Introduction: The BrainIT group is a collaborative network that aims to obtain high time resolution (minute by minute) physiological and clinical data from head injured patients who require intracranial pressure (ICP) monitoring. Data is anonymised and stored in an accessible database in Glasgow. We have examined the physiological data to explore the statistical features of the blood pressure recordings, compare arterial pressure values with non-invasive blood pressure readings and examine the diurnal variations in intracranial pressure.
Materials and methods: The physiological data from the first 200 validated patients recruited to the BrainIT study were examined. A total of 1.8*106 measurements of arterial and intracranial pressure (ICP) were used. Simultaneous readings of arterial pressure and non-invasive pressure were available in 16 patients from which 12 patients had a minimum of 50 valid paired readings. Intra-arterial BP and NIBP were compared per patient by Bland-Altman analysis to determine the limits of agreement and mean bias between the invasive and non-invasive data with 95% confidence.
Results: The distributions of mean, systolic and diastolic readings are close to normal with modest skewing towards higher values. There is a trend towards an increase in blood pressure with advancing age but this is not significant. Simultaneous blood pressure and ICP values suggest a triphasic relationship with a BP rising at 0.28mmHg / mmHg of ICP for ICP up to 32mmHg, 0.9mmHg / mmHg of ICP for ICP from 33 to 55mmHg and falling sharply with rising ICP for ICP over 55mmHg.
The limits of agreement between the simultaneous values if arterial pressure and non-invasive blood pressure ranged from ±11mmHg to ±37mmHg around the mean bias, the widest limits being observed in systolic pressure and the narrowest in diastolic. In half of the patients the limits are wider than ±15mmHg for all three values, diastolic, mean and systolic.
There was a trend towards a diurnal rhythm in ICP with peaks at 0900, 1600 and 2100 hours accompanied by simultaneous peaks in MAP and CPP which were very small and less than 1 mm of Hg in magnitude. This may be due to the overall attenuation of the circadian rhythms in severe head injuries.
Conclusions: The BrainIT dataset provides a rich source of data for analysis and hypothesis testing. The examination of blood and intracranial pressure records demonstrate: 1)Patients with head injury appear to have a near normal distribution of blood pressure readings that are skewed towards higher values and the relationship between BP and ICP may be triphasic; 2) measurements of intra-arterial and non-invasive blood pressure measurements made during critical care monitoring of head-injured patients do not agree well; 3) there are small diurnal variations in ICP.
Chambers IR, Mitchell P, Gregson B, Mendelow AD, on behalf of the BrainIT group. BrainIT: Examples and analyses from the data of the first 200 validated patients. British Neurosurgery Research Group meeting, Manchester. 1st-2nd February 2007.
Dr. Iain R. Chambers, Cleveland Unit, Middlesbrough. Tel: +44 (0)1642-854-778.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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