Association of cerebral microdialysis monitoring with clinical outcomes after traumatic brain injury; A systematic review.

Objective: Cerebral microdialysis (CMD) enables bedside monitoring of cerebral metabolism after traumatic brain injury (TBI). This systematic review evaluates associations between CMD-derived analytes and mortality and functional outcome in adults with moderate-to-severe TBI. Methods: A systematic review was conducted of adult patients with moderate-to-severe TBI (Glasgow Coma Scale ≤12) undergoing CMD monitoring of glucose, lactate, pyruvate, lactate/pyruvate ratio (LPR), glutamate, and/or glycerol. Prespecified outcomes were mortality and functional outcome (Glasgow Outcome Scale, Glasgow Outcome Scale-Extended or modified Rankin Scale). Due to substantial between-study heterogeneity, findings were synthesized qualitatively. Results: The database search identified 1342 records; 33 studies met inclusion criteria. CMD-glucose and CMD-lactate were the most commonly measure analytes (26 studies each), and the least was CMD-glycerol (12 studies). 9 studies have analyzed as a combined biochemical pattern or multimodal modality in relation to outcome. Higher CMD-glucose levels were mostly associated with better outcomes, whereas lower CMD-glucose and elevated CMD- LPR, CMD-glutamate and CMD-glycerol levels were associated with mortality or unfavorable functional outcome. However, analyte thresholds, probe locations, monitoring windows and outcome definitions varied widely and adjusted prognostic estimates were rarely reported. Certainty of evidence was predominantly low to very low. Conclusion: CMD biomarkers show directional associations with outcome after moderate-to-severe TBI, but the evidence is heterogeneous and of low certainty, insufficient to support routine use of CMD analytes for prognostic stratification. Standardization of analyte thresholds, probe location, monitoring windows is needed before their prognostic value can be established.