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Intravenous Fluids

Chandler Montgomery


Indications for intravenous fluid

  • Restoration or maintenance of tissue perfusion

  • Correction of electrolyte abnormalities

  • Nutritional supplementation in those without reliable enteric access

Categorized into crystalloids and colloids

  • Crystalloid = water + electrolytes

  • Colloid = water + proteins/large molecules

Terms

  • Osmolarity: osmoles of solute per L of solution

  • Tonicity: ability to induce movement of water across a membrane

  • Buffer: anions such as lactate, acetate, gluconate which are metabolized to bicarbonate in vivo with the goal of sustaining normal plasma pH

Crystalloids

  • Isotonic fluids used for volume resuscitation
  • After ~ 30 mins, redistribute such that only 25% remains w/in intravascular space

  • Balanced solutions (ex: Lactated Ringer’s, Plasma-Lyte)= have electrolytes concentrations similar to plasma

  • NS may lead to renal vasoconstriction, AKI, hemodynamic instability, increased mortality

    • SMART and SALT-ED: balanced solutions had lower rates of death, new renal replacement therapy, or persistent renal dysfunction compared to NS
  • Situations where NS may be preferred:

    • Cerebral edema/traumatic brain injury

    • Hypovolemic hyponatremia

    • Pre-existing hypochloremic metabolic alkalosis (e.g. after vomiting or over diuresis)

  • Notes on LR

    • The small amount of K in LR (~4 mEq/L) is unlikely to significantly exacerbate hyperkalemia

    • Lactate in LR is sodium lactate. No hydrogen ions are being added to plasma

Common crystalloid solutions:

Fluid Na Cl K Ca Mg Glucose Buffer Osmolarity Tonicity
Plasma ~140 ~100 ~4 ~2.4 1.0 ~0.85 Bicarb ~24 ~290 NA
Normal 0.9% saline 154 154 0 0 0 0 0 308 Isotonic
Lactated Ringer’s 130 109 4.0 2.7 0 0 Lactate 28 273 Isotonic

Plasma-Lyte/

Normosol

140 98 5.0 0 3.0 0

Gluconate 23

Acetate 27

295 Isotonic
D5W + 150 mEq HCO3- 150 0 0 0 0 50 Bicarb 150 300 Isotonic
3% Saline 513 513 0 0 0 0 0 1026 Hypertonic
D5W 0 0 0 0 0 50 0 252 Hypotonic

Colloids

  • Albumin: extracted from human plasma

  • 5% - Used after plasma exchange

  • 25% - raises oncotic pressure and restore intravascular volume

    • Uses: Post-LVP, diagnosis and treatment of hepatorenal syndrome, SBP (see Hepatology)

    • Evidence base for use outside of above indications is poor (SAFE trial)

  • Blood Products: Packed RBCs, FFP, cryoprecipitate, etc