Multiparametric monitoring of rat brain retraction

Neurosurgical procedures often involve the use of brain retractors (BR) although the risk of dysfunction is well appreciated. There is no efficient tool for continuous monitoring of the effects of the retraction on the tissue, which may alert the surgeon in real time. This study aims to use the Multiprobe Assembly (MPA) in real-time, in order to monitor the brain underneath the MPA, exposed to local pressure. The MPA, which combines Laser Doppler Flowmetery, NADH redox state fluorometry, EEG, Extracellular K⁺ measurement and an ICP sensor, was positioned on exposed cortex of rats, and controlled pressure was applied by a micromanipulator. The experimental BR state (pressure application at three levels) was monitored for 30 minutes, then recovery was monitored for 2 hours. Many animals exhibited damage, seen as an increase in CBF after the initial drop, and swelling of the tissue around the probe. Most animals exhibited EEG depression, transient increase of Extracellular K⁺, changes in NADH levels and DC potential, as well as development of one or more Spreading Depression waves. The study clearly observes impairment of normal brain tissue metabolism and function, due to the retraction pressure and emphasizes the need for real-time assessment of retraction effects during neurosurgical procedures.