Isotonic saline in elderly men: an open-labelled controlled infusion study of electrolyte balance, urine flow and kidney function.

Isotonic saline is a widely-used infusion fluid, although the associated chloride load may cause metabolic acidosis and impair kidney function in young, healthy volunteers. We wished to examine whether these effects also occurred in the elderly, and conducted a crossover study in 13 men with a mean age of 73 years (range 66-84), who each received intravenous infusions of 1.5 l of Ringer's acetate and of isotonic saline. Isotonic saline induced mild changes in plasma sodium (mean +1.5 mmol.l(-1) ), plasma chloride (+3 mmol.l(-1) ) and standard bicarbonate (-2 mmol.l(-1) ). Three hours after starting the infusions, 68% of the Ringer's acetate and 30% of the infused saline had been excreted (p < 0.01). The glomerular filtration rate increased in response to both fluids, but more after the Ringer's acetate (p < 0.03). Pre-infusion fluid retention, as evidenced by high urinary osmolality (> 700 mOsmol.kg(-1) ) and/or creatinine (> 7 mmol.l(-1) ), was a strong factor governing the responses to both fluid loads.