Effects of superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis on the cerebrospinal fluid gas tensions and pH in hemodynamically compromised patients

Purpose: This study was aimed to directly measure cerebrospinal fluid (CSF) gas tensions and pH before and after STA-MCA anastomosis for occlusive carotid artery diseases to investigate its direct effects on the ischemic brain. Methods: This study included 9 patients who underwent STA-MCA anastomosis on the basis of CBF studies. About 1 mL of CSF was collected before and after bypass procedures, and CSF pH, CSF PO₂, and CSF PCO₂ were measured with a blood gas analyzer. As the controls, the CSF was collected from 6 patients during surgery for unruptured cerebral aneurysm. CSF PO₂ and CSF PCO₂ were expressed as the ratio to PaO₂ and PaCO₂, respectively. Results: Before bypass procedure, CSF PO₂/PaO₂ was 0.88 ± 0.16, being lower than the controls (1.10 ± 0.09; P = 0.005). CSF PCO₂/PaCO₂ was 0.93 ± 0.13, being higher than the controls (0.84 ± 0.06; P = 0.039). Ipsilateral-to-contralateral CBF ratio had a positive correlation with CSF PO₂/PaO₂ (P = 0.0028) but a negative correlation with the CSF PCO₂/PaCO₂ (P = 0.0045). STA-MCA anastomosis increased CSF pH from 7.402 ± 0.133 to 7.504 ± 0.126 (P = 0.0011) and CSF PO₂/PaO₂ from 0.88 ± 0.16 to 1.05 ± 0.26 (P = 0.018) but decreased CSF PCO₂/PaCO₂ from 0.93 ± 0.13 to 0.70 ± 0.17 (P = 0.0006). Conclusion: The severity of cerebral ischemia before surgery is intensely reflected in the gas tensions and pH of the CSF. STA-MCA anastomosis carries dramatic effects on CSF gas tensions and pH in hemodynamically compromised patients. CSF would be a valuable surrogate biomarker to monitor the severity of cerebral ischemia.