Acidosis in the Critically Ill: Interpretation and Significance
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.
KeywordsAcute Lung Injury Metabolic Acidosis Circ Shock Fixed Acid Unmeasured Anion
Unable to display preview. Download preview PDF.
- 1.Stewart P (1981) How to understand acid-base: a quantitative acid-base primer for biology and medicine. Elsevier, New YorkGoogle Scholar
- 2.Narins RG, Jones ER, Townsend R, Goodkin DA, Shay RJ (1985) Metabolic acid-base disorders: pathophysiology, classification and treatment. In: Arieff AI, DeFronzo RA (eds) Fluid, electrolyte, and acid-base disorders. Churchill Livingstone, New York, pp 269–384Google Scholar
- 12.Bellomo R, Ondulick B, Kellum J, Pinsky MR (1994) Visceral lactate fluxes during early endotoxemia in the dog. Am J Respir Crit Care Med 149:A413Google Scholar
- 15.Gutierrez G, Clark C, Nelson C, Tiu A, Brown S (1993) The lung as a source of lactate in sepsis and ARDS. Chest 104:S12Google Scholar
- 17.Lee KH, Rico P, Ondulick BW, Pinsky MR (1995) Hydrochloric acid-induced lung injury is not associated with a positive lung lactate flux. Am J Respir Crit Care Med 151:A761Google Scholar
- 29.Kellum JA, Bellomo R, Kramer DJ, Pinsky MR (1995) Etiology of metabolic acidosis during sahne resuscitation in edotoxemia. Am J Respir Crit Care Med 151:A318Google Scholar
- 30.Guggenheim EA (1957) Thermodynamics, an advanced treatment for chemists and physicists. North-Holland, Amsterdam, pp 378–382Google Scholar
- 32.Fiddian-Green R (1989) Splanchnic ischemia and multiple organ failure. Mosby, London, pp 349–363Google Scholar
- 34.Montgomery A, Almquist P, Arvidsson D et al (1990) Early detection of gastrointestinal mucosal ischemia in porcine E. coli sepsis. Acta Chir Scand 156:613–620Google Scholar