Table 6.

Recommended degrees of fluid restriction on the basis of the urine to plasma electrolyte ratio

(UNa+UK)/PNaInsensible Water Losses (ml)Water Loss beyond Insensible Losses (ml)Recommended Fluid Restriction (ml)
>18000–800a0
0.5–1800300–800≤500
<0.5800300–800≤1000
  • These estimates assume a urine volume of 1 L and a fluid intake closer to the maximal amount allowed by fluid restriction. UNa, urine sodium concentration; UK, urine potassium concentration; PNa, plasma sodium concentration. Modified from reference 35, with permission.

  • a Patients actually could have a negative net water loss (i.e., free water retention) if the urine to plasma ratio is significantly high.