British Journal of Anaesthesia, 2003, Vol. 90, No. 3 291-295
© 2003 The Board of Management and Trustees of the British Journal of Anaesthesia
Clinical Investigations |
Extrapolation to zero-flow pressure in cerebral arteries to estimate intracranial pressure
1 Klinik für Anästhesiologie, Universitätsklinikum der RWTH Aachen, Pauwelsstrasse 30, D-52074 Aachen, Germany. 2 Institut für Pathophysiologie, Universitätsklinikum Essen, Germany. 3 Zentrum Anaesthesiologie, Rettungs- und Intensivmedizin, Georg-August-Universität, Göttingen, Germany. 4 Klinik für Anästhesiologie und Operative Intensivmedizin Städtische Kliniken, Oldenburg, Germany
Corresponding author. E-mail: wbuhre@ukaachen.de
Background. Cerebral perfusion pressure (CPP) is commonly calculated from the difference between arterial blood pressure (AP) and intracranial pressure (ICP). ICP can be considered the effective downstream pressure of the cerebral circulation. Consequently, cerebral circulatory arrest would occur when AP equals ICP. Estimation of AP for zero-flow pressure (ZFP) may thus allow estimation of ICP. We estimated ZFP from cerebral pressure–flow velocity relationships so that ICP could be measured by transcranial Doppler sonography.
Methods. We studied 20 mechanically ventilated patients with severe head injury, in whom ICP was monitored by epidural pressure transducers. AP was measured with a radial artery cannula. Blood flow velocity in the middle cerebral artery (VMCA) ipsilateral to the site of ICP measurement was measured with a 2 MHz transcranial Doppler probe. All data were recorded by a microcomputer from analogue–digital converters. ZFP was extrapolated by regression analysis of AP–VMCA plots and compared with simultaneous measurements of ICP.
Results. ZFP estimated from AP–VMCA plots was linearly related to ICP over a wide range of values (r=0.93). There was no systematic difference between ZFP and ICP. Limit of agreement (2 SD) was 15.2 mm Hg. Short-term variations in ICP were closely followed by changes in ZFP.
Conclusion. Extrapolation of cerebral ZFP from instantaneous AP–VMCA relationships enables detection of severely elevated ICP and may be a useful and less invasive method for CPP monitoring than other methods.
Br J Anaesth 2003; 90: 291–5
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