Effect of natural variations in PaCO2 on plasma [HCO3-] in dogs: a redefinition of normal

Abstract

Graded degrees of both chronic hyper- and hypocapnia are known to induce renal responses that significantly alter plasma bicarbonate concentration. These findings have raised the possibility that even normal variations in PaCO2 play an important role in determining the exact level of bicarbonate in plasma. To test this hypothesis, we examined the relationship between resting levels of PaCO2 and the plasma bicarbonate concentration in two groups of normal dogs, one ingesting a normal salt diet and the other a salt-restricted diet. The results indicate that values for bicarbonate within the normal range are highly dependent on the prevaling level of carbon dioxide tension ([HCO3-] = 0.35 PaCO2 + 9.0, r = 0.72). Accordingly, approximately 50% of the normal variance in bicarbonate concentration is explained simply by the variance in PaCO2. The joint confidence region for bicarbonate concentration and PaCO2, which can be derived from these data, provides a new and more rigorous definition of the normal range for acid-base values in the dog.

Plasma Bicarbonate and CO₂ Tension

“…Again using the extremes calculated from Madias's data, we took eleven total C 0 2 values between 25.0 and 28. [3] were nearly the same as the ones they calculated from their data in humans [2].…”

“…The relation between plasma bicarbonate concentration ( [HCOf]) and CO, tension (Pco,)was studied by Madias et al in normal humans [2] and in dogs [3], They measured total plasma C 0 2 content and blood pH, from which they then calculated [HC03'] and Pco,. We wondered whether the relation they found between the latter two variables might be mainly inherent in the HendersonHasselbalch equation.…”

Experimental Determination of Net Protein Charge andAtotandKaof Nonvolatile Buffers in Canine Plasma

“…We also calculated the anion gap (AG) of canine plasma at pH ϭ 7.40 to be 18.8 mEq/ L; this value was similar to mean estimates obtained previously from large numbers of dogs (AG ϭ 18.3 mEq/L, n ϭ 80; AG ϭ 19 mEq/L, n ϭ 117). 40,41 The results therefore clearly indicate that the AG in healthy dogs essentially reflects the plasma protein concentration. Changes in the AG in diseased dogs may therefore result from changes in the plasma protein concentration or changes in unmeasured strong cation and anion concentrations.…”

Eubicarbonatemic Hydrogen Ion Retention and CKD Progression

“…12 Clinical laboratories list this parameter as "TCO 2 " or "carbon dioxide" and measure its moieties collectively after acidifying the specimen; because HCO 3r epresents~95% of TCO 2 (serum [TCO 2 ] being higher by 1.0-1.5 mEq/L than serum [HCO 3ˉ] ), the terms are usually used interchangeably, most clinicians preferring "serum [ 12 This 8-digit span is substantial, with the largest source of variance being the variance in PCO 2 . [12][13][14] Recently, a frequent large variation in the normal range of serum [HCO 3ˉ] among clinical laboratories was reported, with deviations at one or both ends of the above range (to as low as 18-20 mEq/L and as high as 33-35 mEq/L) and an overall span that can encompass 10 to 13 digits. 12 These substantial deviations from the 23-to 30-mEq/L range are bound to impart confusion to clinicians regarding the diagnosis and management of the metabolic acidosis of CKD.…”

“… 12 This 8-digit span is substantial, with the largest source of variance being the variance in P co 2 . 12 , 13 , 14 Recently, a frequent large variation in the normal range of serum [HCO 3 ˉ] among clinical laboratories was reported, with deviations at one or both ends of the above range (to as low as 18-20 mEq/L and as high as 33-35 mEq/L) and an overall span that can encompass 10 to 13 digits. 12 These substantial deviations from the 23- to 30-mEq/L range are bound to impart confusion to clinicians regarding the diagnosis and management of the metabolic acidosis of CKD.…”