Slope of the intracranial pressure waveform after traumatic brain injury.

Background: The measurement and treatment of ICP within the management of TBI generally focuses on keeping the mean ICP to less than 20 mm Hg. More sophisticated analysis of the intracranial pressure waveform has yielded important relationships, but those methods have not gained widespread use. Prior analysis of the slope of the ICP waveform during inspiration and expiration in patients with hydrocephalus has provided valuable information that has never been applied to patients with TBI. This study used digital methods to examine ICP and the slope of the ICP waveform in relation to the respiratory cycle in subjects with TBI.

Methods: Intracranial pressure was monitored in 6 randomly selected patients admitted with acute TBI. In the first 3 subjects, a single 5-minute recording was analyzed. In 3 subsequent subjects, 4 nonsequential 5-minute epochs were analyzed during periods of varying ICP. The systolic slope of the ICP waveform was compared during inspiration and expiration, and then evaluated in relation to simultaneous mean ICP.

Results: The slope of the systolic ICP waveform was significantly greater during inspiration than during expiration (P < .0001 for 5 subjects and P < .03 for 1 subject). Within each subject, the ICP slope was positively correlated with simultaneous ICP (P < .0001 in all 6 cases).

Conclusion: Greater systolic ICP waveform slope during inspiration has not been described previously after TBI and is consistent with prior observations in subjects with hydrocephalus. The strong correlation between ICP slope and simultaneous mean ICP suggests that increasing ICP slope might indicate loss of intracranial compliance after TBI.