Chapter 18

Patients with impaired cerebral blood flow (CBF) may require either surgical or endovascular revascularization. A comprehensive team approach is required to optimize the cerebral perfusion pressure (CPP) and local metabolic needs of the brain in this setting. Familiarity with the use of multiple technologies and pharmacologic agents are important in achieving a good outcome, and maintenance of adequate CPP during this period is critically important to avoid ischemic injury. CPP is determined by multiple factors, the most important of which is the mean arterial pressure (MAP) as detailed below (Table 18.1). In these delicate patients, dangerous hemodynamic instability may occur at any time, including prior to and during induction, during the procedure, and in the postoperative period (Table 18.2).

Preoperative Preparation

Blood Pressure and Cerebral Perfusion Pressure

As mentioned, maintenance of adequate CPP is the most important factor in avoiding ischemic injury in this population. At our center, an arterial line is placed for all procedures in this patient population. Medications to optimize the systolic blood pressure (BP) and MAP are used on a routine basis to protect the CPP. In our practice, we commonly use a combination of clevidipine or nicardipine with Neo-Synephrine (Bayer Consumer Health, Morristown, NJ) to achieve an optimal MAP. If necessary, dopamine may be used for bradycardia while dobutamine is used for lower cardiac index. We monitor the cardiac index with an arterial line using a flotrac device from Edwards Life Sciences (Irvine, CA).

Airway and Oxygenation

Direct access to the airway may be limited during surgical or neurointerventional revascularization. A proper secure airway must therefore be ensured prior to the start of the procedure.

Electrolytes

Sodium, potassium, calcium, phosphorus, and magnesium are checked and corrected prior to the revascularization procedure. Sodium is kept at a high normal level to limit perioperative ictal activity and to reduce the risk of cerebral edema. The fluid of choice is generally normal saline (sodium concentration of 154 mmol/L) as compared with ringer’s lactate (which has only 132 mmol/L). In addition to sodium, magnesium has been shown to play an important role in neuronal excitability.¹ Magnesium is checked and replaced, and kept at a high normal value, preferably using a standardized replacement protocol.

Cardiac

As possible given time constraints, cardiac screening is done to limit the potential perioperative risk for cardiac morbidity. Care should be used when administering a preoperative β-blocker before neurovascular procedures due to its rate-limiting effect, which can ultimately reduce the cardiac index. This may lead to a reduction in the CBF and CPP (Table 18.3). For carotid endarterectomy and extracranial-intracranial (EC-IC) bypass procedures, an aspirin is given to reduce the risk of postoperative stroke. Use of a β-blocker may be warranted in these procedures if there is a history of coronary artery disease.

Abbreviations: MAP, mean arterial pressure; CPP, cerebral perfusion pressure; ICP, intracranial pressure.

Special Situations

Pregnancy is a challenge during revascularization. If an endovascular procedure is contemplated, the patient is prepared by adequate shielding. The risk–benefit ratio of possible prolonged exposure is discussed with the patient.

Patients with a history of possible significant intravenous (IV) dye reactions are prepared using a steroid protocol. The tubing for the IV and the pressure monitoring is kept at a greater length than usual. The oxygen sensor is placed on the lower limb on the side of the femoral access to check for early blood flow compromise. It is preferable to use one port for medication infusion for better access, and staff can label this port with color-coded tape prior to the procedure.

Intraoperative Anesthetic Considerations

Anesthetics Effect

Different agents are used to induce and maintain the anesthesia depth in patients who will undergo a cerebral revascularization procedure. The limitation of blood flow and potential for postprocedural hyperperfusion of the brain should always be considered. Thiopental loading may reduce postcardiopulmonary bypass neurologic deficits. This agent can be used effectively during the acute resuscitation of malignant intracranial pressure, reducing the metabolic activity of the brain. Most routinely used volatile anesthetics will similarly reduce the metabolic activity of the brain, and propofol can reduce the cerebral metabolic rate of oxygen (CMRO₂) by 50%, which helps combat the reduced blood flow during these procedures.² Etomidate will suppress the electroencephalographic (EEG) results but will not cause the myocardial depression that may be seen with other previously mentioned agents. In theory, etomidate, thiopental, and ketamine can all reduce nitric oxide levels in acute ischemic stroke (AIS), which could reduce blood flow to the penumbra area.³ In addition, etomidate is a potent suppressant of corticosteroid synthesis in the adrenal gland, which may become important in a hypotensive bypass patient.⁴

Abbreviations: α, directly proportional; CI, cardiac index; CPP, cerebral perfusion pressure; MAP, mean arterial pressure; ICP, intracranial pressure; BSA, body surface area; SVR, systemic volume resistance.

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