In vivo conditioning of acid–base equilibrium by crystalloid solutions: an experimental study on pigs
- 421 Downloads
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 if higher it increases.
In 12 pigs, anesthetized and mechanically ventilated at PCO2 ≈40 mmHg, 2.2 l of crystalloids with a [SID] similar to (lactated Ringer’s 28.3 mEq/l), lower than (normal saline 0 mEq/l), and greater than (rehydrating III 55 mEq/l) baseline bicarbonate (29.22 ± 2.72 mEq/l) were infused for 120 min in randomized sequence. Four hours of wash-out were allowed between the infusions. Every 30 min up to minute 120 we measured blood gases, plasma electrolytes, urinary volume, pH, and electrolytes. Albumin, hemoglobin, and phosphates were measured at time 0 and 120 min.
Lactated Ringer’s maintained arterial pH unchanged (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 acid-base alterations, by increasing/decreasing the urinary anion gap, primarily by changing sodium and chloride concentrations. Lower urine volume after normal saline infusion was possibly due to its greater osmolarity and chloride concentration as compared to the other solutions.
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.
KeywordsCrystalloid solutions Acid-base equilibrium Stewart's approach Volume resuscitation Animal study
We are grateful to Fabio Ambrosetti for his technical support, to GE Healthcare for providing mechanical ventilators, to A. De Mori S.p.A., Italy, who kindly provided the blood gas analyzer, and to Roberto Castenetto for technical support with the KING analyzer. This study was supported in part by an Italian grant provided by Fondazione Fiera di Milano for Translational and Competitive Research (2007, Luciano Gattinoni).
- 3.O’Malley CM, Frumento RJ, Hardy MA, Benvenisty AI, Brentjens TE, Mercer JS, Nett-Guerrero E (2005) A randomized, double-blind comparison of lactated Ringer’s solution and 0.9% NaCl during renal transplantation. Anesth Analg 100:1518–1524, tableGoogle Scholar
- 10.Institute of Laboratory Animal Resources ColSNRC (1996) Guide for the care and use of laboratory animals. National Academy Press, WashingtonGoogle Scholar
- 11.Protti A, Cressoni M, Santini A, Langer T, Mietto C, Febres D, Chierichetti M, Coppola S, Conte G, Gatti S, Leopardi O, Masson S, Lombardi L, Lazzerini M, Rampoldi E, Cadringher P, Gattinoni L (2011) Lung stress and strain during mechanical ventilation: any safe threshold? Am J Respir Crit Care Med 183:1354–1362PubMedCrossRefGoogle Scholar
- 21.Bagshaw SM, Lapinsky S, Dial S, Arabi Y, Dodek P, Wood G, Ellis P, Guzman J, Marshall J, Parrillo JE, Skrobik Y, Kumar A (2009) Acute kidney injury in septic shock: clinical outcomes and impact of duration of hypotension prior to initiation of antimicrobial therapy. Intensive Care Med 35:871–881PubMedCrossRefGoogle Scholar