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Effects of Prone Position and Positive End-Expiratory Pressure on Noninvasive Estimators of ICP: A Pilot Study
Chiara Robba1, Nicola Luigi Bragazzi, Alessandro Bertuccio
1*Neurosciences Critical Care Unit, Addenbrooke's Hospital, Cambridge, United Kingdom ∥Brain Physics Laboratory, Department of Clinical Neurosciences, Division of Neurosurgery, Cambridge Biomedical Campus, University of Cambridge, Cambridge §Division of Neurosurgery, Department of Clinical Neurosciences, S.George Hospital, University of London, London, UK Departments of #Neurosurgery †Intensive Care, Galliera Hospital ‡Department of Health Sciences (DISSAL), School of Public Health, University of Genoa, Genoa, Italy ¶Department of Medicine, Division of Critical Care Medicine, Vancouver General Hospital, Vancouver, BC, Canada.
Background:
Prone positioning and positive end-expiratory pressure can improve pulmonary gas exchange and respiratory mechanics. However, they may be associated with the development of intracranial hypertension. Intracranial pressure (ICP) can be noninvasively estimated from the sonographic measurement of the optic nerve sheath diameter (ONSD) and from the transcranial Doppler analysis of the pulsatility (ICPPI) and the diastolic component (ICPFVd) of the velocity waveform.
Methods:
The effect of the prone positioning and positive end-expiratory pressure on ONSD, ICPFVd, and ICPPI was assessed in a prospective study of 30 patients undergoing spine surgery. One-way repeated measures analysis of variance, fixed-effect multivariate regression models, and receiver operating characteristic analyses were used to analyze numerical data.
Results:
The mean values of ONSD, ICPFVd, and ICPPI significantly increased after change from supine to prone position. Receiver operating characteristic analyses demonstrated that, among the noninvasive methods, the mean ONSD measure had the greatest area under the curve signifying it is the most effective in distinguishing a hypothetical change in ICP between supine and prone positioning (0.86±0.034 [0.79 to 0.92]). A cutoff of 0.43 cm was found to be a best separator of ONSD value between supine and prone with a specificity of 75.0 and a sensitivity of 86.7.
Conclusions:
Noninvasive ICP estimation may be useful in patients at risk of developing intracranial hypertension who require prone positioning.
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