Saline infusion, acidosis, and the Stewart approach.

To the Editor:-The report by Scheingraber et al.’ highlights the phenomenon of acidemia after infusion of 0.9%) saline in the perioperative period. The accompanying editorial’ discusses several relevant points; however, we are disappointed that neither the article nor the editorial addresses the central issue of the relative merits of the Stewart approachg in describing acidbase physiology and pathophysiology. Compared with the Henderson-Hasselbalch approach, the Stewart approach has a number of appealing features. (1) The control of acidbase and water homeostasis can be explained in terms of both sodium and chloride regulation. (2) Acid-base status is partly controlled by a number of plasma electrolytes, notably sodium and chloride. These electrolytes can be manipulated in the clinical setting to optimize acid-base status. (3) The factors controlling acidbase status are independent. Criticisms of the Henderson-Haselbalch approach include a lack of independence between carbon dioxide and bicarbonate.4 (4) The Henderson-Hasselbalch approach does not allow assessment of nonvolatile buffers, whereas the Stewart approach explicitly includes assessment of weak acids.4 Comparison of the Stewart and Henderson-Hasselbalch approaches is complicated by the fact that both approaches adequately describe the acidbase end point, as Scheingraber et al. demonstrate.’ Further study is required to determine which approach better describes the mechanisms of acidbase physiology. Previous animal studies5 have suggested that the alkalinizing effect of lactate-containing solutions in acute resuscitation is time dependent, which underscores the concept of lactate as a strong ion. The removal of lactate from the circulation will increase the strong ion difference and reduce acidosis.3 This effect may be supplemented by further increases in the strong ion difference associated with lactate metabolism”; in contrast, added chloride ions appear to persist longer in the circulation. Subsequently, a smaller strong ion difference is maintained along with greater acidosis, as seen in the report by Scheingraber et al.‘ David A. Story, M.B.B.S.(Hon), B.M.Sci(Hon), F.A.N.Z.C.A. Staff Anaesthetist Department of Anaesthesia [email protected]. edu.au Frank Liskaser, M.B.B.S., F.A.N.Z.C.A. Staff Anaesthetist Department of Anaesthesia Rinaldo Bellorno, M.B.B.S., M.D., F.R.A.C.P. Associate Professor Intensivist and Director of Research Department of Intensive Care Austin and Repatriation Medical Centre Austin Hospital Heidelberg Melbourne, Victoria 3084, Australia