A catheter-tipped microtransducer (Camino ICP Bolt, or Codman
MicroSensor) can be placed into the parenchyma, epidural space, subdural
space, or ventricle. The technology makes use of the principle that increase
pressure will place greater strain on the diaphragm at the distal tip which can be
interpreted as pressure values using experimental norms. The main advantage
of this modality is decreased risk of infection or hemorrhage. Downsides of this
catheter include 1) inability to therapeutically drain and 2) measurement ‘drift’
over time (there is no way to externally re-zero the monitor once it is placed).
This drift may begin as soon as 48 hours after catheter placement, though many
intensivists argue that the vast majority of intracranial hypertensive issues occur
early in patient courses.
While the monitor allows the intensivist to adjust systemic blood pressure
to maintain CPP, this may not be indicative of stable cerebral blood flow. Indeed,
in ICH cerebral autoregulation is unreliable. Therefore, additional monitors of
cerebral oxygenation and metabolism are undergoing evaluation.
B. Monitors of Cerebral Perfusion
Jugular bulb saturation is a global marker of cerebral perfusion. It is
insensitive to small regional abnormalities in brain oxygenation and has largely
been abandoned in clinical use. Newer implantable tissue oxygen microsensors
(Integra’s Licox Brain Oxygen Monitoring System) require a catheter be placed
into the white matter. Normative values are being developed, with PbtO 2 <
10mmHg in adults being considered abnormal. Long-term outcome and