Chapter 26

• Regardless of the cause, intracranial masses present according to growth rate, location, and intracranial pressure. Slowly growing masses are frequently asymptomatic for long periods, whereas rapidly growing ones usually present acutely.
• Computed tomographic and magnetic resonance imaging scans should be reviewed for evidence of brain edema, a midline shift greater than 0.5 cm, and ventricular size.
• Operations in the posterior fossa can injure vital circulatory and respiratory brain stem centers as well as cranial nerves or their nuclei.
• Venous air embolism can occur when the pressure within an open vein is subatmospheric. These conditions may exist in any position (and during any procedure) whenever the wound is above the level of the heart.
• Optimal recovery of air following venous air embolism is provided by a multiorificed catheter positioned high in the atrium at its junction with the superior vena cava. Confirmation of correct catheter positioning is important and is accomplished by intravascular electrocardiography or by transesophageal echocardiography.
• In a patient with head trauma, correction of hypotension and control of any bleeding take precedence over radiographic studies and definitive neurosurgical treatment because systolic arterial blood pressures of less than 80 mm Hg correlate with a poor outcome.
• Massive blood loss from aortic or vena caval injury can occur intraoperatively or postoperatively with thoracic or lumbar procedures and is often initially occult.

Harvey Cushing, one of the founders of neurosurgery, is largely responsible for the development of the anesthesia record. Out of concern for the safety of his patients, he emphasized the need to record the surgical patient’s pulse, respiratory rate, temperature, and blood pressure intraoperatively. A better understanding of the effects of anesthesia on the central nervous system (CNS) (see Chapter 25) and improvements in anesthetic techniques have similarly contributed to the improved outcomes seen in modern neurosurgery. Sophisticated monitoring techniques and improved operating conditions under anesthesia have allowed increasingly difficult procedures to be performed on patients previously deemed inoperable.

Anesthetic techniques must be modified in the presence of intracranial hypertension and marginal cerebral perfusion. In addition, many neurosurgical procedures require unusual patient positions—eg, sitting, prone—further complicating management. This chapter applies the principles developed in Chapter 25 to the anesthetic care of neurosurgical patients.

Intracranial hypertension is defined as a sustained increase in intracranial pressure (ICP) above 15 mm Hg. Uncompensated increases in the tissue or fluid within the rigid cranial vault produce sustained ICP elevations (see Chapter 25). Intracranial hypertension may result from an expanding tissue or fluid mass, depressed skull fracture, interference with normal absorption of cerebrospinal fluid (CSF), excessive cerebral blood flow (CBF), or systemic disturbances promoting brain edema (see below). Multiple factors are often simultaneously present. For example, tumors in the posterior fossa are not only usually associated with some degree of brain edema, but they also readily obstruct CSF flow by compressing the fourth ventricle (obstructive hydrocephalus).

Although many patients with increased ICP are initially asymptomatic, all eventually develop ...

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