Flow rate of CSF through a spinal needle can accurately predict intracranial pressure in cryptococcal meningitis.

BACKGROUND: Patients with HIV-associated cryptococcal meningitis (CM) commonly present with raised intra-cranial pressure (ICP). Aggressive management of raised ICP reduces mortality but requires manometers which are unavailable in most resource-limited settings. The law of Poiseuille states that the rate of flow of liquid through a tube is directly proportional to the difference in pressure between each end and it may be possible to indirectly determine ICP by measuring flow of CSF through a spinal needle rather than using a manometer.

METHODS: A convenience sample of CM patients requiring lumbar puncture (with 22G spinal needle) for ICP measurement and control were enrolled. ICP was first measured using a narrow bore manometer. After removing the manometer the number of drops of CSF flowing from the spinal needle in 15 seconds was counted.

RESULTS: Thirty-two patients had 89 lumbar punctures performed (range 1-23). Fifty-four had high opening pressure with a CSF flow rate of 16-200 drops/ minute and 35 were normal pressure with a CSF flow rate of 8 - 140 drops/minute. Area under the fitted ROC curve was 0.89. A flow rate cut-off to define high pressure of ≥40 drops per minute correctly classified 75 of 89 lumbar punctures (accuracy 84%).

CONCLUSIONS: It's technically feasible to indirectly estimate CSF pressure to an accuracy that is clinically useful by counting drops of CSF flowing from a spinal needle. The optimal cut-off value for defining high pressure using a standard 22G spinal needle is ≥40 drops per minute. These findings have the potential to improve CM management in resource-limited settings.