Effects of buffer agents on postresuscitation myocardial dysfunction.

Abstract

OBJECTIVES: Earlier studies demonstrated that hypertonic buffer agents administered during cardiopulmonary resuscitation (CPR) altered neither myocardial pH nor cardiac resuscitability. The rationale for the routine use of buffer agents for CPR has therefore been challenged. However, when these buffer agents are administered during CPR, they may have favorable effects on the postresuscitation course. Postresuscitation myocardial dysfunction has more recently emerged as a potentially fatal complication after successful cardiac resuscitation. Options for prevention and management of this complication have prompted the present studies, in which the effects of buffer agents administered during CPR are evaluated as to their effects on postresuscitation myocardial function and survival. DESIGN: Prospective, randomized, controlled animal study. SETTING: University animal laboratory. SUBJECTS: Forty male Sprague-Dawley rats (450 to 570 g). INTERVENTIONS: Ventricular fibrillation was induced electrically. Mechanical Ventilation and percordial compression were initiated after either a 4- or an 8-min interval of untreated cardiac arrest. Sodium bicarbonate as a CO2-generating buffer, Carbicarb and tromethamine as CO2-consuming buffers, or hypertonic saline placebo were injected as a bolus into the right atrium during CPR. Defibrillation after 10 mins of cardiac arrest and CPR was successful in each instance. No differences in the electric power required for successful resuscitation were documented. Left ventricular pressure, rate of left ventricular pressure increase measured at a left ventricular pressure of 40 mm Hg (dP/dt40), rate of left ventricular pressure decline (-dP/dt), and end-tidal PCO2 were continuously measured for 240 mins after successful resuscitation. MEASUREMENTS AND MAIN RESULTS: Decreases in coronary perfusion pressure were observed after each buffer or placebo injection. As anticipated, end-tidal PCO2 increased after bicarbonate and decreased after Carbicarb or tromethamine. Postresuscitation left ventricular function was significantly decreased in all animals. However, there was significantly less depression in rate of left ventricular pressure increase measured at a left ventricular pressure of 40 mm Hg (dP/dt40), rate of left ventricular pressure decline (-dP/dt), and a lower left ventricular diastolic pressure with both Carbicarb and tromethamine in association with significant increases in postresuscitation survival rate. When the duration of untreated cardiac arrest was increased to 8 mins, the severity of postresuscitation left ventricular dysfunction was magnified and postresuscitation myocardial function and survival were significantly improved with both CO2-generating and CO2-consuming buffer agents. CONCLUSION: Although buffer agents may not improve the success of resuscitation when administered during CPR, they may ameliorate postresuscitation myocardial dysfunction and thereby improve postresuscitation survival.