Sunday, November 2, 2014

Opening Pressure in Children

Motivation: I thought that the magic number for lumbar puncture was 20 cm H2O - the upper limit of normal for opening pressure. I was recently measuring the opening pressure in a 10 year old with headache, and I wondered if the opening pressure limit is the same in children. After all, the space for the cerebrospinal fluid (CSF) space is differently shaped as well as the volume of the CSF present. Turns out amazingly that this issue was addressed only in 2010 in a New England Journal publication.

Paper:  Avery, RA, Shah, SS, Licht, DJ, et al. Reference Range for Cerebrospinal Fluid Opening Pressure in Children. NEJM (2010) 363: 891-893.

Methods: A 2 year prospective study of CSF opening pressure in children between ages 1 to 18 without signs or symptoms of raised intracranial pressure or diseases which might change the opening pressure such as meningitis. The study was conducted at Children's Hospital of Philadelphia.

Results: In total, 197 children met inclusion criteria. The 90th percentile for opening pressure was 28 cm H2O while the 10th percentile was 11.5 cm H2O. Age was not correlated with increased opening pressure. Variables correlating with increased pressure included moderate to deep sedation (p = 0.002) and higher BMI (weak correlation, coefficient = 0.313). For children who were not sedated, the 90th percentile for opening pressure was 25 cm H2O.

Discussion: Compared to adults, the opening pressure for children is likely higher, and when interpreting lumbar puncture results, mildly elevated opening pressure of 25 cm H2O should not be called abnormal. There are a few questions raised by these findings though. Why is the opening pressure in general higher for children? Is it from decreased circulation space or increased relative volume of CSF? Also, I do not understand why sedation, which in general is a relaxant, should increase the opening pressure rather than decrease it. Answers to these questions may be important in management of increased intracranial pressure in children.