[The Davenport diagram and the international system of units]

The implantation of the international system of units in medical science leads to revising the Davenport diagram. This diagram has been widely used for 20 years as a system displaying the variations in acid-base equilibrium. In order to conserve its familiar aspect the coordinates are: a pH abscissa complete with a scale of H+ ion concentrations (nmol.l-1) and an ordinate using real plasma HCO-3 concentrations. The isobars of PCO2 are reconstructed for whole and semi-whole kilopascal values (kPa). The real plasma buffer lines are reconstructed for 3, 6 and 9 n.mmol.-1 of monomeric hemoglobin which are the nearest whole values of 5, 10 and 15 g of Hb/100 ml. The diagram is calculated for 37 degrees C and the constants used for pK' and aCO2 are the most recently suggested values.