• Michalis Agrafiotis, Maria Sileli, Fotini Ampatzidou, Ilias Keklikoglou, and Panagiotis Panousis.
• From the Second Department of Intensive Care Medicine, 'Georgios Papanikolaou' General Hospital of Thessaloniki, Thessaloniki, Greece.
• Eur J Anaesthesiol. 2013 Nov 1;30(11):678-84.

BackgroundThe 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.ObjectiveTo 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.DesignA retrospective observational study.SettingAdult ICU in a tertiary hospital.PatientsOne hundred and thirty-five cardiac surgical patients admitted for postoperative care.InterventionsNone.Main Outcome MeasuresBE(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.ResultsThe 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).ConclusionThe 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.

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