Fluid Management

Question 1

Why normal saline can cause hyperchloremic metabolic acidosis?

Answer 1

Accord- ing to Stewart’s approach, the plasma acid–base status is based on three parameters: the strong ion difference (SID), the arterial partial pressure of carbon dioxide (PaCO2), and the total anion charge of all weak plasma acids (Atot). In this approach bicarbonate does not define acid–base disturbances. SID is a simple calculation of the difference in charge between the strong cations (i.e., Na+, K+, Ca++, Mg++) and strong anions (i.e., Cl , lactate, ketoacids, sulfates). Whereas the SID of plasma is around 40, the SID of normal saline is 0. Infusion of a solution with SID lower than plasma will lead to a decrease in plasma SID and metabolic acidosis because of the relative increase in [Cl ] concentration at the expense of [HCO3 ]. As such, resuscitation with low-SID solutions such as normal saline will inevitably lead to a hyperchloremic metabolic acidosis. Further consequences of normal saline–induced acidosis include the risk of increased plasma potassium because of cellular shifts. Potassium levels have been reported to be similar or higher than baseline using normal saline compared with balanced solutions, even if the balanced solutions contain a low concentration of potassium

Question 2

Besides hyperchloremic metabolic acidosis, which other negative effects may be associated with normal saline?

Answer 2

Major adverse kidney morbidity in acutely and critically ill patients, increased coagulopathy, increased inflammation, and higher postoperative morbidity.

The increase in plasma chloride concentration after infusion of normal saline has been proposed as a mechanism for increased risk of acute kidney injury because of chloride-inducing vasoconstriction of the glomerular afferent arteriole and potentially decreased renal blood flow

Question 3

Perioperative fluid manage considerations

Answer 3

• Use balanced crystalloid solutions instead of normal saline
• Avoid hydroxyethyl starch solutions because of potential nephrotoxicity
• If considering albumin administration, recall that potential benefit is unclear and cost is higher than crystalloids
• Avoid fluid overload, but consider that restrictive fluid practices are associated with increased risk of acute
kidney injury
• Consider use of advanced hemodynamic monitoring to assess fluid responsiveness and guide fluid administration in high-risk patients undergoing major surgery