Effect of meconium on the hemoglobin–oxygen association curve

Our purpose was to determine the effect of meconium-stained amniotic fluid on the hemoglobin-oxygen association curve of maternal whole blood. Whole blood was obtained from term gravidas in active labor. Hemoglobin-oxygen association curves were generated for blood incubated with meconium vs. controls. Oxygen association curves were determined at pH 7.4 and 37 degrees C utilizing an automated device consisting of a spectrophotometer cuvette fitted with a magnetic stirrer, gas exchange line, and a Clark oxygen electrode. The samples were deoxygenated with nitrogen and association curves recorded while reoxygenating. Data was analyzed with Sigma Plot and Sigma Stat software. Analysis included log transformation, linear regression, and paired t-test. Twenty-eight hemoglobin oxygen association curves were generated. In all 14 pairs, meconium shifted the hemoglobin-oxygen association curve to the right. Partial pressures of oxygen required for various degrees of hemoglobin saturation were higher in meconium-exposed samples; P50 (30.1+/-0.6 vs. 27.8+/-0.4 mmHg, P < 0.01); P75 (46.9+/-0.6 vs. 43.1+/-0.5 mmHg, P < .001); P90 (69.2+/-1 vs. 63.3+/-1 mmHg, P < 0.01). Meconium-stained amniotic fluid causes a statistically significant, but clinically small, right shift in the hemoglobin-oxygen association curve.