Avoiding common problems associated with intravenous fluid therapy

To the Editor: A recent review of medical textbooks found that the topic of intravenous fluid therapy is poorly covered.1 Hence, the recent article by Hilton and colleagues provides interesting hypothetical examples of the risk of hypovolaemia and hypervolaemia, as well as imbalances in fluid tonicity, in patients receiving intravenous fluid therapy.2 In particular, the authors recommend the use of intravenous 0.9% saline, as it is reportedly isotonic and hence avoids potential imbalances in serum sodium concentration.

However, Hilton and colleagues discuss only tonicity as the determining factor when selecting the type of fluid to give patients. They do not mention that 0.9% saline, also known as “normal” saline, distorts fluid, electrolyte and acid–base balance, despite being isotonic. In healthy subjects, 25% more volume is retained 6 hours after infusion of 2 L of 0.9% saline compared with 2 L of Hartmann’s solution.3 Infusion of 0.9% saline also results in hyperchloraemia, which decreases glomerular filtration rate, and is not seen with infusion of Hartmann’s solution.3

Certainly, the most important side effect of 0.9% saline infusion is metabolic acidosis, caused (according to the Stewart approach) by a reduction in the strong ion difference.4 Using the Stewart approach once again, Hartmann’s solution is “balanced”, ensuring the eradication of infusion-related metabolic acidosis.4

Although tonicity is important in considering the appropriate intravenous fluid therapy, it should not take precedence in the choice of therapy. Such an approach ignores the volume, electrolyte and acid–base disturbances induced by 0.9% saline infusions.