Article
Changes in cortex oxygen distribution during an epidural mass lesion in rodents
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Published: | September 16, 2010 |
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Objective: The measurement of brain parenchyma pO2 is a valuable standard procedure for neurocritically ill patients. Here we utilize a opto-chemical method of planar oxygen detection for measuring changes of cortex pO2 during a reversibly introduced epidural mass lesion.
Methods: 17 male wistar rats (m = 303±21 g) were sedated (midazolam, fentanyl, medetomidin), intubated and ventilated. A 2*2 mm cortical window was prepared with a translucent porphyrine containing sensor foil. The sensor was excited by short light pulses (λ = 405 nm) and it’s pO2 dependant light emissions were recorded with a CCD camera of the measurement device (Biocam, Regensburg). A balloon device, which allowed to trigger an epidural mass lesion was placed over the contra lateral hemisphere. Throughout the experiment, the balloon was inflated up to an ICP of approx. 40 mmHg for 60 minutes and then deflated. ICP, RR, body temperature, EEG and cortex pO2 were recorded and blood gas samples were drawn.
Results: ICP increased from a baseline of 5,3±3,5 mmHg to 39,9±14,7 mmHg (p<0,001) due to the balloon inflation. Cortical surface pO2 over arterioles changed from 51,8±10,7 mmHg to 42,1±10,8 mmHg (p<0,001), over venoles from 41,2±7,4 mmHg to 35,4±8,8 mmHg (p<0,001) and over parenchyma (defined as area without visible vessels) from 32,9±6,0 mmHg to 29,9±5,1 mmHg respectively (p<0,001). Arterial pO2 (mean 176 mmHg) and pCO2 (mean 41,8 mmHg) remained constant (p>0,05).
Conclusions: In this animal model, a moderate epidural mass lesion causes significant decrease in cortical pO2. The parenchyma shows the smallest, although still significant pO2 changes. This may reflect autoregulative processes. The measurement system utilized here proves to be suitable for the simultaneous pO2 measurement of distinct anatomical structures of the cortex under pathophysiological conditions and may be useful as a monitoring device.