To the Editor.
—In a paper entitled "Utilization of Osmometry in Critically Ill Surgical Patients" (Arch Surg 102:363, 1971) Boyd et al reported that the measured serum osmolality in critically ill surgical patients tends to be up to about 100 mOsm/liter higher than the value calculated from measured serum sodium, blood urea nitrogen (BUN), and glucose according to the following formula:The difference between the measured serum osmolality and the calculated Sosm is called mOsm-D. The authors point out that "The correlation of the Sosm and the mOsm-D with lactate has been shown to be good (r = 0.793) in late stages of traumatic shock." Furthermore, "Some of the osmolal elevation (25 to 50 mOsm/kg) is probably due to lactic acid accumulating during hemorrhagic hypotension."In the opinion of the undersigned, the accumulation of lactic acid during shock influences neither the