During a lumbar puncture (spinal tap) a large needle is inserted through the back and into the spinal canal to measure the pressure and collect a sample of cerebrospinal fluid (CSF). Lumbar puncture is the most reliable method to diagnose meningitis, a life-threatening but highly treatable condition. Lumbar punctures are also performed to diagnose subarachnoid hemorrhage, hydrocephalus, and idiopathic intracranial hypertension, and to inject medications into the cerebrospinal fluid, particularly spinal anesthetics and chemotherapeutics.
Opening Pressure
Measurement of CSF pressure has long been recommended as part of the lumbar puncture procedure, and is typically accomplished using a liquid column hydrostatic manometer. This device is awkward, and an assistant is needed to collect samples while the physician steadies the manometer to prevent needle dislodgement. In one study, it took nearly three minutes for the pressure to equilibrate in the manometer(1). This time adversely impacts the procedure tolerance for pediatric patients who must be held still in a curled position throughout. In many pediatric emergency rooms, manometers are not used routinely because they are so cumbersome. This loss of diagnostic information is due solely to the inadequacy of the current technique, which has not been substantively improved since it was introduced by Dr. Quincke and Dr. Wynter in 1891.
As one physician writes, “Traditional practice has been to measure CSF pressure at lumbar puncture by open ended manometry but this method is fraught with inaccuracies….eyeballing a fluctuating meniscus and the need for several pairs of hands have negated much of its usefulness(2,3).”
Another author states, “attachment and removal of the (manometer) apparatus may dislodge the needle, particularly in a moving child. It takes time for the CSF to travel up the manometer and reach a steady state before the pressure can be determined. Air bubbles in the manometer may interfere with accurate readings. Because of these problems, CSF pressure is often not measured during lumbar puncture in children(4).”
Traumatic Taps
During lumbar puncture, the physician slowly advances a needle toward the spine until a “pop” is felt. The “pop” is not always reliable, particularly in infants, and the only other way to confirm needle entry into the subarachnoid space is by visualizing return of CSF through the needle hub. CSF may take tens of seconds to appear at the end of the needle, and the needle may need repositioning multiple times, making the procedure very time consuming and uncomfortable for the patient. If the physician advances the spinal needle too far, the needle can damage the venous plexus and cause a “bloody tap” that contaminates the CSF sample and frequently leads to additional procedures. Unfortunately, nearly 20% of pediatric lumbar punctures result in a “bloody tap”(5), in part because the physician does not have a good indicator of needle location. A number of techniques have been proposed to improve lumbar puncture success and decrease the rate of traumatic taps. One technique to avoid bloody taps, early stylet removal, increases success, most likely due to earlier identification that the subarachnoid space has been reached, when CSF is seen at the end of the stylet(6,7). It is possible that early idenitifcation of the subarachnoid space by a rapid pressure reading could also decrease the frequency of bloody taps. No data exists to support this assertion, in part because a device has yet to be designed to provide a rapid pressure reading during lumbar puncture.
The Compass™ Lumbar Puncture
is a much needed update to a procedure that has undergone minimal change in the past 150 years. The Compass offers a cost effective alternative to manometry to quickly and accurately measure pressure during lumbar puncture, allowing this valuable data to be collected easily and without compromising the speed of the procedure. Learn more about the Compass LP.
