3.7%
  • Potential for hand ischaemia
  • Spasm of the graft may occur (whereas with SVG, it will not)

References

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.

Eagle, Kim A., et al. "ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1999 Guidelines for Coronary Artery Bypass Graft Surgery)." Circulation 110.14 (2004): e340.

von Segesser, Ludwig K. "Complications of Internal Mammary Artery Grafting." Arterial Grafting for Myocardial Revascularization. Springer, Berlin, Heidelberg, 1990. 102-108.

Budillon, Alessandro Maria, et al. "Complications after radial artery harvesting for coronary artery bypass grafting: our experience." Surgery 133.3 (2003): 283-287.

Buxton, Brian, et al. "The radial artery as a bypass graft." Current opinion in cardiology 11.6 (1996): 591-598.

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