1322. Pediatric Lumbar Puncture Opening Pressures versus Intracranial Pressures: Examination of “Normal” Pressure and Misinterpretation

Authors: Christina Sarris, MD; Tyler Cole, MD; Ruth Bristol, MD (Phoenix, AZ)

Lumbar puncture remains a common pediatric procedure to measure intracranial pressure, despite considerable discussion of how various aspects of the procedure and measurements influence accuracy and interpretation.

We conducted a literature search to identify works outlining the history of pediatric LP and correlation with ICP, as well as interpretation of pressure measurements.

The first opening pressure measurement was performed by Dr. Quincke in 1891; his subsequent descriptions of performing an LP on a child with chronic headache and macrocephaly led to the first definition of normal pediatric ICP as 4-6 cm H2O. Decades passed, with few documented studies for how normal pressure was determined. Pressures were traditionally recorded in fluid scales of cm H2O, with the pediatric literature endorsing values <20 cm H2O as normal until a 2010 large prospective study deemed normal as measurement <28 cm H2O. Conversely, ICPs have traditionally been recorded in mm Hg, with a general acceptance of normal as < 20 mm Hg.  

Several 21st century studies demonstrated that LP significantly overestimates pediatric ICP and highlight variables such as BMI, depth of sedation, and sedation medication as factors that can result in increased LP opening pressure.

Critical care literature has demonstrated that most physicians use mmHg and cm H2O interchangeably. As 1 mmHg = 1.36 cm H2O, physicians may misinterpret results and provide incorrect therapeutic interventions based on these values if conversion is not performed. While this may not readily seem to be of consequence, an opening pressure of 26 cm H2O in a child may be misinterpreted as pathologic, while in reality it is a normal ICP of 19 mm Hg.

Opening pressure must be interpreted in context of other clinical findings. It is critical to recognize which fluid scales are utilized to correctly interpret pressure measurements and provide therapeutic interventions.