Figge J. Role of Non-Volatile Weak Acids (Albumin, Phosphate and Citrate). In Stewart's
Textbook of Acid-Base. Kellum JA and Elbers PWG, editors. Amsterdam: AcidBase.org. 2009.
Chapter 11, pages 217 - 232.
Graphic results of a computer simulation for plasma-like solutions containing albumin as the sole
protein moiety. The simulation is designed to resemble a classic “Davenport diagram” . The
graph demonstrates the covariation of pH and [HCO3- ] as the PCO2
is titrated from 15 to 100 mmHG at two values of [SID] (38.9 and 28.9 mEq / L). The curve for
[SID] = 38.9 mEq / L (upper curve) closely resembles the buffer curve of normal separated human
plasma . The situation with [SID] = 28.9 (lower curve) resembles separated plasma with a
simulated metabolic acidosis. In the case of the lower curve, base excess,
BE = Δ[SID] = 28.9 – 38.9 = -10 (i.e., there is a base
deficit of 10 mmol / L, using Davenport’s nomenclature). Per Davenport, the base deficit can be
estimated directly from the graph as the distance between the two buffer curves along the vertical
line at pH = 7.4: 24.5 – 14.5 = 10 mmol / L base deficit (or -10 mmol / L base excess). The
relationship BE = Δ[SID] holds in this simulation
because the concentrations of non-bicarbonate
buffers, albumin, Pi,TOT and citrateTOT are all held constant. Note that
the isobar at PCO2 = 40
is included for reference. This isobar intersects the upper curve ([SID] = 38.9) at pH = 7.40.