Neuromonitoring, Neuroimaging, and Neurocritical Care Procedures
Neuromonitoring, Neuroimaging, and Neurocritical Care Procedures
Invasive ICP monitoring-external ventricular drain (EVD) or parenchymal monitor-guides therapy when the neurologic exam is unreliable. The EVD is also therapeutic for hydrocephalus. Zero the transducer at the level of the foramen of Monro (tragus); never flush an EVD. Complications include hemorrhage, infection, and malfunction. ICP waveforms: P1 is the arterial percussion wave, P2 the tidal wave, P3 the dicrotic wave. A P2 taller than P1 suggests poor intracranial compliance and impending herniation.
Other monitors include brain tissue oxygen (PbtO2), jugular venous oxygen saturation, transcranial Doppler for vasospasm, continuous EEG for nonconvulsive seizures and burst suppression, and pupillometry. Neuroimaging: noncontrast CT for hemorrhage and herniation; CTA for large-vessel occlusion and aneurysm; CT perfusion and MRI (diffusion-weighted imaging with perfusion mismatch) help identify salvageable tissue; MRI is useful for posterior fossa, spinal cord, and early ischemia.
Procedures: ultrasound-guided central line placement, arterial line, lumbar puncture after imaging when safe, tracheostomy timing, and bronchoscopy. For EVD sampling, use sterile technique; do not routinely change catheters. Sedation interruption and daily neurologic exams are important but weigh against ICP instability.
Traps: interpreting a high ICP alone without checking transducer level and waveform; ordering MRI in an unstable patient; missing a delayed epidural hematoma after a negative initial CT; and treating an EVD as a routine line without infection precautions.
Worked example: an ICP waveform showing P2 > P1 with a rising ICP trend warrants urgent treatment-head elevation, sedation, osmotherapy-and repeat imaging, even if the numeric ICP is only modestly elevated.