• Per Kristian Eide and Wilhelm Sorteberg.
• Department of Neurosurgery, Oslo University Hospital, Rikshospitalet, and Faculty of Medicine, University of Oslo, Oslo, Norway. peide@ous-hf.no
• Biomed Eng Online. 2013 Jan 1;12:14.

BackgroundIn an attempt to characterize the intracranial pressure-volume compensatory reserve capacity, the correlation coefficient (R) between the ICP wave amplitude (A) and the ICP (P) level (RAP) has been applied in the surveillance of neurosurgical patients. However, as the ICP level may become altered by electrostatic discharges, human factors, technical factors and technology issues related to the ICP sensors, erroneous ICP scores may become revealed to the physician, and also become incorporated into the calculated RAP index. To evaluate the problem with regard to the RAP, we compared simultaneous RAP values from two separate ICP signals in the same patient.Materials And MethodsWe retrieved our recordings in 20 patients with cerebral bleeds wherein the ICP had been recorded simultaneously from two different sensors. Sensor 1 was always a solid sensor while sensor 2 was a solid sensor (Category A), a fluid sensor (Category B), an air-pouch sensor (Category C), or a fibre-optic sensor (Category D). The simultaneous signals were analyzed with automatic identification of the cardiac induced ICP waves, with subsequent determination and comparison of the Pearson correlation coefficient between mean wave amplitude (MWA) and mean ICP (RAP) for 40 6-s time windows every 4-min period.ResultsA total of 23,056 4-min RAP observations were compared. A difference in RAP≥0.4 between the two signals was seen in 4% of the observations in Category A-, in 44% of observations in Category B-, in 20% of observations in Category C-, and in 28% of observations in Category D patients, respectively. Moreover, the combination of a RAP of <0.6 in one signal and ≥0.6 in the other was seen in >20% of scores in 3/5 Category A-, in 3/5 Category B-, in 5/7 Category C- and 1/3 Category D patients.ConclusionsSimultaneous monitoring of the ICP-derived index RAP from two separate ICP sensors reveals marked differences in the index values. These differences in RAP may be explained by erroneous scoring of the ICP level. This will hamper the usefulness of RAP as a guide in the management of neurosurgical patients.

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