Monthly Archives: October 2022

BALANCED SALT SOLUTIONS

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  • Intravenous “balanced” solutions include crystalloids and colloids with minimal effect on the homeostasis of the extracellular compartment, and in particular on acid–base equilibrium and electrolyte concentrations. These are fluids which are able to leave the plasma pH unchanged after its administration.
  • There are two main categories of balanced solutions : (1) fluids causing a minimal effect on acid–base equilibrium, having an electrolyte content with an in vivo strong ion difference (SID), i.e., the SID after metabolism of the organic anion, close to 24–29 mEq/L; (2) fluids having a normal or sub-normal Cl−content(Cl− ≤ 110 mEq/L).
  • The ideal balanced solution should have an in vivo SID equal to the baseline concentration of HCO3−. If the SID of the infused fluid is greater than plasma HCO3−, plasma pH will tend toward alkalosis; if the SID of the infused fluid is lower than plasma HCO3−, plasma pH will tend toward acidosis, as it is always the case for NaCl 0.9%.
  • An isotonic balanced solution leaving unaltered acid–base equilibrium (i.e., with an SID close to 24 mEq/L) will necessarily have a Cl− content > 110 mEq/L (as in Sterofundin-ISO).
  • In contrast, a fluid with an SID of 24 mEq/L and a lower Cl−content will necessarily be slightly hypotonic (as with Lactated Ringer’s). Finally, an isotonic fluid with a low Cl−content will necessarily have a higher SID (as with PlasmaLyte), with a consequent alkalizing effect.
  • Chloride-rich NaCl 0.9% causes a higher dose-dependent degree of acidosis and hyperchloremia, which possibly favors the contraction of vascular smooth muscles, potentially leading to a reduced renal perfusion.
  • Hyperchloremia may cause increased tubule-glomerular feedback and decreased renal cortical perfusion. NaCl 0.9%, being slightly hypertonic, likely causes an increased incretion of arginine vasopressin.
  • These effects can conceivably contribute to the slower renal excretion of NaCl 0.9% as compared to balanced solutions. Indeed, more fluid will be retained in the interstitial space, with the consequent propensity to cause more edema.
  • Therefore, the use of balanced solutions, particularly in patients that potentially need a significant amount of intravenous fluids, seems to be a reasonable pragmatic choice.
  • On the contrary, saline may be an intuitive choice for patients with hypovolemic hyponatremia or hypochloremic metabolic alkalosis.
  • In any other settings, the most important reason to choose NaCl 0.9% over balanced solutions is likely economic in nature. Therefore, the patient’s serum chloremia is an important factor to determine the appropriate type of fluids