Acidosis in the Critically Ill: Interpretation and Significance

  • J. A. Kellum


To the clinician acidosis is the increased production and/or decreased elimination of acid by the body. To the biochemist or the physiologist acidosis is a process that increases the concentration of hydrogen ion (H+) in a solution (such as blood). At first glance, this distinction seems minor, but its implications are enormous. The most important implication is that acidosis is not merely the addition (or the decreased elimination) of H+. One simple example of this is respiratory acidosis. The body “eliminates” most of its H+ by eliminating CO2. Yet CO2 does not contain H+. Where does the H+ go? The answer is that it becomes water (H+ + HCO 3 - → H2CO3 → CO2 + H2O). This answer seems satisfactory until one asks how an increase in CO2 produces an increase in H+ concentration. The answer is that CO2 is in equilibrium with HCO 3 - and thus an increase in CO2 produces an increase in H+ and HCO3” (i.e., the reaction is reversible). Here we see that the change in CO2 produces a change in H+ concentration. The H+ itself comes from the dissociation of water. This chapter will focus on the other determinates of H+ concentration in biologic solutions and the clinical effects of changes in these determinants.


Acute Lung Injury Metabolic Acidosis Circ Shock Fixed Acid Unmeasured Anion 
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© Springer-Verlag Italia, Milano 1996

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  • J. A. Kellum

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