Background: Popular intravenous fluids in clinical use may have an impact on electrolyte concentration and metabolic balance and should be considered as powerful pharmacological agents. There is a growing body of evidence that fluid therapy should be more individualised and preferably based on balanced solutions.

Aim: We sought to investigate the impact of three commonly used balanced fluids on electrolytes and metabolic equilibrium in an in vitro setting.

Methods: Study group comprised 32 healthy male volunteers (without history of any acute/chronic disorder or known metabolic abnormality), aged 21–35 (29 ± 4) years, weight 59–103 (81.2 ± 9.8) kg, from whom blood samples were withdrawn. The whole blood was diluted in 4:1 ratio with the study solutions to make an end-concentration of 20 vol.% of each solution. The test solutions included balanced crystalloid (Plasmalyte^®, Baxter, Poland [PL]), succinylated gelatin (Geloplasma^®, Fresenius Kabi, Poland [GEL]) and 6% HES 130/0.4 (Volulyte^®, Fresenius Kabi, Poland [HES]).

Results: All fluids caused comparable degree of haemodilution. PL and GEL decreased (104 mmol/L, interquartile range [IQR] 103–105; and 106 mmol/L, IQR 105–107.5, respectively), whereas HES increased the concentration of Cl– to 109 (IQR 108–110) mmol/L. PL and HES decreased (136, IQR 136–137 mmol/L; and 138 mmol/L, IQR 137–139, respectively), whereas GEL increased the Na+ level to 140.5 (IQR 140–141) mmol/L. PL and HES decreased osmolality (277.2 mOsm/kg, IQR 275.7–278.4; and 280.9 mOsm/kg, IQR 279.3–282.0, respectively). GEL increased it to 285.7 (IQR 283.7–286.8) mOsm/kg. All test solutions caused a similar statistically significant (p < 0.05) drop in base excess and bicarbonate concentration, and these fell outside the reference values. Due to its composition, GEL caused a significant increase in lactate concentration. HES and GEL caused a statistically significant drop in strong ion difference value. Due to high lactate level, the effect of GEL was most pronounced.

Conclusions: Balanced intravenous solutions should be safe in terms of their impact on human plasma electrolyte and meta­bolic equilibrium when administered to replace up to 20% of blood volume. In metabolic acidosis, balanced succinylated gelatin should be used with caution. Therefore, arterial blood gas analysis should be performed in patients in whom significant amounts of fluid are administrated, preferably with assessment of Cl–, Na+, lactate concentrations as well as pH, osmolality, and strong ion difference.