Traumatic Brain Tissue Acidosis: Experimental and Clinical Studies
We have been focusing on potential metabolic derangement associated with severe head injury and a clinical trial directed toward treating brain tissue acidosis is currently underway. More specifically, we based this study on the hypothesis that following brain trauma brain tissue acidosis develops which may contribute to the prolongation of coma and neurologic deficit. Tromethamine (THAM), a safe and low toxicity agent which buffers in major part by causing a hypocapnic alkalosis, was selected for trial. Patients admitted with GCS < 8 were randomized into one of three arms: control; THAM plus hyperventilation; hyperventilation alone. Each regimen was maintained for 5 days post injury. Our analysis of 3 and 6 months Glasgow outcome score showed that prophylactic hyperventilation retards recovery, and the use of THAM overcomes the apparent deleterious effects of hyperventilation. One explanation is that the reduced ICP instability observed in THAM treated patients may account for this improvement. Is THAM effective in buffering traumatized brain tissue? What factors account for improvement in ICP stability?
We addressed these questions in experimental studies utilizing MR spectroscopy to measure brain lactate production and tissue pH in fluid percussed anaesthetized cats. The protocol was designed to match our clinical trial, and brain injured animals were randomized into control, THAM, and hyperventilated groups. We observed that brain lactate production increased with trauma and remained above control at 8 hrs post injury. Lactate production in THAM treated animals was not elevated. Highest lactate production was associated with injured animals treated with sustained hyperventilation. We also observed that the PCr/Pi ratio in trauma alone was reduced to 78% of control at 1 hr and to 65% in the hyperventilated group. The reduction of PCr/Pi of the THAM treated group was similar to the reduction seen in trauma alone and equaled 77.8%. Brain tissue pH of THAM treated animals was slightly alkalotic compared to trauma controls.
These data suggest that THAM treatment moderates the pH disturbances following trauma and the slightly alkalotic milieu may improve ICP stability in patients by helping to maintain vasoconstriction.
KeywordsHead injury brain tissue acidosis lactate production THAM buffering
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