A Physicochemical Model of Crystalloid Infusion on Acid-Base Status

Abstract

The objective of this study is to develop a physicochemical model of the projected change in standard base excess (SBE) consequent to the infused volume of crystalloid solutions in common use. A clinical simulation of modeled acid-base and fluid compartment parameters was conducted in a 70-kg test participant at standard physiologic state: pH =7.40, partial pressure of carbon dioxide (PCO2) = 40 mm Hg, Henderson-Hasselbalch actual bicarbonate ([HCO3]HH) = 24.5 mEq/L, strong ion difference (SID) = 38.9 mEq/L, albumin = 4.40 g/dL, inorganic phosphate = 1.16 mmol/L, citrate total = 0.135 mmol/L, and SBE =0.1 mEq/L. Simulations of multiple, sequential crystalloid infusions up to 10 L were conducted of normal saline (SID = 0), lactated Ringer's (SID = 28), plasmalyte 148 (SID = 50), one-half normal saline þ 75 mEq/L sodium bicarbonate (NaHCO3; SID = 75), 0.15 mol/L NaHCO3 (SID = 150), and a hypothetical crystalloid solution whose SID = 24.5 mEq/L, respectively. Simulations were based on theoretical completion of steady-state equilibrium and PCO2 was fixed at 40 mm Hg to assess nonrespiratory acid-base effects. A crystalloid SID equivalent to standard state actual bicarbonate (24.5 mEq/L) results in a neutral metabolic acid-base status for infusions up to 10 L. The 5 study solutions exhibited curvilinear relationships between SBE and crystalloid infusion volume in liters. Solutions whose SID was greater than 24.5 mEq/L demonstrated a progressive metabolic alkalosis and less, a progressive metabolic acidosis. In a human model system, the effects of crystalloid infusion on SBE are a function of the crystalloid and plasma SID, volume infused, and nonvolatile plasma weak acid changes. A projection of the impact of a unit volume of various isotonic crystalloid solutions on SBE is presented. The model's validation, applications, and limitations are examined.

Fluid Replacement in Craniofacial Pediatric Surgery

“…14 It is the net unbalanced positive charge on the strong ions present in the solution that is balanced by the net charge on all other weak ions. 15 In normal plasma, SID has a numerical value of approximately 40.…”

The Myth of 0.9% Saline

“…Stewart's hypothesis emphasizes electroneurtrality and when differences are present in between the cations and anions, the body converts water (H 2 O) into hydrogen ion and bicarb accordingly to maintain electroneutrality. [8][9][10] In the original equation, strong ions include sodium, chloride, and other electrolytes such as potassium and magnesium; these other electrolytes are much less in concentration, therefore not enough to cause a physiological effect. In terms of acid-base physiology in Peter Stewart's approach, the SID is usually effectively the difference between sodium and chloride.…”

“…(Although hyperphosphatemia is one condition where phosphate increases so much that it can alter the SID.) [8][9][10] When the SID increases, the serum pH becomes alkalinized and when the difference decreases, the opposite effect occurs. NS's Na:Cl ratio is 1:1 with an SID of 0; therefore, when large volumes are infused, serum acidosis results.…”

“…NS's Na:Cl ratio is 1:1 with an SID of 0; therefore, when large volumes are infused, serum acidosis results. [8][9][10] More balanced solutions with less chloride including lactate Ringer and Normosol/PlasmaLyte have SIDs ranging from 21 to 42 and have less of an acidotic effect when infused in large volumes [8][9][10] (see the Table).…”

Whole body acid-base and fluid-electrolyte balance: a mathematical model

“…Their model was primarily used to examine the effects of respiratory disturbances on blood acidbase balance. Later, the Stewart approach was used by Omron and Omron (29) to formulate a simplified whole-body model that determined the change in acid-base status due to crystalloid infusions.…”