Meningitis and subarachnoid hemorrhage (SAH) are serious, life-threatening conditions. They require prompt and accurate diagnosis in the Emergency Department (ED) due to their significant morbidity and mortality.1 There are many diagnostic modalities available to the Emergency Physician (EP) to assist in the diagnosis. However, the lumbar puncture (LP) is still considered the gold standard. The LP is a procedure that is often performed in the ED to obtain information about the cerebrospinal fluid (CSF) to aid in the diagnosis of a variety of medical conditions. Knowledge about the proper indications, contraindications, various techniques, equipment, and recognition and treatment of potential complications is vital to any EP who performs this procedure. It is important to perform a thorough neurologic examination prior to the LP, as significant neurologic deficits may suggest increased intracranial pressure (ICP). Significant morbidity and mortality can result if the procedure is performed on the wrong patient.
ANATOMY AND PATHOPHYSIOLOGY
The entire cavity of the brain and spinal cord has a volume of approximately 1650 mL. CSF occupies only approximately 150 mL of this volume. The brain literally floats in the CSF because the specific gravity of the CSF and brain are approximately the same. Approximately 500 mL of CSF is produced every day. This is approximately 0.35 to 0.5 mL/min. It takes less than 20 minutes for the patient to replace the CSF removed from the LP procedure. Most of the CSF is produced by the choroid plexus within the lateral ventricles. Small amounts of choroid plexus can also be found in the third and fourth ventricles. Lesser amounts of CSF are secreted by the ependymal surfaces of the ventricles. A minimal volume of CSF is produced by the brain through the small perivascular spaces that surround the blood vessels entering the brain substance.
The flow of CSF through the ventricular system is rather simple (Figure 142-1). CSF produced in the lateral ventricles flows through the foramina of Monro into the midline third ventricle. It then passes through the aqueduct of Sylvius into the fourth ventricle. From the fourth ventricle, the CSF flows into the cisterna magna via two lateral openings (foramina of Luschka) and one midline opening (foramen of Magendie). The cisterna magna is located beneath the medulla and cerebellum. It is continuous with the subarachnoid space that surrounds the brain and spinal cord. The CSF then flows through the subarachnoid space to bathe the brain and spinal cord. The CSF is absorbed back into the venous system by way of the arachnoid villi.
CSF circulation around the brain and upper spinal cord.
The average CSF pressure is 130 mmH2O when measured in the lateral decubitus position. It can range from 70 to 200 mmH2O in a normal person ...