Objective B wave analysis in 55 patients with non-communicating and communicating hydrocephalus.

BACKGROUND B waves, slow and rhythmic oscillations in intracranial pressure (ICP), are claimed to be one of the best predictors of outcome after surgery for normal pressure hydrocephalus (NPH). OBJECT To determine the relation between the percentage of B waves and outcome in patients with hydrocephalus, and also the diurnal variation of B waves. METHODS ICP and patient behaviour were recorded overnight (17 to 26 hours) in 29 patients with non-communicating hydrocephalus and 26 with NPH. The B wave activity, measured with an amplitude threshold of 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, and 5.0 mm Hg, was estimated as the percentage of total monitoring time (% B waves) using a computer algorithm, and correlated with postoperative outcome, defined as changes in 12 standardised symptoms and signs. RESULTS There was no linear correlation between improvement after surgery in the 55 patients and total % B waves, but a correlation was found between improvement and % B waves during sleep (r = 0.39, p = 0.04). The percentage of B waves was the same during sleep and wakefulness, and patients with NPH had the same proportion of B waves as the non-communicating patients. CONCLUSIONS B waves are commonly observed in patients with both communicating and non-communicating hydrocephalus, but are only weakly related to the degree of postsurgical improvement.