title: Crystalloid strong ion difference determines metabolic acid-base change during in vitro hemodilution.
abstract: OBJECTIVE
  To determine the relationship between the strong ion difference (SID) of a diluting crystalloid and its metabolic acid-base effects on in vitro blood dilution.
  
  
  METHODS
  Prospective in vitro study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Normal human blood.
  
  
  METHODS
  Three solutions were prepared, each with [Na] 140 mmol/L. [Cl-] for solutions 1, 2, and 3 was 120, 110, and 100 mmol/L, respectively, the other anion being HCO3-. SID values were thus 20, 30, and 40 mEq/L, respectively. Serial dilutions of well-oxygenated fresh venous blood were performed anaerobically by using each of solutions 1-3 as well as 0.9% saline (SID = 0 mEq/L) and Hartmann's solution (SID = -4 mEq/L).
  
  
  RESULTS
  Blood gas and electrolyte analyses were performed before and after each dilution. Apart from dilutions with solution 3 (crystalloid SID 40 mEq/L) during which plasma SID did not change, plasma SID decreased during hemodilution. In contrast, base excess increased during hemodilution with solutions 3 and 2 (crystalloid SID 40 mEq/L and 30 mEq/L, respectively) and decreased only with the remaining three solutions. The relationships between hemoglobin concentrations and both plasma SID and whole blood base excess throughout dilution were linear, with slopes proportional to the SID of the diluent in each case. Linear regression revealed that the SID of crystalloid producing a zero base excess/hemoglobin concentration slope during blood dilution (i.e., no change in metabolic acid-base status) is 23.7 mEq/L.
  
  
  CONCLUSIONS
  On in vitro hemodilution, there is a simple linear relationship between diluent crystalloid SID and the rate and direction of change of plasma SID and whole blood base excess. Direct extrapolation to in vivo situations such as acute normovolemic hemodilution and large volume correction of extracellular fluid deficits requires experimental confirmation.
authors.affiliation: Division of Anesthesiology and Intensive Care, Royal Brisbane Hospital, Queensland, Australia.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Morgan
authors.forename: Balasubramanian
authors.initials: B
authors.lastname: Venkatesh
authors.forename: Jonathan
authors.initials: J
authors.lastname: Hall
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects*; D001784:Blood Gas Analysis; D000077324:Crystalloid Solutions; D006438:Hemodilution; D006801:Humans; D066298:In Vitro Techniques; D007477:Ions; D007552:Isotonic Solutions; D010952:Plasma Substitutes / Q000494:pharmacology*
chemical_list: D000077324:Crystalloid Solutions; D007477:Ions; D007552:Isotonic Solutions; D010952:Plasma Substitutes