Intensive Care Medicine

, Volume 37, Issue 3, pp 461–468 | Cite as

The rule regulating pH changes during crystalloid infusion

  • E. Carlesso
  • G. Maiocchi
  • F. Tallarini
  • F. Polli
  • F. Valenza
  • P. Cadringher
  • L. Gattinoni



To define the rule according to which crystalloid solutions characterized by different strong ion difference (SID) modify the acid–base variables of human plasma.


With a previously validated software, we computed the effects of diluting human plasma with crystalloid solutions ([SID] 0–60, 10 mEq/l stepwise). An equation was derived to compute the diluent [SID] required to maintain the baseline pH unchanged, at constant PCO2 and at every dilution fraction. The results were experimentally tested using fresh frozen plasma, re-warmed at 37°C, equilibrated at PCO2 35 and 78 mmHg, at baseline and after the infusion of crystalloid solutions with 0, 12, 24, 36, 48 mEq/l [SID].


The mathematical analysis showed that the diluent [SID] required to maintain unmodified the baseline pH equals the baseline bicarbonate concentration, [HCO3], assuming constant PCO2 throughout the process. The experimental data confirmed the theoretical analysis. In fact, at the baseline [HCO3] of 18.3 ± 0.3 mmol/l (PCO2 35 mmHg) the pH was 7.332 ± 0.004 and remained 7.333 ± 0.003 when the diluting [SID] was 18.5 ± 0.0 mEq/l. At baseline [HCO3] of 19.5 ± 0.3 mmol/l (PCO2 78 mmHg) the pH was 7.010 ± 0.003 and remained 7.004 ± 0.003 when the diluting [SID] was 19.1 ± 0.1 mEq/l. At both PCO2 values infusion with [SID] lower or greater than baseline [HCO3] led pH to decrease or increase, respectively.


The baseline [HCO3] dictates the pH response to crystalloid infusion. If a crystalloid [SID] equals baseline [HCO3], pH remains unchanged at constant PCO2, whereas it increases or decreases if the [SID] is greater or lower, respectively.


Acid–base equilibrium Volume resuscitation Stewart’s approach Balanced solution Crystalloids 



We deeply thank A. De Mori S.p.A., Italy, that kindly provided the blood gas analyzer and tonometer used for the in vitro experiments.

Supplementary material

134_2010_2095_MOESM1_ESM.doc (208 kb)
Supplementary material 1 (DOC 208 kb)


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Copyright information

© Copyright jointly held by Springer and ESICM 2010

Authors and Affiliations

  • E. Carlesso
    • 2
  • G. Maiocchi
    • 3
  • F. Tallarini
    • 2
  • F. Polli
    • 1
  • F. Valenza
    • 1
    • 2
  • P. Cadringher
    • 2
  • L. Gattinoni
    • 1
    • 2
  1. 1.Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del DoloreFondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico di MilanoMilanItaly
  2. 2.Dipartimento di Anestesiologia, Terapia Intensiva e Scienze DermatologicheUniversità degli StudiMilanItaly
  3. 3.Unità operativa complessa di FarmaciaFondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico di MilanoMilanItaly

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