A Comparison Between Proximal and Distal Cerebrospinal Fluid Sampling Sites in Patients With External Ventricular Drains

BACKGROUND AND OBJECTIVES: Routine cerebrospinal fluid (CSF) sampling in patients with external ventricular drains (EVDs) is a standard neurosurgical practice to screen for infections and steer CSF diversion management. Although proximal CSF sampling (through CSF aspiration from the tubing) permits analysis of fresh intraventricular CSF, it carries a risk of iatrogenic infection, hemorrhage, and catheter blockage, contrary to distal CSF sampling (collected passively from the fluid chamber). This study assesses the agreement in CSF characteristics obtained through proximal and distal sampling in EVD patients. METHODS: An open, prospective, monocentric study was conducted between January 2022 and December 2023. All patients undergoing EVD placement were eligible. CSF was sampled twice weekly until EVD removal as per routine institutional practice. Samples were obtained synchronically proximally and distally. The primary end point was the agreement between sampling methods of the white cell count as quantified using the intraclass correlation (ICC), the within SD, and mean absolute difference. Secondary end points were the intermethod agreement of lactate, glucose, total protein, and microbial culture and the evaluation of the agreement over time. RESULTS: Sixty-one patients (2 × 197 samples) were analyzed. An ICC of 0.731 (95% CI: 0.650-0.796) was observed for white blood cell counts between proximal and distal samples. Microbial culture results showed perfect agreement. Strong ICCs were found for lactate (0.966), glucose (0.822), and total protein (0.910). These relations were maintained over time (>4 weeks). Although there were a relatively small number of infectious samples (n = 10), study strengths were the real-world setting, inclusion of all ages and etiologies, and longitudinal sampling over time. CONCLUSION: Distal CSF sampling is a reliable alternative to proximal CSF sampling, with a good ICC for white blood cell count; an excellent ICC for lactate, glucose, and protein; and a perfect ICC for culture, even in EVDs >4 weeks in place.