Brain Tissue Oxygen, Carbon Dioxide, and pH in Neurosurgical Patients at Risk for Ischemia

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Abstract
A sensor that measures oxygen pressure (PO,), carbon dioxide pressure @'co,), and pH was evaluated in brain tissue of patients at risk for ischemia. The sensor is 0.5 mm in diameter and was inserted into cortex tissue in 14 patients undergoing craniotomy for cerebrovascu- lar surgery. A compromised cerebral circulation was identified in 8 of 14 patients by single photon emission computed tomography (SPECT) scan, cerebral angiog- raphy, and transient ischemic episodes before surgery. Under baseline conditions with isoflurane anesthesia and normal blood gases, tissue PO, was lower in the eight compromised compared to six noncompromised patients (noncompromised 37 t 12 mm Hg, compro- mised 10 + 5 mm Hg; P < 0.05), Pco, was increased (noncompromised 49 + 5 mm Hg, compromised 72 +- 23 mm Hg; P < 0.05), and pH was decreased (noncom- promised 7.16 -C 0.08, compromised 6.82 Ifr 0.21; P < 0.05). Critical tissue values for the identification of ische- mia were a PO, of 20 mm Hg, Pco, of 60 mm Hg, and a pH of 7.0. These results suggest that brain tissue meas- ures of PO,, Pco,, and pH provide information on the adequacy of cerebral perfusion in neurosurgical patients. (Anesth Analg 1996;82:582-6)