Correlation of continuously monitored regional cerebral blood flow and brain tissue oxygen

Summary

Background. The purpose of this study was to investigate the relationship between continuously monitored regional cerebral blood flow (CBF) and brain tissue oxygen (P_tiO₂).

Methods. Continuous advanced multimodal neuromonitoring including monitoring of P_tiO₂ (Licox, GMS) and CBF (QFlow, Hemedex) was performed in eight patients after severe subarachnoid haemorrhage (n=5) and traumatic brain injury (n=3) for an average of 9.6 days. Parameters were measured using a flexible polarographic P_tiO₂-probe and a thermal diffusion CBF-microprobe.

Findings. Regarding the whole monitoring period in all patients, the data indicated a significant correlation between CBF and P_tiO₂ (r=0.36). In 72% of 400 analysed intervals of 30 minutes duration with P_tiO₂ changes larger than 5 mmHg, a strong correlation between CBF and P_tiO₂ existed (r > 0.6). In 19% of intervals a still statistically significant correlation was observed (0.3 < r < 0.6). During the remaining 9% no correlation was found (r < 0.3). Regarding the clinical stability of the monitoring devices, the CBF monitoring system allowed monitoring of CBF in 64% of the time when P_tiO₂ monitoring was possible only. Phases of non-monitoring were mostly due to fever of the patient, when the system does not allow monitoring to avoid overheating of the cerebral tissue.

Conclusions. This study suggests a correlation between CBF and P_tiO₂. The level of P_tiO₂ seems to be predominately determined by regional CBF, since changes in P_tiO₂ were correlated in 90% of episodes to simultaneous changes of CBF.