Cerebrospinal fluid collection: a comparison of different collection sites on the external ventricular drain

Intracranial pressure monitoring using an external ventricular drainage (EVD) system is the most commonly used technology to monitor intracranial pressure or drain cerebrospinal fluid (CSF) in neurological and neurosurgical patients. CSF samples are collected routinely from the EVD system for laboratory tests. No study has been conducted to identify where the most appropriate site for CSF collection is in order to reduce the disruption of the closed EVD system and reduce the risk of infection.

The purpose of this study was to identify a CSF sampling port in the EVD system that is easily accessible, provides accurate results, and minimizes disruption to the closed EVD system.

Fifty patients admitted to the neurological and neurosurgical intensive care step-down unit with the EVD system between July 2007 and September 2009 agreed to participate in the study. There were 21 women and 29 men. Forty-seven patients' data were analyzed.

The design was quasi-experimental using a convenience sample. Two samples of CSF were collected daily. One sample was collected from the proximal port and another sample was collected from the distal port. The second sample was collected immediately after the first. Each set of samples (proximal and distal) was tested and compared for any differences in appearance, culture results, and concentrations of protein, glucose, and white cell count.

Using a two-tailed paired t test with 95% confidence interval, there was no statistically significant difference between the samples obtained from the two collection sites for protein, glucose, white cell count, appearance, and culture. Pearson's correlation coefficient was also used to analyze the correlation for the continuous measures. Both protein and glucose had very high correlations. However, the white cell count, and white cell counts and culture had very low correlations.

The distal port of the EVD system is safe and easy for CSF collection. It also provides accurate results for CSF samples. When the CSF sample is collected from the distal port, the entire volume of CSF in the drip chamber should be collected and tested to obtain an accurate WBC count per unit of volume.