The effect of intravenous lactated Ringer's solution versus 0.9% sodium chloride solution on serum osmolality in human volunteers

Animal studies have shown that large volumes of IV lactated Ringer's soluti on (LR) decrease serum osmolality, thereby increasing cerebral water. These studies have led to recommendations to limit LR to avoid cerebral edema in neurosurgical patients. Eighteen healthy human volunteers aged 20-48 yr re ceived 50 mL/kg LR over 1 h on one occasion and 0.9% sodium chloride (NS) o n another. Venous samples were taken at baseline (T1), at infusion end (T2) , and 1 h after T2 (T3). Time until first urination was noted. With LR, ser um osmolality decreased by 4 +/- 3 mOsm/kg from T1 to T2 and increased insi gnificantly with NS. At T3, osmolality returned almost to baseline in the L R group. Blood pH increased from T1 to T2 with LR by 0.04 +/- 0.04 and decr eased with NS by 0.04 0.04. These pH changes persisted at T3. Subjective me ntal changes occurred only with NS. Abdominal discomfort was more common wi th NS. Time until first urination was longer with NS (106 +/- 11 min) than with LR (75 +/- 10 min) (P < 0.001). Ln healthy humans, an infusion of larg e volumes of LR, but not NS, transiently decreased serum osmolality, wherea s acidosis associated with NS persisted and urinary output was slower with NS. Implications: Large volumes of lactated Ringer's solution administered to healthy humans produced small transient changes in serum osmolality. Lar ge volumes of sodium chloride did not change osmolality but resulted in low er pH.