Abstract: PUB245
Fluid Restriction in Hyponatremia
Session Information
Category: Fluid, Electrolytes, and Acid-Base Disorders
- 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical
Authors
- Pham, Phuong-Chi T., UCLA Medical Center Olive View, Sylmar, California, United States
- Pham, P.M. T., VA Greater Los Angeles Healthcare System, Los Angeles, California, United States
- Pham, Phuong-Thu T., Ronald Reagan UCLA Medical Center, Los Angeles, California, United States
Introduction
Fluid restriction (advised as fluid intake of 500 mL below average daily urine output, Hyponatremia Expert Panel 2007) to correct hyponatremia for euvolemic/hypervolemic hyponatremia is often minimally effective or ineffective. We present a case illustrating how failure of fluid restriction can be mathematically predicted.
Case Description
A 48-year-old male with non-ischemic heart failure with ejection fraction of 30%, presents for volume overload. Nephrology is consulted for persistent hyponatremia ranging from 122-126 mmol/L despite fluid restriction in the setting of loop diuretic use. On the day of consult, serum sodium (SNa) is 126 mmol/L. Chart review reveals daily fluid restriction of 1.8L/d with urine output averages 4L/d. Urine studies: sodium 66-95 (average 80.5) mmol/L, potassium 35-39 (average 37) mmol/L.
Urine electrolyte free water clearance (EFWC) = Urine volume*(1-[urine Na + urine K]/serum Na) = 4*(1-(80.5+37)/126)=0.3L/d.
Fluid "restriction" of 1.8L/d, albeit much less than urine output of 4L/d, exceeds daily EFWC of 0.3L/d. Fluid intake greater than EFWC cannot correct hyponatremia.
Discussion
As illustrated, fluid restriction to a volume below urine output in this case (i.e., 1.8L << 4L/d) exceeds the daily EFWC (i.e., 1.8L/d fluid intake > 0.3L/d electrolyte-free water lost in urine) and can never correct SNa. The suggestion to reduce fluid intake to 500 mL less than average daily urine output should be revised to be lower than daily EFWC. Alternatively, fluid restriction may be suggested to be [Urine output - (x × TBW + U(Na + K)) ÷ (SNa0 + x)], where x is the change in SNa desired. A negative value predicts that fluid restriction is ineffective. See figure for equation derivation and definitions of terms.
Alternatively, for stable patients with euvolemic hyponatremia who are at goal SNa, advice to not exceed a predicted fluid intake volume may be given. In this case, x is set at zero. The fluid intake volume that would not worsen hyponatremia is [Urine output - (U(Na + K)) ÷ (SNa0)].