Clinical Assessment of Acid‐Base Status: Comparison of the Henderson‐Hasselbalch and Strong Ion Approaches

Abstract

The traditional approach for clinically assessing acid-base status uses the Henderson-Hasselbalch equation to categorize 4 primary acid-base disturbances: respiratory acidosis (increased PCO2), respiratory alkalosis (decreased PCO2), metabolic acidosis (decreased extracellular base excess or actual HCO3- concentration), and metabolic alkalosis (increased extracellular base excess or actual HCO3- concentration). The anion gap is calculated to detect unidentified anions in plasma. This approach works well clinically and is recommended for use whenever serum total protein, albumin, and phosphate concentrations are approximately normal. However, because the Henderson-Hasselbalch approach is more descriptive than mechanistic, when these concentrations are markedly abnormal the Henderson-Hasselbalch equation frequently provides erroneous information as to the cause of an acid-base disturbance. The new quantitive physicochemical approach to evaluating acid-base balance uses the simplified strong ion model to categorize 6 primary acid-base disturbances: respiratory acidosis (increased PCO2), respiratory alkalosis (decreased PCO2), strong ion acidosis (decreased strong ion difference), strong ion alkalosis (increased strong ion difference), nonvolatile buffer ion acidosis (increased plasma concentrations of albumin, globulins, or phosphate), and nonvolatile buffer ion alkalosis (decreased plasma concentrations of albumin, globulins, or phosphate). The strong ion gap is calculated to detect unidentified anions in plasma. The simplified strong ion approach works well clinically and is recommended for use whenever serum total protein, albumin, or phosphate concentrations are markedly abnormal. The simplified strong ion approach is mechanistic and is therefore well suited for describing the cause of any acid-base disturbance.

The use of elements of the Stewart model (Strong Ion Approach) for the diagnostics of respiratory acidosis on the basis of the calculation of a value of a modified anion gap (AGm) in brachycephalic dogs

“…The authors of this paper also wanted to take part in the ongoing discussion on which method that describes the ABB disorders describes them in the most complete way (Russel et al 1996, Constable 2000, McCullough and Constable 2003, Constable and Stampfli 2005, Siegling-Vlitakis et al 2007, Sławuta and Glińska-Suchocka 2012 and, what is important, which one can be applied in everyday veterinary practice. From the clinical point of view, the answer to these questions is not simple.…”

“…The value of pH in the dogs examined, which was lower before the procedure but still within the normal range, an increase in pCO 2 , and concentration of HCO 3 -at the upper limit of a standard (Di Bartola 2006a) prove an occurrence of a compensated respiratory acidosis (Kellum 2000, Di Bartola 2006a, Sławuta et al 2010). In the case of a respiratory acidosis, an organism, which aims at the pH normalization, stimulates kidneys to regenerate HCO 3 -, which increases concentration of these ions in the blood serum (De Morais and Di Bartola 1991, Constable 2000, Morris and Low 2008. In people with the chronic respiratory acidosis, an increase in pCO 2 by each 1 mmHg is accompanied by an increase in HCO 3 -concentration by 0.51 mmol/l (Martinu et al 2003), which, as it results from the research conducted by Alfaro et al (1996), is sufficient for normalization of the blood pH in the course of the disorder.…”

Physicochemical Approach to Determine the Mechanism for Acid–Base Disorders in 793 Hospitalized Foals

“…As shown in this study, 32% of hospitalized foals are hypoproteinemic; this might result in a decreased AG that considerably underestimates the presence of unmeasured anions 47. Unlike the AG, SIG treats total plasma protein and phosphate concentrations as variables and is not affected by changes in pCO 2 or pH 17, 28, 44. In critically ill foals and calves, SIG correlated moderately with [ l ‐lac − ] and was highly correlated with AG,1, 26 whereas Constable et al 28.…”

“…Neither the base excess nor the bicarbonate can explain the cause of a disturbance, only its existence and severity 16, 17. The quantitative physicochemical approach emphasizes the importance of strong ion difference (SID) which is the difference between the charge of plasma strong cations (Na + , K + ,Ca 2+ , Mg 2+ and anions (Cl − , l ‐lactate − , sulfate, and ketoacids), p a CO 2 , and total plasma protein concentration ( A tot ) in determining plasma pH and [${\text{HCO}}_3^{-}$] 18, 19.…”

Acid-base disorders in calves with chronic diarrhea

“…The classic model is based on changes in plasma bicarbonate concentration (HCO 3 -), anion gap and base excess. In general terms, decreased bicarbonate concentration is considered a marker of acidosis, and elevated values of this parameter correspond to alkalosis (Constable 2000). The Stewart model is based on three independent determinants of acid-base balance: pCO 2 , strong ion difference (SID) and total nonvolatile weak acid concentration.…”