Comparison of THAM and sodium bicarbonate in resuscitation of the heart after ventricular fibrillation in dogs.

Tris (hydroxymethyl) aminomethane (tromethamine or THAM) has been suggested as an effective substitute for sodium bicarbonate (NaHCO3) in the treatment of metabolic acidosis accompanying cardiac arrest. Even though several reports on its appraisal have been published, there is still no clear agreement on its therapeutic value. A double-blind study was therefore lndertaken to compare in 36 dogs the effectiveness of 0.6 M THAM, 0.3 M THAM, and NaHCO3 (0.892 mEq/ml) to correct metabolic acidosis produced during 3 minutes of cardiac fibrillation, followed by a 3-minute period of cardiac compression. The dogs were then defibrillated and observed for 45 minutes. One group of 8 dogs was treated with 0.9 percent NaCl infusion. Compared with 0.9 percent NaCl, both THAM and NaHCO3 were equally effective in correcting metabolic acidosis (p less than 0.05). Initially, 0.6 M THAM produced a more pronounced (p less than 0.05) elevation of blood pH, but this effect was not sustained during the later postdefibrillation period. There was little difference in the effect of either of these drugs on mean aortic pressure and total peripheral vascular resistance. It is concluded that adequate ventilation and effective cardiac compression are still the chief criteria on which the final outcome of cardiac resuscitation depends. Correction of metabolic acidosis is important supportive therapy, but either THAM or NaHCO3 can be used with comparatively equivalent effect.