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INTRODUCTION

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Deep hypothermic circulatory arrest (DHCA) is an established technique used during certain types of surgery in which blood flow ceases in all blood vessels while the patient’s core body temperature is lowered dramatically. Its use was first reported in 1959 in children undergoing repair of Tetralogy of Fallot. DHCA is necessary for cardiac surgery in which standard cannulation of the proximal aorta will not achieve cerebral perfusion. Circulatory arrest enables the surgeon to operate in a bloodless field with improved exposure since no cannulae or clamps are necessary. At the same time, deep hypothermia decreases cerebral metabolism and oxygen consumption, enabling a longer period to operate during interrupted cerebral perfusion. Since the brain is the organ most susceptible to ischemia, adequate cerebral protection implies that other vital organ systems should be protected as well.

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INDICATIONS

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  1. 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

  2. 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

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DHCA TECHNIQUE AND ANESTHETIC CONCERNS

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The basic components of achieving deep hypothermic circulatory arrest are as follows:

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  • Ensure adequate anticoagulation prior to commencement of DHCA

  • Eliminate glucose from all intravenous solutions to reduce the risk of hyperglycemia

  • Administer anesthetics and neuromuscular blocking drugs to decrease oxygen consumption and ensure paralysis

  • Deep levels of anesthesia may decrease the harmful physiologic stress responses to DHCA

  • Reduce temperature to 15–22°C. The cooling should occur slowly (over 30–60 minutes) to ensure homogenous hypothermia.

  • Maintain full flow CPB for at least 30 minutes to ensure adequate cerebral cooling

  • Verify cerebral electrical silence on electroencephalography or bispectral index

  • Establish circulatory arrest by discontinuing CPB flow. At normothermia, brain injury occurs after around four minutes of circulatory arrest. But the duration of DHCA that is considered safe is controversial. After 40 minutes of circulatory arrest, the stroke rate increases. After 65 minutes, overall mortality increases.

  • When feasible, maintaining a low level of pulsatile CPB flow (“trickle”) improves microcirculatory flow and the balance between myocardial oxygen supply and demand.

  • The optimal hematocrit during DHCA is unknown. Hemodilution improves the microcirculation but may lead to cerebral hypoxia.

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Rewarming the patient from DHCA is not without risk. Initial reperfusion with cold blood for at least 10 minutes prior to rewarming enables removal of metabolic waste and free radicals. By increasing cerebral blood flow, excessively rapid rewarming increases the risk of cerebral edema, embolization, and hyperthermic cerebral injury. Rewarming should be gradual and cease at 37°C (nasopharyngeal), 36°C (esophageal), or 34°C (bladder). The gradient between core and peripheral temperature should be 5–8°C. Extracranial sites of temperature monitoring underestimate brain temperature by ...

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