Article
A novel opto-chemical pO2 measurement on the cortex in comparison with the intraparenchymal Licox-probe
Vergleich einer neuen opto-chemischen pO2-Messung an der Kortexoberfläche mit der intraparenchymalen Licox-Sonde
Search Medline for
Authors
Published: | May 30, 2008 |
---|
Outline
Text
Objective: The measurement of the brain tissue pO2 is an important component of the neuromonitoring of critically ill patients with SAH or TBI. Here we compare the typical intraparenchymal pO2 measurement with a novel opto-chemical measurement on the cortex surface. The Method is based on oxygen dependant luminescence quenching of a porphyrine dye in the sensor foil.
Methods: The measurement device (prototype, Biocam, Regensburg) was placed after a craniectomy on the cortex of intubated and ventilated wistar rats (n=6, m=355±27g). The sensor foil is excited by LED light flashes; the luminescence of the foil and also normal images of the measurement area are detected by a CCD-camera, which is coupled to the foil via a NMDA cylinder. The data is processed with PC software (IDL, Creaso). Regions of interest were defined over a cortical vein, an arteriole and the parenchyma. A Licox-probe was placed in the frontal cortex of the opposite side. Arterial pO2 and pCO2 were varied by changing FiO2 and ventilation settings. Blood gas values, arterial pressure, heart rate and brain pO2 were recorded simultaneously.
Results: The intraparenchymal (Licox) pO2 correlated at best with the pO2 over the cortex parenchyma (correletation coefficient =0,55; p<0,001; n=93). Correlations with the pO2 over veins (c.c.=0,36; p<0,001) and arterioles (c.c.=0,24; p<0,05) were weaker. The correlation coefficient of the arterial pO2 (paCO2 33-47 mmHg) with the Licox-measures was 0,37 (p<0,001), and with the cortical pO2 it was 0,75 (arteriole, p<0,001), 0,73 (vein, p<0,001) und 0,37 (parenchyma, p<0,001). Variation of paCO2 (n=54, paO2 70-130 mmHg) had no effect on the Licox measures (c.c.=-0,06, p=0,68) and small influence on the cortex pO2 (vein: 0,04, p=0,76; arteriole: 0,30, p<0,05, parenchyma: 0,28, p<0,05).
Conclusions: The two dimensional pO2 detection on the cortex surface allows differentiated and simultaneous measurements of the anatomical structures. The Licox measurement in the white matter correlated most of all with the pO2 over the cortex parenchyma. The cortical measurement provides additional pO2 values of arterioles and veins. The oxygenation of these vessels as well as probable drops in the cortex pO2 may not be detected by the intraparenchymal pO2 probe.