Statistical analysis: At each time-point (baseline, during perfusion, end of sodium lactate infusion), differences of mean MD glucose, lactate, pyruvate, PbtO2, CBF, Mean transit time, ICP, CPP will be analyzed. We will also examine the percentage time spent with abnormal values (MD glucose < 1 mmol/L, PbtO2 < 20 mm Hg, ICP > 20 mm Hg). Differences will be compared using ANOVA for repeated measures.