Abstract
BACKGROUND: Care of brain-injured patients in intensive care units has focused on maintaining arterial blood pressure and intracranial pressure within prescribed ranges. Research suggests, however, that the dynamic variability of these pressure signals provides additional information about physiological functioning and may reflect adaptive capacity. OBJECTIVES: To see if long-term outcomes can be predicted from variability of arterial blood pressure and intracranial pressure in patients with aneurysmal subarachnoid hemorrhage. METHODS: Arterial blood pressure and intracranial pressure were monitored continuously for 4 days in 90 patients (74% women; mean age, 53 years) in an intensive care unit after subarachnoid hemorrhage. Variability of arterial blood pressure and intracranial pressure signals was calculated on 4 timescales: 24 hours, 1 hour, 5 minutes, and the difference of sequential 5-second means. The Extended Glasgow Outcome Scale was used to assess functional outcome 6 months after subarachnoid hemorrhage. RESULTS: Pressure variability was better than mean pressure levels for predicting 6-month functional outcome. When initial neurological condition was controlled for, greater faster variability (particularly 5-second) was associated with better outcomes (typical P<.001), whereas greater 24-hour variability was associated with poorer outcomes (typical P<.001). CONCLUSIONS: The relationship between long-term functional outcome and variability of arterial blood pressure and intracranial pressure levels depends on the timescale at which the variability is measured. Because it is associated with better outcome, greater faster variability may reflect better physiological adaptive capacity.