Abstract
Extract: Changes in the acid-base status of blood in vivo have been investigated in anesthetized, nephrectomized, artificially ventilated dogs during acute hypercapnia before and after induced changes in body composition. The experiments were designed to study factors influencing the redistribution of bicarbonate generated by buffers in the blood compartments and the interstitial fluid volume.
The first series of experiments was designed to determine the best linear fit to data collected in vivo in dogs with acute steady state hypercapnia (the so-called in vivo CO2 equilibration curve). Three groups were studied: a control group, a group with expanded extracellular fluid (ECF), and a group with expanded blood volume. A linear relation was found between pH-log Pco2 and [H+]-Pco2, the correlation coefficients being 0.98 for both pairs of variables in all three groups. The pH-log Pco2 coordinate system was adopted. The linear relation between pH and log Pco2 allows the slope (Δlog Pco2 ΔpH) of the in vivo CO2 equilibration curve to be determined by measuring only two points on the line.
In the second series of experiments, the slope of the in vivo CO2 equilibration curve was determined before and after body composition was altered so that each dog served as his own control. Six groups of dogs were studied: group 1 (six dogs) was control and had no change in body composition; groups 2 and 3 (six dogs each), ECF volume was increased by infusing 100 and 200 ml/kg, respectively, of a mock ECF solution; group 4 (eight dogs), blood volume was increased by infusing 50 ml/kg fresh, heparinized whole blood; group 5 (eight dogs), hemoglobin concentration was decreased by replacing blood with plasma; and group 6 (four dogs), hemoglobin concentration was increased by infusing 25–30 ml/kg packed erythrocytes. Statistical analysis of the changes in slopes caused by these changes in body composition (Table V) showed the following results: slope increased significantly as plasma bicarbonate concentration fell; slope decreased significantly as ECF volume increased; slope increased significantly as blood volume increased; slope did not change significantly with acute changes in hemoglobin concentration.
Speculation: This study indicates that the slope of the in vivo CO2 equilibration curve is dependent upon certain variables of body composition, especially the volume of the extracellular fluid (ECF) and blood. Thus, correct interpretation of blood acid-base data in acute hypercapnia must take account of the redistribution of bicarbonate as a function of the body composition. For example, an infant born prematurely presenting.
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Deli, R., Lee, C. & Winters, R. Influence of Body Composition on the In Vivo Response to Acute Hypercapnia. Pediatr Res 5, 523–538 (1971). https://doi.org/10.1203/00006450-197110000-00005
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DOI: https://doi.org/10.1203/00006450-197110000-00005