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Dilution with three different solutions: plasmatic effects and quantity and quality of urinary output


Crystalloids have different electrolyte composition and therefore different strong ion differences (SIDinf). The aim of the study was to investigate the response of the kidney to plasmatic acid-base changes induced by dilution with three crystalloid solutions at different SID.


Six pigs (22 ± 4 kg) were anesthetized and mechanically ventilated. The respiratory rate was adjusted to maintain pCO2 constant. A urinary catheter was placed and connected to a urinary analyzer (Orvim, Paderno Dugnano, Italy) [1]. Pigs were randomly assigned to a sequence of dilutions (10% of body weight in 2 hours, followed by 4 hours of washout period) with the following three fluids: normal saline (NS), SID = 0, [Na] = 154, [Cl] = 154; lactated Ringer's (LR), SID = 29, [Na] = 132, [Cl] = 112; and polysaline RIII (RIII), SID = 55, [Na] = 140, [Cl] = 103. Blood gases and electrolytes as well as urinary pH (pHu), urinary electrolytes and urinary output (UO) were recorded at baseline and at the end of each dilution. Plasmatic SID was defined as [Na] + [K] + 2[Ca] - [Cl] - [Lac]. Variations (d) were defined as baseline - 2-hour value.


Plasmatic changes are consistent with previous in vitro studies [2]. dSID was mainly due to d[Cl]: 9.0 ± 1.7 for NS, no change for LR, -1.5 ± 1.6 for RIII. Of note, while no difference was yet observed for urinary electrolytes and UO, pHu significantly differed between the three solutions. See Table 1.

Table 1


The quality of infused fluids affects greatly the acid-base and electrolyte equilibrium of plasma. This in turn alters the quality of urine (pHu).


  1. Caironi P: Minerva Anestesiol. 2010, 76: 316-324.

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  2. Carlesso E: Intensive Care Med. 2010

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Langer, T., Carlesso, E., Protti, A. et al. Dilution with three different solutions: plasmatic effects and quantity and quality of urinary output. Crit Care 15 (Suppl 1), P86 (2011).

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  • Catheter
  • Lactate
  • Normal Saline
  • Urinary Output
  • Washout Period