['Elevated brain potassium levels ([K+]) are associated with neuronal damage in experimental models. The role of brain extracellular [K+] in patients with poor-grade aneurysmal subarachnoid hemorrhage (aSAH) and its association with hemorrhage load, metabolic dysfunction and outcome has not been studied so far.', 'Cerebral microdialysis (CMD) samples from 28 poor grade aSAH patients were analyzed for CMD [K+] for 12 consecutive days after ictus, and time-matched to brain metabolic and hemodynamic parameters as well as corresponding plasma [K+]. Statistical analysis was performed using a generalized estimating equation with an autoregressive function to handle repeated observations of an individual patient.', "CMD [K+] did not correlate with plasma [K+] (Spearman's ρ = 0.114, P = 0.109). Higher CMD [K+] was associated with the presence of intracerebral hematoma on admission head computed tomography, CMD lactate/pyruvate ratio >40 and CMD lactate >4 mmol/L (P < 0.05). In vitro retrodialysis data suggest that high CMD [K+] was of brain cellular origin. Higher CMD [K+] was significantly associated with poor 3-month outcome, even after adjusting for age and disease severity (P < 0.01)."] Is higher brain extracellular potassium associated with brain metabolic distress and poor outcome after aneurysmal subarachnoid hemorrhage?