Bicarbonate Does Not Increase Left Ventricular Contractility During L-Lactic Acidemia in Pigs

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Abstract
Lactic acidosis decreases left ventricular contractility, but whether bicarbonate increases left ventricular contractility during lactic acidosis in vivo is controversial. Therefore, we measured hemodynamics and left ventricular mechanics before and after bicarbonate administration during L-lactic acid infusion in 15 anesthetized pigs. The pigs were beta-blocked and atrially paced to minimize indirect effects of acidosis on contractility. We measured mean arterial pressure, left ventricular end-diastolic pressure, thermodilution cardiac output, left ventricular pressure (Miller catheter), and left ventricular volume (three orthogonal pairs of ultrasonic crystals). Left ventricular contractility was assessed primarily using the slope (Emax) of the end-systolic pressure-volume relationship. While PCO2 was kept constant, 0.2 M L-lactic acid was infused, which reduced arterial pH to 7.05 +/- 0.06. Animals were then randomized to receive either 1 M NaHCO3 (n = 8), which increased pH to 7.45 +/- 0.11, or an equivalent amount of 1 M NaCl (n = 7). Bicarbonate decreased mean arterial pressure (105 +/- 20 to 95 +/- 39 mm Hg, p < 0.05) but did not increase cardiac output. These effects were not significantly different from the effects of saline. Bicarbonate did not significantly increase Emax (4.2 +/- 0.8 to 4.9 +/- 0.8 mm Hg/ml) and was indistinguishable from saline (5.0 +/- 0.7 to 5.2 +/- 0.7 mm Hg/ml). We conclude that bicarbonate infusion does not directly increase left ventricular contractility during lactic acidemia in pigs within this pH range.