Quimica Ph

Intensive Care Med (2012) 38:686–693 DOI 10.1007/s00134-011-2455-2

EXPERIMENTAL

T. Langer E. Carlesso A. Protti M. Monti B. Comini L. Zani D. T. Andreis G. E. Iapichino D. Dondossola P. Caironi S. Gatti L. Gattinoni

In vivo conditioning of acid–base equilibrium by crystalloid solutions: an experimental study on pigs

Received: 24 August 2011 Accepted: 24 November 2011 Published online:25 January 2012 Ó Copyright jointly held by Springer and ESICM 2012 Electronic supplementary material The online version of this article (doi:10.1007/s00134-011-2455-2) contains supplementary material, which is available to authorized users.

P. Caironi Á L. Gattinoni Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS Ca’ Granda OspedaleMaggiore Policlinico di, Milano, Italy

Abstract Purpose: Large infusion of crystalloids may induce acid-base alterations according to their strong ion difference ([SID]). We wanted to prove in vivo, at constant PCO2, that if the [SID] of the infused crystalloid is equal to baseline plasma bicarbonate, the arterial pH remains unchanged, if lower it decreases, and T. Langer Á E. Carlesso Á A.Protti Á if higher it increases. Methods: In M. Monti Á B. Comini Á L. Zani Á 12 pigs, anesthetized and mechaniD. T. Andreis Á G. E. Iapichino Á cally ventilated at PCO2 &40 mmHg, P. Caironi Á L. Gattinoni ()) Dipartimento di Anestesiologia, 2.2 l of crystalloids with a [SID] Terapia Intensiva e Scienze similar to (lactated Ringer’s Dermatologiche, Fondazione IRCCS Ca’ 28.3 mEq/l), lower than (normalsalGranda Ospedale Maggiore Policlinico ine 0 mEq/l), and greater than ` di Milano, Universita degli Studi, (rehydrating III 55 mEq/l) baseline Via Francesco Sforza, 35 bicarbonate (29.22 ± 2.72 mEq/l) 20122 Milano, Italy were infused for 120 min in rane-mail: gattinon@policlinico.mi.it Tel.: ?39-02-55033232 domized sequence. Four hours of Fax: ?39-02-55033230 wash-out were allowed between theinfusions. Every 30 min up to minute D. Dondossola Á S. Gatti Centro di Ricerche Chirurgiche Precliniche, 120 we measured blood gases, plasma electrolytes, urinary volume, pH, and Fondazione IRCCS Ca’ Granda Ospedale electrolytes. Albumin, hemoglobin, Maggiore Policlinico di Milano, and phosphates were measured at Milan, Italy

time 0 and 120 min. Results: Lactated Ringer’s maintained arterial pHunchanged (from 7.47 ± 0.06 to 7.47 ± 0.03) despite a plasma dilution around 12%. Normal saline caused a reduction in pH (from 7.49 ± 0.03 to 7.42 ± 0.04) and rehydrating III induced an increase in pH (from 7.46 ± 0.05 to 7.49 ± 0.04). The kidney reacted to the infusion, minimizing the acidbase alterations, by increasing/ decreasing the urinary anion gap, primarily by changing sodium and chlorideconcentrations. Lower urine volume after normal saline infusion was possibly due to its greater osmolarity and chloride concentration as compared to the other solutions. Conclusions: Results support the hypothesis that at constant PCO2, pH changes are predictable from the difference between the [SID] of the infused solution and baseline plasma bicarbonate concentration. Keywords Crystalloidsolutions Á Acid-base equilibrium Á Stewart’s approach Á Volume resuscitation Á Animal study

687

Introduction
Fluid resuscitation with large amounts of crystalloids is usual in critically ill patients, and normal saline is the most widely used solution for this purpose. It has been observed that large amounts of normal saline induce metabolic acidosis [1–3]. According to misinterpreted Stewart’smodel [4, 5], this metabolic acidosis is due to a reduction in the plasma strong ion difference ([SID]). However, to fully understand the relationship among the dilution, kind of solution, and acid-base equilibrium, all three independent variables of Stewart’s model must be considered together, not only [SID], but also PCO2 and the total amount of weak acids [ATOT] [6]. Normal pH is assured by an...