Nonvolumetric methods of detecting impaired intracranial compliance or reactivity: pulse width and wave form analysis

The authors have attempted to find a clinically reliable method of measuring intracranial pressure (ICP) compliance or reactivity that does not require volumetric manipulation. An analysis was undertaken of ICP, pulse widths and of the presence or absence of B waves, both experimentally in dogs and clinically in postoperative human patients. In both dogs and humans, ICP pulse width generally increased with increasing ICP and with increasing intracranial mass, and definitely increased with systolic arterial blood pressure. Nonetheless, ICP pulse width commonly failed to increase with increasing cerebral reactivity, and low ICP pulse width measurements were at times recorded in distinctly pathological situations. From the clinical study it was found that B waves were encountered more commonly in patients with increased ICP or increased ICP pulse width. However, the correlation between B waves alone or in combination with increased ICP or ICP pulse width and quantitative measurements of ICP reactivity was not significant. Mean reactivity and the range of reactivity measurements were almost identical in patient groups with and without B waves. For the time being the "ICP reserve test" remains the most accurate, the safest, and the most clinically useful method of quantitating ICP reserve.