Question 16

College answer

Not available.

Discussion

a) Rationale:

• Surgical access
  • The surgical approach to the replacement or repair of the aortic arch and aortic root requires that at some stage the aorta be incised and open to air.
  • It is impractical to do this with normal circulation: air emboli and blood loss would be prohibitive
  • Circulation must therefore cease while the aortic root is opened
• Organ protection
  • Hypothermia protects the organs during circulatory arrest
  • This is the result of a decreased metabolic rate
  • At 18º C, cerebral metabolic rate decreases to something like 10-15% of the normal rate seen at 37º C
  • At this temperature, complete circulatory arrest can be well tolerated for up to 30 minutes

b) Indications:

• Cardiac surgery:
  • Aortic arch reconstruction (aneurysm, rupture, dissection)
  • Pulmonary thromboendarterectomy
  • Repair of complex congenital heart defects (transposition of the great arteries, total anomalous pulmonary venous return, hypoplastic left heart syndrome)
  • Vascular reconstruction during cardiac transplant
• Non-cardiac surgery:
  • Surgery on the thoracoabdominal aorta
  • Repair of giant cerebral aneurysms
  • Resection of cerebral arteriovenous malformations
  • Resection of renal cell carcinoma with caval invasion
  • Resection of other tumors with caval invasion

c) Adverse effects:

• Respiratory complications:
  • Hypoxia due to atelectasis
  • ARDS (if prolonged bypass)
• Circulatory complications:
  • Low cardiac output states (if prolonged bypass time)
  • Arrhythmias (especially if incompletely rewarmed)
• Neurological complications:
  • Stroke (mainly embolic, and mainly in those who had more than 40 minutes of DHCA)
  • Seizures
  • Choreoathetosis (usually develops 2-6 days following the surgery; seems to be related to temperatures below 15º C)
  • Decreased cognitive function
  • Spinal cord ischaemia 
• Renal complications
  • Acute kidney injury
• Hepatic complications:
  • LFT derangement
• Haematological complications:
  • Coagulopathy