Intra-aortic balloon counterpulsation in newborn lambs infected with group B streptococcus. To determine the efficacy of intra-aortic balloon counterpulsation (IABC) in neonatal group B Streptococcal (GBS) infection, we studied five lambs, 10-14 days old, weighing from 4.7 to 6.7 kg. The lambs were instrumented with arterial and venous catheters, and a 5 French intra-aortic balloon catheter with balloon volumes of 3-5 ml was inserted into the femoral artery. A continuous infusion of heat-killed GBS organisms was infused at a rate of 1.7 to 6.2 x 10(8) org/kg/min, until a 30-50% decrease in cardiac output was attained. IABC was then instituted for 30 minutes, hemodynamic measurements repeated, and IABC was stopped. GBS infusion caused significant decreases in cardiac output (282 +/- 62 vs. 165 +/- 38 ml/min/kg) and pH (7.39 +/- 0.02 vs. 7.33 +/- 0.06), and significant increases in mean pulmonary artery pressure (14.4 +/- 2.1 vs. 36.2 +/- 12.1 mm Hg) and pulmonary vascular resistance (1.20 +/- 0.38 vs. 5.08 +/- 1.49 mm Hg/L/min/kg). Institution of IABC during continuous GBS infusion significantly increased cardiac output (225 +/- 1.27 ml/min/kg). The institution of the IABC also resulted in a significant decrease in pulmonary vascular resistance (2.6 +/- 1.3 mm Hg/L/min/kg). The authors conclude that IABC improves cardiac output and decreases pulmonary vascular resistance in newborn lambs with GBS infection. 