Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content ++Table Graphic Jump Location|Download (.pdf)|PrintCranial contentsSkull represents a closed, non-expandable unit containing three compartments (CBV, CSF, brain tissue) determining ICPAny increase in volume of one of the cranial compartments must be compensated by a decrease in volume of another to maintain the pressure equilibrium (Monro-Kellie doctrine)Small increases in intracranial volume will lead to large increases in ICP once this buffer mechanism is exhausted (Figure 101-1), compromising CBVBlood and cerebral vasculature (cerebral blood volume, CBV)Two carotid arteries (70% blood flow to the brain)Two vertebral arteries (30% blood flow to the brain)Arterial anastomosis through Willis circle and anastomosis with external carotid arteries through branches of facial and ophthalmic arteriesVenous return through cortical veins (superficial drainage), and basilar and ventricular veins (profound drainage) essentially into the IJ veinsCerebro-spinal fluid (CSF)Produced by choroid plexus, reabsorbed by granules of PacchioniTotal volume of CSF in the adult: 140–270 mLProduction of 0.2–0.7 mL/min or 600–700 mL/day++Figure 101-1. ICP as a Function of IC VolumeGraphic Jump LocationView Full Size||Download Slide (.ppt)Reproduced from Morgan GE, Mikhail MS, Murray MJ: Clinical Anesthesiology. 4th Edition. Figure 25-5. Available at: www.accessmedicine.com. Copyright © The McGraw-Hill Companies, Inc. All rights reserved.++Table Graphic Jump Location|Download (.pdf)|PrintPhysiologic Background: Cerebral Perfusion and AutoregulationCerebral blood flow (CBF), cerebral metabolic requirement of oxygen (CMRO2), and cerebral perfusion pressure (CPP)CBF (normal: 50 mL/min/100 g of brain) is coupled with CMRO2 and determined by cerebral autoregulation and cerebrovascular reactivity to CO2Cerebral perfusion pressure (CPP) is the difference between mean arterial pressure (MAP) and ICPCerebral autoregulation is the capacity of the cerebral arterioles to maintain a relatively constant CBF by alteration of their vascular resistance (vasoconstriction over a wide range of blood pressures (between MAP of approximately 50–150 mm Hg). At the extreme limits of MAP or CPP (high or low), CBF is directly proportional to CPP (Figure 101-2)CO2 is a potent vasodilator, showing a relationship between PaCO2 (30–80 mm Hg) and CBF that is nearly linearAutoregulation and cerebrovascular reactivity to CO2 may be altered in various pathological states (TBI, severe focal ischemia, brain tumor), as well as by administration of anesthetics++Figure 101-2. Influence of PaO2, PaCO2, and MAP (Green Line) on Cerebral Blood FlowGraphic Jump LocationView Full Size||Download Slide (.ppt)Reproduced with permission from Shapiro HM. Intracranial hypertension: Therapeutic and anesthetic considerations. Anesthesiology. 1975;43:445.++Table Graphic Jump Location|Download (.pdf)|PrintInfluence of Anesthetic Agents on CBF, ICP, and CMRO2MedicationCBF and ICPCMRO2Propofol↓↓Thiopental↓↓Etomidate↓↓Ketamine↑↑Nitrous oxide↑↑Volatile anesthetics1↑↓Opioids2=Slight ↓1Do not exceed 0.8 MAC ... Your Access profile is currently affiliated with [InstitutionA] and is in the process of switching affiliations to [InstitutionB]. Please select how you would like to proceed. Keep the current affiliation with [InstitutionA] and continue with the Access profile sign in process Switch affiliation to [InstitutionB] and continue with the Access profile sign in process Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Error: Incorrect UserName or Password Username Error: Please enter User Name Password Error: Please enter Password Sign in Forgot Password? Forgot Username? Sign in via OpenAthens Sign in via Shibboleth You already have access! Please proceed to your institution's subscription. Create a free profile for additional features.