title: The base excess gap is not a valid tool for the quantification of unmeasured ions in cardiac surgical patients: a retrospective observational study.
abstract: BACKGROUND
  The base excess gap (BE(gap)) method is commonly used for the quantification of unmeasured ions in critically ill patients. However, it has never been validated against the standard quantitative acid-base approach.
  
  
  OBJECTIVE
  To compare the BE(gap) as a tool for the prediction of the excess of unmeasured ions with the offset of strong ion gap (SIG) from its reference value.
  
  
  METHODS
  A retrospective observational study.
  
  
  METHODS
  Adult ICU in a tertiary hospital.
  
  
  METHODS
  One hundred and thirty-five cardiac surgical patients admitted for postoperative care.
  
  
  METHODS
  None.
  
  
  METHODS
  BE(gap) was calculated as BE(gap) = SBE - BE(si) - BE(wa), where SBE is the standard base excess, BE(si) is the partition due to strong ions ([Na+]-[Cl-]-[lactate-] - 30.5) and BE(wa) is the partition due to weak acids [0.25×{42 - (albumin)}]. The deviation of the observed SIG (SIG(ob)) from its reference value was calculated as deltaSIG = 2.85 - SIG(ob). We used Bland-Altman and concordance correlation analysis to compare BE(gap) with deltaSIG. A bias of ±1 meq l(-1) with limits of agreement of ±2 meq l(-1) and a concordant correlation coefficient of more than 0.9 were considered to indicate a strong agreement.
  
  
  RESULTS
  The concordant correlation coefficient between BE(gap) and deltaSIG was 0.702. The mean bias between the two variables was 1.8 meq l(-1), with a lower limit of agreement of -0.9 meq l(-1) and an upper limit of agreement of 4.4 meq l(-1).
  
  
  CONCLUSIONS
  The BE gap method cannot reliably quantify the unmeasured ion excess in cardiac surgical patients. Clinicians should use the full Stewart-Figge model for quantitative acid-base assessments.
authors.affiliation: From the Second Department of Intensive Care Medicine, 'Georgios Papanikolaou' General Hospital of Thessaloniki, Thessaloniki, Greece.
authors.forename: Michalis
authors.initials: M
authors.lastname: Agrafiotis
authors.forename: Maria
authors.initials: M
authors.lastname: Sileli
authors.forename: Fotini
authors.initials: F
authors.lastname: Ampatzidou
authors.forename: Ilias
authors.initials: I
authors.lastname: Keklikoglou
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Panousis
mesh_terms: D000136:Acid-Base Equilibrium; D000137:Acid-Base Imbalance / Q000097:blood*; D000368:Aged; D002245:Carbon Dioxide / Q000737:chemistry; D006348:Cardiac Surgical Procedures / Q000379:methods*; D016638:Critical Illness; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D007477:Ions / Q000032:analysis*; D019344:Lactic Acid / Q000737:chemistry; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015203:Reproducibility of Results; D012189:Retrospective Studies; D062606:Tertiary Care Centers
chemical_list: D007477:Ions; D002245:Carbon Dioxide; D019344:Lactic Acid