BRAIN-TISSUE OXYGEN, CARBON-DIOXIDE, AND PH IN NEUROSURGICAL PATIENTSAT RISK FOR ISCHEMIA

A sensor that measures oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH was evaluated in brain tissue of patients at risk for i schemia. The sensor is 0.5 mm in diameter and was inserted into cortex tissue in 14 patients undergoing craniotomy for cerebrovascular surge ry. A compromised cerebral circulation was identified in 8 of 14 patie nts by single photon emission computed tomography (SPECT) scan, cerebr al angiography, and transient ischemic episodes before surgery. Under baseline conditions with isoflurane anesthesia and normal blood gases, tissue PO2 was lower in the eight compromised compared to six noncomp romised patients (noncompromised 37 +/- 12 mm Hg, compromised 10 +/- 5 mm Hg; P < 0.05), PCO2 was increased (noncompromised 49 +/- 5 mm Hg, compromised 72 +/- 23 mm Hg; P < 0.05), and pH was decreased (noncompr omised 7.16 +/- 0.08, compromised 6.82 +/- 0.21; P < 0.05). Critical t issue values for the identification of ischemia were a PO2 of 20 mm Hg , PCO2 of 60 mm Hg, and a pH of 7.0. These results suggest that brain tissue measures of PO2, PCO2, and pH provide information on the adequa cy of cerebral perfusion in neurosurgical patients.