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The manometric pressure of the CSF is measured at the beginning and at the end of the procedure. With the patient in the lateral decubitus position, the opening pressure of the CSF is normally 70 to 200 mm H2O. If lumbar puncture is performed with the patient in the sitting position, the CSF usually rises in the manometer to about the level of the foramen magnum but not higher. If the patient coughs, sneezes, or strains during lumbar puncture, there is usually a prompt rise in CSF pressure because of congestion of spinal veins and resultant increased pressure of the contents of the subarachnoid epidural spaces; the CSF pressure subsequently falls to the previous level.
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After determination of the initial CSF pressure, four tubes of CSF are withdrawn (usually containing 2–3 mL each) under sterile conditions. Routine CSF examination usually includes cell counts, measurement of total protein, glucose, and gamma globulin levels. Cells are usually cultured, and, when appropriate, spinal fluid electrophoresis is performed to determine whether there are oligoclonal bands. (These are present in a variety of inflammatory disorders, most notably multiple sclerosis but also neurosyphilis, subacute sclerosing panencephalitis, and some cases of viral encephalitis.)
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Table 24–1 illustrates the profile of the CSF after lumbar puncture in a number of neurologic disorders.
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Box 24–1 Essentials for the Clinical Neuroanatomist After reading and digesting this chapter, you should know and understand:
Indications and contraindications for lumbar puncture
Principles of analysis of CSF
Characteristic CSF profiles (Table 24–1)