Normal saline admin: Lab findings

Basic, Clinical Sciences: Anesthesia Procedures, Methods, and Techniques

Administration of normal saline (NS) can have a wide variety of clinical effects.  NS contains sodium and chloride ions in levels above that of blood (154 and 154 for sodium and chloride versus 140 and 104 for a typical healthy human).  Thus, giving a patient NS will cause both of these clinical values to increase; this increase is more pronounced for chloride than for sodium given the larger difference between physiologic normal and fluid levels.  The increase in plasma chloride impairs bicarbonate resorption in the kidneys, which leads to increased bicarbonate loss and therefore non-anion gap metabolic acidosis.  This hyperchloremic acidosis will cause a potassium shift out of the cell and can paradoxically cause hyperkalemia despite not containing any potassium.  Finally, normal saline will decrease plasma protein concentrations in blood through a dilutional effect.

Normal Saline:

Increased:

• Serum sodium

• Serum chloride

• Serum hydrogen ion

• Serum potassium

Decreased:

• pH

• Anion gap

• Plasma proteins

Updated definition 2020:

  • Rapid and excess administration of normal saline leads to a hyperchloremic non anion gap metabolic acidosis. NS contains 154 mEq/L of both Na+ and Cl-, therefore both serum [Na+] and [Cl-] will be increased.
  • Acidosis is due to a decreased strong ion difference (SID). SID = [strong cations] - [strong anions]. NS has a SID of zero; [154] - [154] = 0. In plasma, SID = [Na+ + K+ + Ca2+ + Mg2+] - [Cl- + lactate- + albumin- + PO43-] = +40-44 mEq/L. The steep rise in [Cl-] decreases the strong ion difference.
  • Excessive Cl- impairs bicarb reabsorption in the kidneys, and serum [HCO3-] decreases. This decrease compensates the increased [Cl-], leading to a non-gap acidosis.
  • Treatment: IV administration of a crystalloid solution with a high SID, such as NaHCO3 or tromethamine.

73%

Answered correctly

2020

Year asked

77%

Answered correctly

2018

Year asked

Author
Eric Ness, MD and Christine Orser, MD