Normal saline intoxication

The overzealous administration of sodium chloride causes a normal anion gap metabolic acidosis by decreasing the strong ion difference. This is the archetypal normal anion gap acidosis.

Previously discussed calculations suggest that every bag of saline increases the serum chloride by 3mmol/L. In Stewarts terms, normal saline has a strong ion difference of 0mmol/L (given how equal the concentrations of sodium and chloride are), and thus adding it to a body fluid will decrease the strong ion difference. The strong ion difference of Hartmanns, on the other hand, is 28mmol/L, and so it has a much gentler acidifying effect.

This has been demonstrated experimentally – in a cohort of 5 septic patients; and the theory is  discussed in detail here.

Change in strong ion difference following the infusion of normal saline

gamblegram of the strong ion difference

The above graph is adopted from Lobo et al, who in 2003 infused a series of healthy volunteers with 2000ml of normal saline to study the difference between sodium chloride and Hartmanns solution.

Now, enough saline-bashing. If we remain faithful to the interpretation of acid base disorders in terms of the strong ion difference, we will find that any other fluid which has a low string ion difference will produce a similar picture; perhaps not by increasing the chloride (if it contains no chloride) but by forcing the body fluid to equilibrate with a fluid which has an SID of 0mmol/L


Skellett, S., et al. "Chasing the base deficit: hyperchloraemic acidosis following 0.9% saline fluid resuscitation." Archives of Disease in Childhood 83.6 (2000): 514-516.

Constable, Peter D. "Hyperchloremic acidosis: the classic example of strong ion acidosis." Anesthesia & Analgesia 96.4 (2003): 919-922.

Reid, Fiona, et al. "Hartmann’s solution: a randomized double-blind crossover study." Clinical Science 104 (2003): 17-24.