Estimation of cerebrospinal fluid compensation parameters in hydrocephalus using short-lasting constant rate lumbar infusion tests.

OBJECTIVES: The lumbar infusion test is an invasive technique for quantifying cerebrospinal dynamics in patients with hydrocephalus. However, some patients have difficulty tolerating the duration of this procedure. Therefore, we investigated the limits of shortening the test by examining the reliability of cerebrospinal fluid (CSF) compensatory parameters as a function of time. METHODS: We analysed recordings of the intracranial cerebral pressure (ICP) response to a constant, high-rate infusion of saline (2 ml/min) lasting 5.7-20 (12 ± 10) min in 30 patients with a preliminary diagnosis of hydrocephalus (13 men, aged 37-81 [65 ± 10] years). We performed computerised identification of CSF outflow resistance (R(out)), intracranial compliance parameters: elastance index (E) and reference pressure (P(0)), based on the truncated ICP response (20-100% of the available test length), estimating either all three parameters (3p method) or only R(out) and E (2p method) assuming P(0) as the regression between the ICP and its amplitude. RESULTS: Following considerable variation during the initial rise of ICP, R(out) typically converged within ± 10% of their final values within 10-15 min. Final R(out) values were 4-40 (12 ± 6) mmHg/ml/min, and were method independent (R(2) = 0.97). Compliance parameters (E, typically 0.1-0.5/ml; P(0): - 10 to + 20 mmHg) agreed poorly between methods (R(2) = 0.3-0.7) and varied considerably within the observed infusion periods. CONCLUSION: The lumbar infusion test may be shortened to 10-15 min using a rapid infusion rate of 2 ml/min that fulfils the primary objective of obtaining reliable estimates of R(out). This may benefit patients who do not tolerate the full procedure.