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

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 > [HCO 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) ; (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.

Terms, Definitions, Nomenclature, and Routes of Fluid Administration

“…Anion gap is calculated by the following formula: AG = (Na + + K + ) − (Cl − + HCO3 − ). Anion gap is useful to help narrow down the potential causes of metabolic acidosis ( 4 , 8 ).…”

“…A fluid that contains an electrolyte composition (particularly sodium, potassium, and chloride) that is similar to that found in plasma. A balanced solution should maintain or normalize acid-base balance and be isosmotic and isotonic (i.e., not induce inappropriate fluid shifts) with normal plasma ( 4 , 12 , 13 ). Synonyms: balanced isotonic electrolyte solution, polyionic crystalloid solution , or balanced salt solution .…”

“…This consists of an aqueous solution containing a mixture of electrolytes and a weak acid and its conjugate base. The most common buffers are bicarbonate or organic anions (e.g., lactate, acetate, gluconate) ( 4 ).…”

“…Hyperchloremia accompanied by hypobicarbonatemia and metabolic acidosis. Two different mechanistic explanations are bicarbonate loss or dilution (Henderson-Hasselbalch approach) ( 13 ) or a decrease in SID caused by an increase in chloride (i.e., 0.9% Na + Cl − ) ( 4 , 13 , 75 ). Synonym: normal anion gap acidosis .…”

Anesthesia-Associated Relative Hypovolemia: Mechanisms, Monitoring, and Treatment Considerations

“…and highly likely to be species-dependent, highlighting the importance of personalizing fluid resuscitation protocols. Taken together these studies suggest that: (1) goal-directed fluid therapy is superior to “rules of thumb” (e.g., 3 mL crystalloid/1 mL blood loss) or standardized formulas (3–10 mL/kg/h); (2) a balanced crystalloid solution ( 201 ), is the best first choice fluid unless laboratory data suggest otherwise; (3) monitoring techniques should include at least one validated dynamic index [e.g., PPV ( 165 , 170 , 171 , 173 )]; (4) an IV fluid bolus should not exceed 20–30 mL/kg ( 199 ); and (5) maximal rates of fluid administration should range from 0.02 (maintenance) to 1.0 mL/kg/min (resuscitation) during anesthesia ( 200 ).…”