Consequence of insertion trauma – effect on early measures when using intracerebral devises.

INTRODUCTION A variety of intracerebral devices are used to quantify biological processes in cerebral tissue. Installing such a device causes an insertion trauma, which may affect early measures. Current literature proposes minimum one hour of observation before acquiring first measures by microdialysis. It is unknown whether this applies to other intracerebral devices. We therefore aimed to investigate time to reach steady state when using microdialysis and two intracerebral probes in a piglet model. MATERIAL AND METHODS 10 piglets < 24 h of age were anaesthetized. Two probes (Codman® and Oxford Optronics®) and a microdialysis catheter (CMA Microdialysis®) were installed 10 mm into the left hemisphere. Probes measured intracranial pressure, blood flow though laser Doppler, and oxygen tension. Microdialysis measured lactate, glucose, glycerol, and pyruvate. After insertion, measures were acquired hourly for 20 hours. Steady state was assessed through eyeballing of data plots. RESULTS Glucose and pyruvate reached steady state 2 hours after insertion while lactate and glycerol required 6 hours. Blood flow reached steady state after 2 hours, intracranial pressure after 5 hours, and oxygen tension after 15 hours. Inter-individual variability decreased for the majority of measurements until 6-7 hours. CONCLUSION Steady state occurred later than expected in all measures. Microdialysis and the two probes required at least 2 hours – although numerous hours was needed for some measures. Inter-individual variability also decreased over time. Consequently, sufficient observation time is crucial to obtain correct baseline values and valid comparisons between individuals.