title: A head to head evaluation of 8 biochemical scanning tools for unmeasured ions.
abstract: We aimed to evaluate the sensitivity and specificity of 8 biochemical scanning tools in signalling the presence of unmeasured anions. We used blood gas and biochemical data from 15 patients during and after cardio-pulmonary bypass. Sampling time-points were pre-bypass (T1), 2 min post equilibration with priming fluid containing acetate and gluconate anions (T2), late bypass (T3) and 4 h after surgery (T4). We calculated the anion gap (AG), albumin-corrected anion gap (AGc), whole blood base excess (BE) gap, plasma BE gap, standard BE gap and the strong ion gap (SIG), plus 2 new indices-the unmeasured ion index (UIX) and unmeasured plasma anions according to the interstitial, plasma and erythrocyte acid-base model (IPEua). Total measured plasma concentrations of acetate and gluconate [XA] were proxies for unmeasured plasma anions. [XA] values (mmol/L) were 1.41 (0.87) at T1, 11.73 (3.28) at T2, 4.80 (1.49) at T3 and 1.36 (0.73) at T4. Corresponding [albumin] values (g/L) were 32.3 (2.0), 19.8 (2.6), 21.3 (2.5) and 29.1 (2.3) respectively. Only the AG failed to increase significantly at T2 in response to a mean [XA] surge of >10 mEq/L. At an [XA] threshold of 6 mEq/L, areas under receiver -operator characteristic curves in rank order were IPEua and UIX (0.88 and 0.87 respectively), SIG (0.81), AGc (0.79), standard BE gap (0.77), plasma BE gap (0.71), BE gap (0.70) and AG (0.59). Similar ranking hierarchies applied to positive and negative predictive values. We conclude that during acute hemodilution UIX and IPEua are superior to the anion gap (with and without albumin correction) and 4 other indices as scanning tools for unmeasured anions.
authors.affiliation: Intensive Care Unit, Mater Research, Mater Health Services, University of Queensland, Salmon Building, Raymond Terrace, South Brisbane, QLD, 4101, Australia. t.morgan@uq.edu.au.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Morgan
authors.affiliation: Department of Intensive Care, Sunshine Coast Hospital, Nambour, QLD, 4560, Australia.|University of Queensland, Brisbane, QLD, 4101, Australia.
authors.forename: Chris M
authors.initials: CM
authors.lastname: Anstey
authors.affiliation: Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, SC, 29209, USA.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Wolf
mesh_terms: D000085:Acetates / Q000097:blood; D000136:Acid-Base Equilibrium; D000137:Acid-Base Imbalance / Q000097:blood*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000418:Albumins / Q000032:analysis; D019540:Area Under Curve; D001639:Bicarbonates / Q000008:administration & dosage; D001784:Blood Gas Analysis / Q000295:instrumentation* / Q000379:methods*; D002315:Cardiopulmonary Bypass / Q000379:methods; D002712:Chlorides / Q000008:administration & dosage; D005260:Female; D005942:Gluconates / Q000097:blood; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000097:blood*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D009243:NAD / Q000097:blood; D009249:NADP / Q000097:blood; D012372:ROC Curve; D012680:Sensitivity and Specificity; D012964:Sodium / Q000008:administration & dosage; D013997:Time Factors; D055815:Young Adult
chemical_list: D000085:Acetates; D000418:Albumins; D001639:Bicarbonates; D002712:Chlorides; D005942:Gluconates; D007477:Ions; D009243:NAD; D009249:NADP; D012964:Sodium; C030691:gluconic acid
keywords: Biochemical scanning tools; Cardio-pulmonary bypass; IPE model; UIX; Unmeasured anions