Effects of THAM and sodium bicarbonate on intracranial pressure and mean arterial pressure in an animal model of focal cerebral injury

Episodes of arterial hypotension are associated with an increased mortality in head injury patients. Rapid infusion of sodium bicarbonate in such patients may cause hypotension and elevate intracranial pressure. Therefore, we examined the effects of tromethamine (THAM) versus bicarbonate on intracranial pressure and blood pressure in a model of focal cerebral injury. THAM is a buffer that in previous studies has been shown to lower intracranial pressure. After creation of a cryogenic lesion in 13 New Zealand white rabbits, equivalent infusions (15 s duration) of sodium bicarbonate and THAM (2 mEq/kg) were administered sequentially to each animal in random order. Rapid infusion was chosen to simulate the administration of these drugs during a resuscitation. THAM infusion was associated with a significantly lower intracranial pressure and blood pressure than bicarbonate. The fall in blood pressure was great enough that cerebral perfusion pressure after THAM infusion was significantly lower than after bicarbonate infusion. In this model of cerebral injury, rapid infusion of THAM offered no therapeutic advantage over bicarbonate.