Metabolic distress is commonly defined as LPR greater than 40, whereas metabolic crisis comprises the combination of LPR greater than 40 and brain glucose less than 0.7 mmol/L.21,79-81 Metabolic distress/crisis, therefore, is a composite value that reflects, in the direct measurement of brain glucose and its anaerobic and aerobic metabolites (lactate/pyruvate), the difference between energy supply and demand.21,81 A reduction in energy supply can be caused by reduced CBF, which decreases the oxygen and glucose supply, resulting in a shift to anaerobic metabolism with increased brain lactate.79 Alternatively, low glucose availability can lead to a decrease in brain pyruvate without an increase in lactate.76,80 Elevated LPR with and without low MD-glucose, high brain-serum glucose variability, high MD-lactate, and high MD-glutamate concentration, measured in the interstitial space by MD, have been linked with poor outcome in patients with acute brain injury (including TBI and SAH patients).70-76,82-84 The etiology of MC is diverse, including low CPP, elevated ICP, spreading depolarizations, and others.83-86