Intensive Care Medicine

, 35:2033 | Cite as

Dilutional acidosis: where do the protons come from?

  • Luciano Gattinoni
  • E. Carlesso
  • G. Maiocchi
  • F. Polli
  • P. Cadringher



To investigate the mechanism of acidosis developing after saline infusion (dilutional acidosis or hyperchloremic acidosis).


We simulated normal extracellular fluid dilution by infusing distilled water, normal saline and lactated Ringer’s solution. Simulations were performed either in a closed system or in a system open to alveolar gases using software based on the standard laws of mass action and mass conservation. In vitro experiments diluting human plasma were performed to validate the model.


In our computerized model with constant pKs, diluting extracellular fluid modeled as a closed system with distilled water, normal saline or lactated Ringer’s solution is not associated with any pH modification, since all its determinants (strong ion difference, CO2 content and weak acid concentration) decrease at the same degree, maintaining their relative proportions unchanged. Experimental data confirmed the simulation results for normal saline and lactated Ringer’s solution, whereas distilled water dilution caused pH to increase. This is due to the increase of carbonic pK induced by the dramatic decrease of ionic strength. Acidosis developed only when the system was open to gases due to the increased CO2 content, both in its dissociated (bicarbonate) and undissociated form (dissolved CO2).


The increase in proton concentration observed after dilution of the extracellular system derives from the reaction of CO2 hydration, which occurs only when the system is open to the gases. Both Stewart’s approach and the traditional approach may account for these results.


Stewart’s approach Acid–base equilibrium Metabolic acidosis Volume resuscitation CO2 content 

Supplementary material

134_2009_1653_MOESM1_ESM.doc (127 kb)
(DOC 127 kb)


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Copyright information

© Copyright jointly hold by Springer and ESICM 2009

Authors and Affiliations

  • Luciano Gattinoni
    • 1
    • 2
  • E. Carlesso
    • 2
  • G. Maiocchi
    • 3
  • F. Polli
    • 2
  • P. Cadringher
    • 2
  1. 1.Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del DoloreFondazione IRCCS, “Ospedale Maggiore Policlinico Mangiagalli Regina Elena” di MilanoMilanItaly
  2. 2.Dipartimento di Anestesiologia, Terapia Intensiva e Scienze DermatologicheUniversità degli StudiMilanItaly
  3. 3.Unità Operativa Complessa di FarmaciaFondazione IRCCS, “Ospedale Maggiore Policlinico Mangiagalli Regina Elena”di MilanoItaly

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