TY - CHAP M1 - Book, Section TI - Neurophysiology & Anesthesia A1 - Butterworth IV, John F. A1 - Mackey, David C. A1 - Wasnick, John D. PY - 2018 T2 - Morgan & Mikhail's Clinical Anesthesiology, 6e AB - KEY CONCEPTS Cerebral perfusion pressure is the difference between mean arterial pressure and intracranial pressure (or central venous pressure, whichever is greater). The cerebral autoregulation curve is shifted to the right in patients with chronic arterial hypertension. 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 to 2 mL/100 g/min per mm Hg change in PaCO2. CBF changes 5% to 7% per 1°C change in temperature. Hypothermia decreases both cerebral metabolic rate and CBF, whereas pyrexia has the reverse effect. 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. The blood–brain barrier may be disrupted by severe hypertension, tumors, trauma, strokes, infection, marked hypercapnia, hypoxia, and sustained seizure activity. 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. With the exception of ketamine, all intravenous agents either have little effect on or reduce cerebral metabolic rate and CBF. With normal autoregulation and an intact blood–brain barrier, vasopressors increase CBF only when mean arterial blood pressure is below 50 to 60 mm Hg or above 150 to 160 mm Hg. The brain is very vulnerable to ischemic injury because of its relatively high oxygen consumption and near-total dependence on aerobic glucose metabolism. Hypothermia is the most effective method for protecting the brain during focal and global ischemia. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/03/28 UR - accessanesthesiology.mhmedical.com/content.aspx?aid=1161429381 ER -