We thank Dr. Williams for her interest in our report of subtle, reversible cognitive function and memory changes at hemoglobin concentrations of 6 and 5 g/dl. 1Dr. Williams et al. 2reported anecdotally reported perceived difficulty in abstract thinking in 13 of 18 volunteers to whom 50 ml/kg NaCl, 0.9%, was administered and in none to whom a similar volume of lactated Ringer’s solution was administered. Dr. Williams suggests that their subjective observation might have been caused by a change in sodium or chloride concentrations. However, those values were not outside the normal range, and they did not change significantly in either group, although the difference before and after infusion for sodium concentration differed between the two groups (NaCl, 1 ± 2 mEq/l vs. lactated Ringer’s solution, −1 ± 2 mEq/l). 2
We did not measure serum sodium or chloride concentrations in the subjects in whom we studied cognitive function. 1However, we did measure sodium concentrations in a group of 28 similar subjects in whom we acutely decreased hemoglobin concentration using similar methodology. When hemoglobin concentration was decreased from 12.7 ± 1.0 g/dl to 7.1 ± 0.3 g/dl, sodium concentration significantly increased (P < 0.0001) from 137.6 ± 1.6 to 139.7 ± 1.9 mEq/l. However, we found no changes of cognitive function in our volunteers at a hemoglobin concentration of 7 g/dl. In contrast, with further decrease of the hemoglobin concentration to 5.7 ± 0.3 g/dl, a value within the range in which we detected changes in cognitive function, sodium concentration did not significantly change further (140.2 ± 1.6 g/dl;P = 0.1).
Thus, our data does not seem to support the thought that some or all of the cognitive function changes we noted at hemoglobin concentrations of 6 and 5 g/dl but not at 7 g/dl were related to alterations of serum sodium concentration.
*University of California, San Francisco, California. email@example.com