title: In vivo conditioning of acid-base equilibrium by crystalloid solutions: an experimental study on pigs.
abstract: OBJECTIVE
  Large infusion of crystalloids may induce acid-base alterations according to their strong ion difference ([SID]). We wanted to prove in vivo, at constant PCO(2), 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.
  
  
  METHODS
  In 12 pigs, anesthetized and mechanically ventilated at PCO(2) ≈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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  Results support the hypothesis that at constant PCO(2), pH changes are predictable from the difference between the [SID] of the infused solution and baseline plasma bicarbonate concentration.
authors.affiliation: Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico di Milano, Università degli Studi, Via Francesco Sforza, 35 20122 Milano, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Langer
authors.forename: E
authors.initials: E
authors.lastname: Carlesso
authors.forename: A
authors.initials: A
authors.lastname: Protti
authors.forename: M
authors.initials: M
authors.lastname: Monti
authors.forename: B
authors.initials: B
authors.lastname: Comini
authors.forename: L
authors.initials: L
authors.lastname: Zani
authors.forename: D T
authors.initials: DT
authors.lastname: Andreis
authors.forename: G E
authors.initials: GE
authors.lastname: Iapichino
authors.forename: D
authors.initials: D
authors.lastname: Dondossola
authors.forename: P
authors.initials: P
authors.lastname: Caironi
authors.forename: S
authors.initials: S
authors.lastname: Gatti
authors.forename: L
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects*; D000704:Analysis of Variance; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D019296:Capnography; D000077324:Crystalloid Solutions; D006863:Hydrogen-Ion Concentration; D007552:Isotonic Solutions / Q000494:pharmacology*; D016014:Linear Models; D011897:Random Allocation; D000077325:Ringer's Lactate; D012965:Sodium Chloride / Q000494:pharmacology; D013552:Swine
chemical_list: D001639:Bicarbonates; D000077324:Crystalloid Solutions; D007552:Isotonic Solutions; D000077325:Ringer's Lactate; D012965:Sodium Chloride