Comparison of sodium bicarbonate, Carbicarb, and THAM during cardiopulmonary resuscitation in dogs

Objectives: During cardiopulmonary resuscitation (CPR), elimination of CO 2 was shown to be limited by low tissue perfusion, especially when very low perfusion pressures were generated. It has therefore been suggested that sodium bicarbonate (NaHCO 3 ), by producing CO 2 , might aggravate the hypercarbic component of the existing acidosis and thereby worsen CPR outcome. The objectives of this study were to evaluate the effects of CO 2 producing and non-CO 2 producing buffers in a canine model of prolonged ventricular fibrillation followed by effective CPR. Design: Prospective, randomized, controlled, blinded trial. Setting: Experimental animal research laboratory in a university research center. Subjects: Thirty-eight adult dogs, weighing 20 to 35 kg. Interventions: Animals were prepared for study with thiopental followed by halothane, diazepam, and pancuronium. Ventricular fibrillation was electrically induced, and after 10 mins, CPR was initiated, including ventilation with an FIO 2 of 1.0, manual chest compressions, administration of epinephrine (0.1 mglkg every 5 mins), and defibrillation. A dose of buffer, equivalent to 1 mmol/kg of NaHCO 3 , was administered every 10 mins from start of CPR. Animals were randomized to receive either NaHCO 3 , Carbicarb, THAM, or 0.9% sodium chloride (NaCI). CPR was continued for up to 40 mins or until return of spontaneous circulation. Measurements and Main Results: Buffer-treated animals had a higher resuscitability rate compared with NaCI controls. Spontaneous circulation returned earlier and at a significantly higher rate after NaHCO 3 ,(in seven of nine dogs), and after Carbicarb (six of ten dogs) compared with NaCI controls (two of ten dogs). Spontaneous circulation was achieved twice as fast after NaHCO 3 compared with NaCI (14.6 vs. 28 mins, respectively). Hydrogen ion (H + ) concentration and base excess, obtained 2 mins after the first buffer dose, were the best predictors of resuscitability. Arterial and mixed venous PCO 2 did not increase after NaHCO 3 or Carbicarb compared with NaCI. Conclusions: Buffer therapy promotes successful resuscitation after prolonged cardiac arrest, regardless of coronary perfusion pressure. NaHCO 3 , and to a lesser degree, Carbicarb, are beneficial in promoting early return of spontaneous circulation. When epinephrine is used to promote tissue perfusion, there is no evidence for hypercarbic venous acidosis associated with the use of these CO 2 generating buffers.