MEASURING ICP AND CBF Thinking inside the box… Dr Hannah Rose SpR Eastbourne April 2007

Why do we measure ICP and CBF? Raised ICP and Low CBF = POOR outcome following brain injury Need continuous monitoring – albeit no evidence to suggest better outcome with ICP monitoring 28 Cremer OL, van Dijk GW, van Wensen E, et al. Effect of intracranial pressure monitoring and targeted intensive care on functional outcome after severe head injury. Crit Care Med 2005; 33:2207–13 (CPP=MAP–ICP)

Uses Severe HI SAH – hyperaemia vs vasospasm CVA Intracerebral haematoma Meningitis Encephalitis Perioperative Neurosurgical patients Carotid Endarterectomy

Methods Intracranial Pressure Monitors Transcranial US doppler Intraventricular Intraparenchymal Subdural Transcranial US doppler Jugular Bulb Oximetry Near Infra-red Spectroscopy Invasive Brain Tissue Oximetry Microdialysis

ICP Monitoring N = 7-15 mm Hg (Supine) Infants 1.5-6/ Child 3-7 ICP= pulsatile, changes with respiratory and cardiac cycles >15 mmHg = Pathological >15mmHg in Benign path = Rx >20-25 in Severe HI = Rx No consensus….. Not necessarily uniform distribution of ICP Also no consensus on ideal CPP in HI

Intraventricular ICP monitoring GOLD standard Measure and Rx Raised ICP Infection risk 6-11% Difficult to place in swollen brains! Reference pt = External auditory meatus (Foramen of Munro)

ICP Monitoring Alternatives Intraparenchymal Low infection risk Zero drift and calibration problems Strain gauge or fibre optic catheter tips Resistance change or change in reflection of light beam sensed with change in ICP Measures local pressures Subdural, epidural – Inaccurate

ICP waveforms - Lundberg A waves – plateau waves – steep ^ICP for 5-20mins. Always pathological. Intact autoregulation. Decreased intracranial compliance B waves – related to change in vascular tone. 0.5-2/min C waves – little significance. Oscillations 4-8/min Refractory intracranial hypertension- when ICP increases over a few hours to very high values and leads to the death of the patient unless aggressive measures such as craniectomy are instituted

CBF monitoring Transcranial Doppler Monitoring Easy to use, noninvasive, repeatable Measures basal cerebral bld flow velocity flow via doppler equation Used to differentiate vasospasm from hyperaemia (Lindegaard Index)

Jugular Bulb Oximetry Base of skull-level C1/C2 Aspiration port +/- sats probe N sats 55 – 71% Dep on paO2, CBF and O2 extraction  = hyperaemia / shunt d/t raised ICP  = Hypoxia, low CBF, Increased ICP or seizures/pyrexia Limitations: accuracy, frequent recalibrations, local complications, no focal info, rapid aspirations

Near-infrared Spectroscopy Infrared light with a shallow and deep detector Difference in absorption d/t brain Beer-Lambert Law related algorithm displays oxy/deoxy Hb conc’s Research only at present Significant errors

Invasive Brain Tissue Oximetry Measure brain oxygen levels directly Licox (Clark Electrode) Neurotrend ( ‘Fluorescent Quenching -> T, pO2,pCO2, pH) Measure local changes in oxygenation missed by SjO2 ? Role---multimodal Rx

Microdialysis Intracerebral fine coaxial catheter Low flow dialysis fluid through catheter Fluid removed regularly and analysed Energy related substances (glu,lac,pyr,aden,xan) Neurotransmitters (glut,asp,GABA) Tissue damage markers (glyc,K,cytokines) Exogenous substances (drugs)  lactate/pyruvate = tissue ischaemia Research only at present

Further Reading L. A. Steiner and P. J. D. Andrews Monitoring the injured brain: ICP and CBF Br. J. Anaesth. 2006 97: 26-38; doi:10.1093/bja/ael110 K Pattinson, G Wynne-Jones and C Imray Monitoring intracranial pressure, perfusion and metabolism Continuing Education in Anaesthesia, Critical Care and Pain, Vol 5 No 4 2005