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  • Image not available.Cerebral perfusion pressure is the difference between mean arterial pressure and intracranial pressure (ICP) (or central venous pressure, whichever is greater).
  • Image not available.The cerebral autoregulation curve is shifted to the right in patients with chronic arterial hypertension.
  • Image not available.The most important extrinsic influences on cerebral blood flow (CBF) are respiratory gas tensions—particularly Paco2. CBF is directly proportionate to Paco2 between tensions of 20 and 80 mg Hg. Blood flow changes approximately 1–2 mL/100 g/min per mm Hg change in Paco2.
  • Image not available.CBF changes 5–7% per 1°C change in temperature. Hypothermia decreases both cerebral metabolic rate and CBF, whereas pyrexia has the reverse effect.
  • Image not available.The movement of a given substance across the blood–brain barrier is governed simultaneously by its size, charge, lipid solubility, and degree of protein binding in blood.
  • Image not available.The blood–brain barrier may be disrupted by severe hypertension, tumors, trauma, strokes, infection, marked hypercapnia, hypoxia, and sustained seizure activity.
  • Image not available.The cranial vault is a rigid structure with a fixed total volume, consisting of brain (80%), blood (12%), and cerebrospinal fluid (8%). Any increase in one component must be offset by an equivalent decrease in another to prevent a rise in intracranial pressure.
  • Image not available.With the exception of ketamine, all intravenous agents either have little effect on or reduce cerebral metabolic rate and CBF.
  • Image not available.With normal autoregulation and an intact blood–brain barrier, vasopressors increase CBF only when mean arterial blood pressure is below 50–60 mm Hg or above 150–160 mm Hg.
  • Image not available.The brain is very vulnerable to ischemic injury because of its relatively high oxygen consumption and near-total dependence on aerobic glucose metabolism.
  • Image not available.Hypothermia is the most effective method for protecting the brain during focal and global ischemia.
  • Image not available.Both animal and human data suggest that barbiturates are effective for brain protection in the setting of focal ischemia.

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The anesthetic care of patients who undergo neurosurgery requires a basic understanding of the physiology of the central nervous system (CNS). The effects of anesthetic agents on cerebral metabolism, blood flow, cerebrospinal fluid (CSF) dynamics, and intracranial volume and pressure are often profound. In some instances, these alterations are deleterious, whereas in others they may actually be beneficial. This chapter reviews important physiological concepts in anesthetic practice and then discusses the effects of commonly used anesthetics on cerebral physiology. Although most of the discussion focuses on the brain, the same concepts also apply, at least qualitatively, to the spinal cord.

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Cerebral Metabolism

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The brain is normally responsible for consumption of 20% of total body oxygen. Most of cerebral oxygen consumption (60%) is used in generating adenosine triphosphate (ATP) to support neuronal electrical activity (Figure 25–1). The cerebral metabolic rate (CMR) is usually expressed in terms of oxygen consumption (CMRo2), which averages 3–3.8 mL/100 g/min (50 mL/min) in adults. CMRo2 is greatest in the gray matter of the cerebral cortex and generally parallels cortical electrical activity. Because of the relatively high ...

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