Total weak acid concentration and effective dissociation constant of nonvolatile buffers in human plasma.
Constable, Peter D.
Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, Illinois 61802
APStracts 8:0331A, 2001.
The strong ion approach provides a quantitative physicochemical method for describing the mechanism for an acid-base disturbance. The approach requires species-specific values for the total concentration of plasma nonvolatile buffers (Atot) and the effective dissociation constant for plasma nonvolatile buffers (Ka), but these values have not been determined for human plasma. Accordingly, the purpose of this study was to calculate accurate Atot and Ka values using data obtained from in vitro strong ion titration and CO2 tonometry. The calculated values for Atot (24.1 mmol/l) and Ka (1.05 × 10"minus"7) were significantly (P < 0.05) different from the experimentally determined values for horse plasma and differed from the empirically assumed values for human plasma (Atot = 19.0 meq/l and Ka = 3.0 × 10"minus"7). The derivatives of pH with respect to the three independent variables [strong ion difference (SID), "pco2", and Atot] of the strong ion approach were calculated as follows: dpH/dSID+ = [1 + 10{?(pKa|"minus"|pH)}]2/2.303"lbrace"S"pco2"10(pH|"minus"|pK{1?'})[1 + 10{?(pKa|"minus"|pH)}]2 + Atot10{?(pKa|"minus"|pH)}"rbrace", dpH/d"pco2" = S10"minus"pK{1?'}/"lbrace"2.303[Atot10pH(10pH + 10{?pKa})"minus"2 "minus" SID+10"minus"pH]"rbrace", and dpH/dAtot = "minus"1/"lbrace"2.303[S"pco2"10(pH|"minus"|pK{1?'}) + SID+10{?(pKa|"minus"|pH)}]"rbrace", where S is solubility of CO2 in plasma. The derivatives provide a useful method for calculating the effect of independent changes in SID+, "pco2", and Atot on plasma pH. The calculated values for Atot and Ka should facilitate application of the strong ion approach to acid-base disturbances in humans.
Received 9 January 2001; accepted in final form 12 April 2001
APS Manuscript Number A23-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001