Objectives Lumbar Puncture opening pressure in lateral decubitus has been considered the gold standard method of intracranial pressure (ICP) measurement for many years. The use of continuous intraparenchymal ICP monitoring is more recent and there is no consensus regarding what can be considered normal ICP with this method of measurement. A conversion factor between lumbar puncture opening pressure and 24 hours ICP monitoring could provide a better insight on the interpretation of ICP. This study investigates the differences between 24 hours ICP and ICP in lumbar puncture position.

Design Single centre prospective observational study.

Subjects Fifty-four patients (42F:12M, mean age 38±12 years) were included.

Methods Patients investigated with 24 hours ICP monitoring who underwent a short exercise battery during the monitoring period were included. The exercise battery was standardised; patients were asked to stay in a supine, sitting, standing and lumbar puncture position for 2 min each.Mean ICP and pulse amplitude were calculated for each position.

Results The mean 24 hours ICP was 4.9 mmHg (±6.9 SD) and the mean ICP in lumbar puncture position was 14.1 mmHg (±8.9 SD). The average increase in lumbar puncture position was 9.1 mmHg (±5.9 SD). Patients with normal lumbar puncture position ICP (<12 mmHg) had an average 24 hours ICP of 1.4 mmHg (±2.81 SD).

Conclusions Our results suggest that ICP measured in lumbar puncture position is on average 9.1 mmHg higher than 24 hours ICP results. Larger studies will be needed to confirm these findings.