E Craniotomy
Intracranial masses may be congenital, neoplastic (benign, malignant, or metastatic), infectious (abscess or cyst), or vascular (hematoma or malformation). Most, but not all, anesthetics can be used safely in patients with cerebral lesions. The effects of the agent on ICP, CPP, CBF, CMRo2 (cerebral metabolic rate of oxygen), promptness of return of consciousness, drug-related protection from cerebral ischemia or edema, blood pressure control, and compatibility with neurophysiologic monitoring techniques are important considerations.
Most craniotomy surgery in the United States today is performed after a propofol induction of anesthesia with intubation of the trachea after a nondepolarizing relaxant. Maintenance of anesthesia is commonly accomplished with a combination of an inhalation agent (usually isoflurane) and narcotic such as fentanyl, sufentanil, or alfentanil in various combinations during maintenance of low normocarbia.
2. Preoperative assessment
a) The clinical signs of a supratentorial mass include seizures, hemiplegia, and aphasia. The clinical signs of infratentorial masses include cerebellar dysfunction (ataxia, nystagmus, dysarthria) and brainstem compression (cranial nerve palsies, altered consciousness, abnormal respiration). When ICP increases, frank signs of intracranial hypertension can also develop.
b) Preanesthetic evaluation should attempt to establish the presence or absence of intracranial hypertension. CT or magnetic resonance imaging (MRI) data should be reviewed for evidence of brain edema, midline shift greater than 0.5 cm, and ventricular size. A neurologic assessment should evaluate the current mental status and any existing neurologic deficits.
c) Medications prescribed for the control of ICP (corticosteroids, diuretics) and anticonvulsant therapy should be reviewed. Laboratory evaluation should rule out corticosteroid-induced hyperglycemia and electrolyte disturbances (such as SIADH or DI) that may develop secondary to diuretic therapy. Anticonvulsants, dosage time of last dose, and blood levels should be noted.
d) The decision regarding the amount and timing of the premedication administration should be made only after a thorough patient evaluation. Benzodiazepines produce respiratory depression and hypercapnia. Premedication should be omitted in patients with a large mass lesion, a midline shift, and abnormal ventricular size. Opioids are universally avoided in the preoperative period. If premedication is desired in patients deemed appropriate, careful titration of IV midazolam may begin when the patient has been delivered to the preoperative holding area. In an attempt to help control ICP in patients with mass lesions, the head of the bed should be elevated 15 to 30 degrees during transport to the preoperative holding area and the operating room.
3. Perioperative management
a) Intraoperative monitoring
(1) Routine monitors for supratentorial procedures include continuous ECG, cuff measurement of blood pressure, precordial stethoscope, monitoring of the fraction of inspired oxygen, pulse oximetry, temperature, peripheral nerve stimulation, etco2 monitoring, and indwelling urinary catheterization.
(2) For patients with ischemic heart disease, use of a modified V5 ECG lead is recommended. An arterial line placed either before or immediately after anesthetic induction provides for uninterrupted blood pressure monitoring and easy access for blood sampling for laboratory analysis.
b) Fluid management
(1) Preoperative fluid deficits and intraoperative blood and fluid losses must be adequately replaced during neurosurgical procedures. Judicious fluid administration minimizes the occurrence of cerebral edema and increased ICP, reduced CPP, and worsened cerebral ischemia.
(2) In most neurosurgical patients, fluids that contain osmolarity similar to that of serum (e.g., lactated Ringer solution or 0.9% saline) are administered in a volume that is sufficient for the maintenance of peripheral perfusion but that avoids hypervolemia (0.5 to 1 mL/kg/hr).
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