Application Of Rapid-Sampling, Online Microdialysis To The Monitoring Of Brain Metabolism During Aneurysm Surgery

OBJECTIVE: To introduce rapid-sampling microdialysis for the early detection of adverse metabolic changes in tissue at risk during aneurysm surgery. METHODS: A microdialysis catheter was inserted under direct vision into at-risk cortex at the start of surgery. This monitoring was sustained throughout the course of the operation, during which intraoperative events, for example, temporary arterial occlusion or lobe retraction, were precisely documented. A continuous online flow of dialysate was fed into a mobile bedside glucose and lactate analyser. This comprises flow-injection dual-assay enzyme-based biosensors capable of determining values of metabolites every 30 seconds. RESULTS: Eight patients underwent clipping or wrapping of intracranial aneurysms and were monitored. Time between events and detection: 9 minutes. Mean change in metabolite value ± standard deviation: temporal lobe retraction lactate, +656 ± 562 μmol/L (n = 7, P< 0.05); glucose, -123 ± 138 μmol/L (n = 6, P = 0.08). Glucose intravenous bolus infusion glucose, +512 ± 244 μmol/L (n = 5, P < 0.01); peak at mean time after bolus, 16 minutes. Temporary proximal clip lactate, +731 ± 346 μmol/L (n = 6, P < 0.01); glucose, -139 ± 96 μmol/L (n = 5, P < 0.05); mean clip time, 8.6 minutes. CONCLUSION: The technique detects changes 9 minutes after intraoperative events occur (limited only by probe-to-sensor tubing length and dialysate flow rate). This provides reliable information to the surgeon and anesthetist promptly. It is a useful method for monitoring glucose and lactate in dialysate, particularly when rapid, transient changes in brain analyte levels need to be determined and the alternative offline methodology would be inadequate.