• Cessation of the systemic circulation is either
  • Unintentional: Due to cardiac arrhythmia or arrest, ischemia, electrolyte abnormality, or extreme hypothermia.
  • Therapeutic (planned or emergent): Hypothermic circulatory arrest temporarily suspends blood flow under very cold body temperatures to allow for a motionless and bloodless surgical field for intracardiac and aortic procedures. This requires increased coordination among the anesthesiologist, surgeon, and perfusionist.
• At cold temperatures, cellular activity levels slow significantly and allow blood circulation to be suspended for up to 40 minutes without neurological harm to the patient.
• Additionally, adjunctive selective cerebral perfusion (antegrade or retrograde) is commonly used now, whereas previous deep hypothermic circulatory arrest (DHCA) relied on hypothermia alone for neuroprotection.

• Unintentional: High/normal cerebral metabolic rate of oxygenation (CMRO₂) during periods of limited or no cerebral perfusion may rapidly lead to irreversible hypoxic brain injury.
• Therapeutic: CMRO₂ decreases 7%/°C. At 23°C, the CMRO₂ theoretically approaches zero. Types of cerebral perfusion include retrograde and antegrade.
• Retrograde cerebral perfusion (RCP)
  • Cannulation is via the superior vena cava (SVC).
  • Perfusion with cold blood
  • Perfusion theoretically occurs via the SVC to the internal jugular (IJ) vein to the sigmoid sinuses to the venules to the capillaries to the arterioles to the circle of Willis (coW) to the internal carotid artery (ICA) to the right and left common carotid arteries (RCC/LCC) and then to the aortic arch.
  • Conventional maximum flow rate of 500 mL/min in the circuit is utilized to maintain the SVC catheter pressure <25 mm Hg.
  • Advantages
    • More homogenous brain cooling
    • Washout of air bubbles, embolic debris, and metabolic waste products
    • Prevention of cerebral blood cell microaggregates
    • Delivery of O₂ and metabolic substrates
  • Potential disadvantages
    • Excessive RCP pressure has been related to the potential for increased cerebral edema leading to neurologic injury (1).
    • Increased intracranial pressure and cerebral edema may occur due to direct perfusion of hypothermically vasoconstricted microvasculature and tissues. Impeded venous return may also exacerbate intracranial pressure and edema.
    • Low levels of substrate
    • Duration before cerebral consequences: 45 minutes
• Anterograde cerebral perfusion
  • The right axillary artery is either directly cannulated or a graft is inserted.
  • Perfusion with cold blood
  • Once antegrade perfusion is initiated, the brachiocephalic artery is clamped, and blood flow proceeds from the right axillary artery to the right subclavian artery to the brachiocephalic artery (very short segment) to the RCC and then to the brain.
  • Mean perfusion pressure usually 40–70 mm Hg.
  • Cerebral oximetry may be used to evaluate changes in regional brain perfusion. If left-sided cerebral perfusion decreases, direct visual cannulation of the left carotid artery and perfusion with cold blood may be performed to enhance flow.
  • Advantages
    • Uninterrupted supply of nutrients to the brain
    • Prolonged duration of safe circulatory arrest compared to RCP
  • Potential disadvantages
    • Air or plaque emboli due to manipulation of frequently atheromatous great vessels and direct antegrade flow to the cerebral circulation.
    • Unilateral flow requires an intact coW, which is present in only ~30% of the population. The most common absences include a lack of the P1 segment of the posterior cerebral artery (PCA), posterior communicating artery (PComm), or A1 segment of the anterior cerebral artery (ACA). Prior ischemic stroke in any of these territories may also result in an incomplete circle (2).
    • Axillary cannula or graft insertion can increase the complexity of surgery.
    • A greater number of cannulae are present on the surgical field.
    • Duration before cerebral consequences: 60 minutes.
• Controversial topics
  • Optimal lowest temperature is unknown. While hypothermia decreases the CMRO₂ (provides neuroprotection), it can adversely affect coagulation and microvascular perfusion; profound hypothermia (~14°C) may have more profound adverse effects. In addition, lower temperature is associated with longer cardiopulmonary bypass (CPB) times due to longer rewarming times (longer CPB time is associated with poorer outcomes). With the advent of antegrade cerebral perfusion, the duration of circulatory arrest may be prolonged, and decreased levels of hypothermia may be utilized (up to 25°C) (3).
  • Optimal flow rate and pressure are unknown. Both flow and perfusion pressure should meet tissue metabolic requirements without causing tissue injury. Although conventional values have been established, whether they should be adjusted for temperature-related differences in vascular tone is not known.
  • Barbiturates or propofol may be used for neuroprotection in conjunction with EEG monitoring. Isoelectric EEG implies decreased CMRO₂ and improved cerebral protection. However, studies have shown that patients receiving thiopental required more inotropic support, but significant neuroprotection was not provided (4).
  • Steroids (large-dose methylprednisolone 30 mg/kg) are also commonly used for neuroprotection, but experimental results are mixed. for example, one animal study found that systemic pretreatment fails to attenuate neuronal cell injury after prolonged DHCA and that the steroid group showed increased neuronal apoptosis in the dentate gyrus (5). However, another study found improved global and regional cerebral blood flow (CBF) and CMRO₂ with steroid use (6).

Therapeutic circulatory arrest is used for large or difficult to access cerebral aneurysms and aortic repair in order to create a motionless, bloodless field. Continuous circulation during open exposure of the aortic arch or cerebral circulation would create a difficult surgical field or massive hemorrhage.

Brachiocephalic artery repair. Loss of the left radial arterial line waveform can occur during left-sided repair.

• Inadequate cardioprotection
  • Cardiac ischemia may occur due to inadequate cardioplegia administration or inability to terminate electrical activity during circulatory arrest.
  • Inability to wean from CPB may be secondary to myocardial stunning.
  • Ventricular fibrillation may occur during rewarming. Arrhythmias may also occur postoperatively.
• Hypothermia
  • Hemoconcentration with hypothermia and increased blood viscosity may decrease microvascular perfusion.
  • Consider isovolemic hemodilution
• Coagulopathy
  • Temperatures required for protection are outside the normal range of coagulation enzymes.
  • Increased bleeding after termination of CPB and protamine administration
  • Consider antifibrinolytics, DDAVP, autologous blood transfusion, early plasma, and factor administration based on clinical evaluation or coagulation panels.
• Postoperative shivering
  • Increased metabolic rate
  • Increased O₂ consumption
• Cerebral injury is a major cause of morbidity and mortality following aortic arch surgery.
  • Stroke due to insufficient neuroprotection may occur early (temporary neurological dysfunction) or late (permanent neurological dysfunction) due to cerebral hypoperfusion or atheromatous emboli. It may be due to ischemia reperfusion injury or rewarming injury.
  • Spinal cord ischemia due to prolonged arrest of vertebral artery flow. Neuromonitoring techniques may be used to detect changes.
• Inadequate lower body organ protection
  • Renal insufficiency
  • Hepatic ischemia
• Decreased metabolic rate
  • Metabolism of most drugs is decreased while hypothermic.
  • Muscle relaxation may outlast sedation postoperatively, especially if redosed.
• General end-organ effects
  • Endothelial dysfunction
  • Apoptosis
  • Necrosis
• Stress response and hyperglycemia
  • May be refractory to insulin during circulatory arrest and then increasingly sensitive with rewarming.
  • Aggressive, tight treatment is usually not warranted.

• Cardiopulmonary Bypass
• Neuroprotection
• Thoracic Aneurysm Repair Repair
• Craniotomy, Cerebral Aneurysm Clipping
• Hypothermia

427.5 Cardiac arrest

I46.9 Cardiac arrest, cause unspecified

January Y. Tsai , MD