Bilateral Monitoring of CBF and Tissue Oxygen Pressure in the Penumbra of a Focal Mass Lesion in Rats

Summary

The continuous monitoring of cerebral microcirculation is aimed at preventing secondary ischemic brain damage subsequent to severe head injury. Interrelations between bilateral changes of cortical Laser Doppler Flowmetry (LDF) and intraparenchymal, subcortical p(ti)O₂ values were continuously monitored in the forebrain of rodents. A trauma group of 8 animals received an unilateral, focal parietal mass lesion by an expanding epidural balloon. 10 animals served as a sham group. In the sham-operated group the drift of median LDF values was 10.8% in the left and 9.6% in the right hemisphere. The absolute median p(ti)O₂ showed values of 31.2 mm Hg (27.9–34.9) in the left and 30.1 mm Hg (27.5–31.7) in the right hemisphere. During maximum brain compression median LDF values decreased ipsilateral to 18.6% (13.3–24.4%) and contralateral to 23.4% (17.1–56.6%) of the baseline values. P(ti)O₂ decreased ipsilateral to absolute values of 4.6 mm Hg (3.2–6.7 mm Hg) and contralateral to values of 7.1 mmHg (6.1–8.5 mm Hg). After balloon deflation cortical LDF was restored much faster but did not reach baseline values [ipsilateral 55.2% (42.6–67.8%); contralateral 67% (53.4–82%) of baseline values]. The p(ti)O₂ values reached ipsilateral 77.4% (72.0–93.3%) and contralateral 88.8% (86.0–97.4%) of baseline values. Both parameters showed a significant correlation (r = 0.57; p < 0.02). P(ti)O₂ measurements supplement on-line cortical CBF monitoring and by far outscore discontinuous alternative measurement techniques in detecting hemodynamically relevant events. The small spatial resolution of the p(ti)O₂ probes, however, which in the small animal model may be of negligible influence, does raise the question whether the values gained offer a general overview of the microcirculatory situation.