hyperchloremic metabolic acidosis from normal saline
- related: Nephrology
- tags: #literature #nephrology
After operations with high volumes of blood loss, patients can arrive in the ICU with a hyperchloremic metabolic acidosis due to the rapid infusion of high volumes of normal saline. Typically, this is a self-limited problem that will resolve without intervention. The acid-base status needs only to be followed to make sure it normalizes appropriately (choice A is correct). Attempting to correct the acidosis with exogenous sodium bicarbonate can have the effect of leading to overshoot metabolic alkalosis (choice B is incorrect). Administration of additional normal saline will only make the acidosis worse, as the total intravascular concentration of chloride rises (choice C is incorrect). Acetazolamide is a carbonic anhydrase inhibitor that increases sodium bicarbonate excretion from the kidneys, which would worsen this metabolic acidosis (choice D is incorrect).
Our understanding of the physiology of metabolic acidosis due to hyperchloremia after large-volume normal saline resuscitation is based on the concept of dissociation equilibrium proposed by Stewart, which postulates that hydrogen ion concentration is dependent on the strong ion difference (SID), the effect of weak plasma acids (Prot-) and the PaCO2, which can be calculated with two equations (PaCO2 is measured).
Prot- = serum total protein concentration (g/dL) × 2.34 (a constant derived to reflect the proportion of serum proteins that carry a charge).
On the basis of Stewart’s equations, Scheingraber and colleagues were able to deduce that the most significant causes of acidosis seen after large-volume blood loss surgery with resuscitation with normal saline were due to elevated chloride levels and loss of serum proteins during surgery. Because their trial compared normal saline with lactated Ringer’s solution (where protein dropped in both groups), they showed that the difference in postoperative pH was the result of only the elevated chloride ion. This study also demonstrated that the effect was self-limited and did not require treatment.123