Prevention of Hyponatremia during Maintenance Intravenous Fluid Administration: A Prospective Randomized Study of Fluid Type versus Fluid Rate

Objectives To determine the importance of sodium content versus administration rate of intravenous fluids in the development of hyponatremia in postoperative children. Study design In this prospective, randomized, nonblinded study, 124 children admitted for surgery received 0.9% (NS) or 0.45% (N/2) saline solution at 100% or 50% maintenance rates. Plasma electrolytes, osmolality, and ADH at induction of anesthesia were compared with values 8 hours (T8 ), and 24 hours (T24 ; n = 67) after surgery. Blood glucose and ketones were measured every 4 hours. Electrolytes and osmolality were measured in urine samples. Results Plasma sodium concentrations fell in both N/2 groups at T8 (100%: −1.5 ± 2.3mmol/L 50%: −1.9 ± 2.0mmol/L; P < .01) with hyponatremia more common than in the NS groups at T8 (30% vs 10%; P = .02) but not T24 . Median plasma antidiuretic hormone concentrations increased 2- to 4-fold during surgery ( P ≤ .001) and only reattained levels at induction of anesthesia by T24 in the N/2 100% group. On multiple linear regression analysis, fluid type, not rate determined risk of hyponatremia ( P < .04). Two children on 100% developed SIADH (1NS). Fourteen (23%; 7NS) on 50% maintenance were assessed as dehydrated. Dextrose content was increased in 18 for hypoglycemia or ketosis. Conclusions The risk of hyponatremia was decreased by isotonic saline solution but not fluid restriction.