There is controversy regarding the use of
alkalinizing agents during reperfusion after
cardiac arrest. The potential deleterious effects of
sodium bicarbonate (bicarb) administration, including paradoxic cerebral
acidosis, have led to the search for alternative agents.
Tromethamine (tris) is a non-CO2-generating
buffer that has been proposed for use during
cardiopulmonary resuscitation. The purpose of this experiment was to compare the ability of tris with bicarb to correct brain pH (pH B) during reperfusion after a 12-minute
cardiac arrest. Adult mongrel dogs were instrumented and placed in the bore of a Bruker Biospec 1.89 tesla superconducting magnet system.
Ventricular fibrillation was induced; after 12 minutes,
cardiopulmonary bypass was initiated and maintained for two hours with minimum flows of 80 mL/kg/min. Bicarb (n = 5) or tris (n = 5) were administered to correct arterial pH as rapidly as possible. 31P NMR spectra were obtained at baseline and throughout
ischemia and reperfusion. The pH B was determined with the
inorganic phosphate relative to the
phosphocreatine resonance signal shift. Profile analysis indicates a difference between groups (P less than .02) related to an initial delay in pH B correction in the tris group. By 48 minutes of reperfusion, pH B did not differ between the groups. Moreover, there was no evidence of paradoxic cerebral
acidosis in the bicarb group. Although tris corrects blood pH as quickly as bicarb, it is less effective in correcting pH B. Absence of paradoxic
acidosis may be caused by efficient elimination of CO2 by
cardiopulmonary bypass.