Jennifer Karen Corkrey O'Hara
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March 2008

Feature
Is My Doctor the Right One For Me?
5 important questions that can help you decide

What is essential for a good patient-doctor relationship? When is it time to re-evaluate your own relationship with a doctor?  Jerome Groopman M.D.'s book, "How Doctors Think" provides the basis for five important questions that can help you determine whether your doctor is a good fit. 
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Q & A

Q: How do I know if my opening pressure on a spinal tap is accurate?

A: To obtain an accurate opening pressure, the spinal tap must follow a certain standard procedure. Before the tap begins, you must be lying on one side with your knees slightly bent forward, a position known as lateral de cubitus. If you are in any other position, the pressure reading may not be correct. You also have to be relaxed, which means you can't hold your breath or bear down (Valsalva maneuver), because these actions can falsely elevate an opening pressure. The physician performing the tap may have you extend your legs after the needle has been inserted.

The opening pressure is simply the highest point that the cerebrospinal fluid reaches in the manometer tube. No spinal fluid should be removed until the opening pressure has been recorded. Additionally, the cerebrospinal fluid sample must not have any blood in it.

Position is one of several factors that can influence the accuracy of an opening pressure. If you are seated during the tap, for instance, the opening pressure may read higher than it actually is.

At the same time, other factors can cause an opening pressure to appear lower than it might truly be. These include the use of Diamox and possibly other drugs, as well as VP shunts. A recent tap can affect the accuracy of the opening pressure of a second tap, if done shortly after the first, because sometimes a small spinal fluid leak can develop and temporarily lower pressure. Additionally, if two spinal taps are performed close together, the spinal fluid may not have had enough time to regenerate to its hypertensive state.

Spinal fluid pressure also fluctuates, rather than remaining at one static level. Research has shown that both blood and intraocular (within the eye) pressure fluctuates with the time of the day, which is known as diurnal variation. Is this true of spinal fluid, as well? If so, it could be another factor to be considered when reading an opening pressure.

Jan. 15, 2008       GIVE A GIFT

FYI:  Jennifer's intracranial pressure last measured before her 11th surgery was over 310mmH2O.  A normal brain's intracranial pressure is approximately 100mmH2O.

What is IH?

Intracranial hypertension literally means that the pressure of cerebrospinal fluid (CSF) within the skull is too high. “Intracranial” means “within the skull.” “Hypertension” means “high fluid pressure.” To understand how this happens, it’s helpful to look at the basic anatomy of the brain and skull, as well as the process in which cerebrospinal fluid is created and absorbed.

Cerebrospinal fluid is one of three major components inside the skull; the other two are the blood supply (the arteries and veins known as the vasculature) that the brain requires to function and the brain itself. Under normal circumstances, these components work together in a delicate balance. A pressure and volume relationship exists between CSF, the brain and the vasculature. But since the skull is made of bone and cannot expand, an increase in the volume of any one component is at the expense of the other two components. For example, if the brain swells and becomes enlarged, it simultaneously compresses blood vessels, causing the sub-arachnoid space to fill with more spinal fluid. This results in an increase in intracranial pressure (i.e. cerebrospinal fluid pressure), as well as a decrease in blood flow.

CSF has several important functions. It cushions the brain within the skull, transports nutrients to brain tissue and carries waste away. CSF is produced at a site within the brain called the choroid plexus, which generates about 400-500 ml. (one pint) of the fluid each day or approximately 0.3 cc per minute. (The total volume of CSF in the skull at any given time is around 140 ml. That means the body produces, absorbs and replenishes the total volume of CSF about 3-4 times daily.) 

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Cerebrospinal fluid flows from the choroid plexus through the brain’s four, interconnecting ventricles before finally entering the sub-arachnoid space, which surrounds the brain and spinal cord. The fluid then flows over the brain and spinal cord and is eventually absorbed into the venous blood system through tiny, one-way channels called arachnoid granulations or villi. 

When this continuous cycle of CSF production, circulation and absorption functions normally, it regulates the volume of CSF in the skull and the fluid pressure remains at a constant level. In other words, the CSF production rate remains equal to the CSF absorption rate. 

But when the body cannot effectively absorb or drain CSF, intracranial pressure increases within the fixed space of the skull. And since the brain and the vasculature can only be compressed so far, intracranial pressure must rise. Intracranial hypertension in adults is generally defined as intracranial pressure that reaches 250mmH2O or above.