The effect of lower-extremity position on cerebrospinal fluid pressures.

OBJECTIVE: To determine the effects of lower-extremity positioning on cerebrospinal fluid opening pressure (CSFp). The authors believed that during lumbar puncture (LP), CSFp does not meaningfully decrease when the lower extremities are extended from flexion, as is often suggested. METHODS: In a convenience sample of adult patients who clinically required LP in an urban emergency department, three sequential CSFp measurements were obtained in either sequence A (knee, hip, and neck flexion [90 degrees ], then extension, then flexion) or sequence B (extension, flexion, then extension) prior to CSF withdrawal. The neck was flexed at 30 degrees when the lower extremities were flexed, while the thoracolumbar spine was kept in the neutral position for all measurements. RESULTS: Nineteen patients were studied in each sequence. Although variable, overall within-patient changes between positions were not clinically meaningful. Mean and 95% confidence intervals (95% CIs) for the decrease in CSFp from position 1 to position 3 (same position) were 0.2 cm H(2)O (1.7%) and 0.9 to -0.6 cm H(2)O (6% to -2.7%), respectively. Changing from flexion to extension decreased pressure measurements by a mean of 0.9 cm H(2)O (2.5%) [95% CI = 2.1 to -0.1 cm H(2)O (7.6% to -2.4%)]. Changing from extension to flexion increased CSFp by a mean of 1.1 cm H(2)O (6.1%) [95% CI = 0.2 to 2.0 cm H(2)O (1.3% to 11.5%)], a statistically but not clinically meaningful change. CONCLUSIONS: Changing lower-extremity position did not meaningfully change mean CSFp. These data do not support the common suggestion that extending the lower extremities during LP meaningfully decreases CSF opening pressures.