Evaluation of acid–base disorders in dogs and cats presenting to an emergency room. Part 2: Comparison of anion gap, strong ion gap, and semiquantitative analysis

Abstract

Unmeasured anions occurred commonly in this sample of small animal emergency room patients and physiochemical approaches identified more animals with unmeasured anions than the traditional AG calculation. Further studies are needed to determine if the results of the physicochemical approach improves clinical management and warrants the associated increases in cost and complexity.

Evaluation of acid–base disorders in dogs and cats presenting to an emergency room. Part 1: Comparison of three methods of acid–base analysis

“…The semiquantitative parameter, XA identified ummeasured anions in 68/98 of patients, which may reflect a greater diagnostic sensitivity. The assessment of unmeasured anions is further investigated in part 2 of this study published elsewhere in this issue …”

“…The assessment of unmeasured anions is further investigated in part 2 of this study published elsewhere in this issue. 31 The potential clinical benefit of the Stewart and semiquantitative approaches is the ability to determine underlying causes for metabolic acid-base abnormalities that may direct therapy. For instance, an increased SID metabolic alkalosis will likely benefit from the administration of low SID IV fluid such as 0.9% sodium chloride.…”

Determination of reference intervals of acid‐base parameters in clinically healthy dogs

“…The following equations were used to estimate RIs of nontraditional acid‐base parameters: ●Sodium − chloride difference ([Na + ] − [Cl − ]) = [Na + ] − [Cl − ]; ●Chloride/sodium ratio ([Cl − ]/[Na + ] ratio) = [Cl − ]/[Na + ]; ●Chloride gap ([Cl − ] gap) = [Cl − ] mid‐value – ([Cl − ] measured × [Na + ] mid‐value /[Na + ] measured ); ●AGAP = ([Na + ] + [K + ]) − ([HCO 3 − ] + [Cl − ]); ●Anion gap corrected for albumin concentration (AGAP alb ) = AGAP + 4.2 × ([Alb mid‐value ] − [Alb measured ]); ●Anion gap corrected for albumin and phosphorous concentrations (AGAP albp ) = AGAP alb + 1.8 × ([phosphorous mid‐value ] ‐ [phosphorous measured in mmol/L]); ●A tot = ([Alb measured ] × ((0.123 × pH) − 0.631) × 10) + ([phosphorous measured in mmol/L] × ((0.309 × pH) ‐ 0.469)); ●Strong ion difference 1 (SID 1 ) = [Na + ] + [K + ] − [Cl − ]; ●Strong ion difference 2 (SID 2 ) = [Na + ] + [K + ] − [Cl − ] − [lactate − ]; ●Strong ion difference 3 (SID 3 ) = [Na + ] + [K + ] + [Ca 2+ ] − [Cl − ] − [lactate − ]; ●Strong ion difference apparent (SID app ) = [Na + ] + [K + ] + [Ca 2+ ] − [Cl − ]; ●Strong ion difference effective (SID e ) = [A tot + HCO 3 − ]; ●Strong ion gap 1 (SIG 1 ) = ([Alb measured ] × 10 × 0.49) − AGAP; ●Strong ion gap 2 (SIG 2 ) = SID 3 − SID e ; ●Strong ion gap 3 (SIG 3 ) = SID app − SID e ; where electrolytes and lactate were expressed in millimolar per liter and albumin in gram per deciliter. Equations for AGAP and chloride gap were adjusted to mid‐values of the laboratory: sodium 147.5 mmol/L (147.5 mEq/L), chloride 110 mmol/L (110 mEq/L), phosphorous 1.55 mmol/L (4.8 mg/dL) and albumin 2.95 g/dL (29.5 g/L).…”

“…In an effort to improve upon the traditional evaluation of the determinants of pH, Stewart and Fencl proposed a physicochemical approach to acid‐base evaluation that requires evaluation of the contributions of strong ions and weak acids . This method, commonly referred to as the “strong ion approach,” is useful because it reveals more details about the contributors to acid‐base balance and may help identify causes of acid‐base disturbances not identified with the traditional Henderson–Hasselbalch method . According to Stewart's model, pH is determined by 3 independent variables: PCO 2 , which represents the respiratory contribution; the strong ion difference (SID), which represents the contribution of highly dissociated cations and anions; and total plasma nonvolatile weak buffers ( A tot ), which represent the weak anion contribution of albumin, phosphate, and minor organic ions such as uric acid.…”

Listening to the body's response—A dedication to the teachings of Dr. Steve C. Haskins

“…Acid‐base physiology exemplifies this principle and is the subject of 3 studies featured in this special issue. In a 2‐part study, Hopper et al, who were taught and mentored by Dr. Haskins, explore the diagnostic performance of evaluating blood gas and physiological parameters via the traditional approach compared with Stewart's approach and a semi‐quantitative approach. Their findings support something Dr. Haskins clearly believed, which is that the body can adapt and cope with various insults, but that you need to look closely to appreciate these responses.…”