title: [Does Stewart-Fencl improve the evaluation of acid-base status in stable patients on hemodiafiltration?].
abstract: BACKGROUND
  The traditional evaluation of acid-base status relies on the Henderson-Hasselbach equation. In 1983, an alternative approach, based on physical and chemical principles was proposed by P. Stewart. In this approach, plasma pH is determined by 3 independent variables: pCO2, Strong Ion Difference (SIDm), which is the difference between the strong cations (Na +, K +, Ca ++, Mg ++) and the strong anions (Cl-, lactate) and total plasma concentration of nonvolatile weak acids (ATot), mainly inorganic phosphate and albumin. Bicarbonate is considered a dependent variable. The aim of this study was to evaluate the acid-base status using both perspectives, physical chemical and traditional approach.
  
  
  METHODS
  We studied 35 patients (24 M; 11F) on hemodiafiltration, mean age was 67,2+/-15,7, 8+/-19,2 kg. We analyzed plasma chemistry including pH, pCO2, HCO3-, base excess and Na+, K+, Cl-, Ca++, Mg++, lactate and SIDm. The SID estimated (SIDe) was calculated by Figge's formula (1000 x 2.46E-11 x pCO2 / (10-pH) + Album gr/dl x (0.123 x pH-0.631) + P in mmol/l x (0.309 x pH-0.469) and Gap of the SID as the difference SIDm-SIDe.
  
  
  RESULTS
  pH preHD was 7,36+/-0,08 and pH posHD 7,44+/-0,08 (p < 0.001). There was no significant differences between pCO2 pre and pos-HD. HCO3 - and base excess increased during the session (p < 0.001). SIDm decreased from 46,2+/-2,9 preHD to 45+/-2,3 mEq/l postHD (p < 0.05). On the opposite, SIDe increased from 38,5+/-3,8 to 42,9+/-3,1 mEq/l (p < 0.001). The Gap Anion descended from 18,6+/-3,8 preHD to 12,8+/-2,8 mEq/l mEq/l postHD (p < 0.001) and the Gap of the SID 7,6+/-3 to 2,1+/-2 (p < 0.001). Anion Gap correlated with the Gap-SID so much pre-HDF as pos-HDF. Delta Base excess correlated only with Delta of the Gap SID.
  
  
  CONCLUSIONS
  Stewart-Fencl's approach does not improve characterization of acid-base status in patients on chronic HDF. In presence of normocloremia the SIDm does not reflect the alkalinizing process of the session of hemodialysis. According this approach, hemodialysis therapy can be viewed as a withdrawal of inorganic anions, especially the sulphate. These anions are replaced by OH - and secondarily for HCO3-. The approach only improves the evaluation of unmeasured anions by the Gap of the SID, without the effect of albumin and phosphate.
authors.affiliation: Servicio de Nefrología, Hospital General de Castellón, Castellón. hernandez_jul@gva.es
authors.forename: J
authors.initials: J
authors.lastname: Hernández Jaras
authors.forename: I
authors.initials: I
authors.lastname: Rico Salvador
authors.forename: E
authors.initials: E
authors.lastname: Torregrosa de Juan
authors.forename: R
authors.initials: R
authors.lastname: Pons Prades
authors.forename: A
authors.initials: A
authors.lastname: Rius Peris
authors.forename: M A
authors.initials: MA
authors.lastname: Fenollosa Segarra
authors.forename: J J
authors.initials: JJ
authors.lastname: Sánchez Canel
authors.forename: T
authors.initials: T
authors.lastname: Carbajo Mateo
mesh_terms: D000136:Acid-Base Equilibrium; D000137:Acid-Base Imbalance / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control; D000138:Acidosis / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D000838:Anions / Q000097:blood; D001639:Bicarbonates / Q000097:blood; D002245:Carbon Dioxide / Q000097:blood; D002412:Cations / Q000097:blood; D005260:Female; D017583:Hemodiafiltration / Q000009:adverse effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007676:Kidney Failure, Chronic / Q000097:blood / Q000150:complications / Q000628:therapy; D008297:Male; D008875:Middle Aged
chemical_list: D000838:Anions; D001639:Bicarbonates; D002412:Cations; D002245:Carbon Dioxide