Magnetic resonance spectroscopy of anoxic brain injury after cardiac arrest

Objective We describe magnetic resonance spectroscopy (MRS) changes in comatose patients undergoing targeted temperature management (TTM) after cardiac arrest, and their relationships to relevant clinical, MRI, and EEG variables. Methods A prospective cohort of 50 patients was studied. The primary outcome was coma recovery to follow commands. Comparison of MRS measures in the posterior cingulate gyrus, parietal white matter, basal ganglia, and brainstem were also made to 25 normative control subjects. Results Fourteen of 50 achieved coma recovery. Compared to patients who recovered, there was a significant decrease in total N-acetyl-aspartate (NAA/Cr) and glutamate; and an increase in lactate (Lac/Cr) and glutamine in patients who did not recover, with changes most prominent in the posterior cingulate gyrus. Patients who recovered had a decrease in NAA/Cr as compared to control subjects. Coma recovery was seen in patients with a moderate decrease in NAA/Cr, but the appearance of lactate resulted in a poor outcome. NAA/Cr had a linear relationship with MRI cortical apparent diffusion coefficient (ADC); lactate level exponentially increased with decreasing ADC. EEG suppression/burst suppression was universally associated with lactate elevation. Conclusions NAA and lactate changes are associated with clinical/MRI/EEG changes consistent with anoxic brain injury and are most prominent in the posterior cingulate gyrus. NAA/Cr decrease observed in patients with good outcomes suggests mild anoxic injury in patients asymptomatic at hospital discharge. The appearance of cortical lactate represents a deterioration of aerobic energy metabolism and is associated with EEG background suppression, synaptic transmission failure, and severe, potentially irreversible anoxic injury.