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Review
. 2017 Sep;31(5):1371-1381.
doi: 10.1111/jvim.14803. Epub 2017 Aug 20.

Effect of Intravenously Administered Crystalloid Solutions on Acid-Base Balance in Domestic Animals

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Free PMC article
Review

Effect of Intravenously Administered Crystalloid Solutions on Acid-Base Balance in Domestic Animals

W Muir. J Vet Intern Med. .
Free PMC article

Abstract

Intravenous fluid therapy can alter plasma acid-base balance. The Stewart approach to acid-base balance is uniquely suited to identify and quantify the effects of the cationic and anionic constituents of crystalloid solutions on plasma pH. The plasma strong ion difference (SID) and weak acid concentrations are similar to those of the administered fluid, more so at higher administration rates and with larger volumes. A crystalloid's in vivo effects on plasma pH are described by 3 general rules: SID > [HCO3-] increases plasma pH (alkalosis); SID < [HCO3-] decreases plasma pH (alkalosis); and SID = [HCO3-] yields no change in plasma pH. The in vitro pH of commercially prepared crystalloid solutions has little to no effect on plasma pH because of their low titratable acidity. Appreciation of IV fluid composition and an understanding of basic physicochemical principles provide therapeutically valuable insights about how and why fluid therapy can produce and correct alterations of plasma acid-base equilibrium. The ideal balanced crystalloid should (1) contain species-specific concentrations of key electrolytes (Na+ , Cl- , K+ , Ca++ , Mg++ ), particularly Na+ and Cl- ; (2) maintain or normalize acid-base balance (provide an appropriate SID); and (3) be isosmotic and isotonic (not induce inappropriate fluid shifts) with normal plasma.

Keywords: Acid-base balance; Base replacement; Fluid therapy; Metabolic acidosis; Physiology.

Figures

Figure 1
Figure 1
Relationship between approximate pH values and mortality in 754 critically ill human patients.21
Figure 2
Figure 2
The different approaches used to diagnose and describe acid‐base disorders can be categorized as descriptive, semiquantitative, and quantitative. The physicochemical (Stewart) approach can be used in all 3 capacities. Atot = total weak acids; PCO 2 = partial pressure of carbon dioxide; SBE = standard base excess; SID = strong ion difference; SIG = strong ion gap.26
Figure 3
Figure 3
Principal independent factors that determine pH.
Figure 4
Figure 4
Strong ion gap (SIG) is the difference SID a and SID e. The SIG is an accurate measure of the unmeasured anions present in plasma.81

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