Fluids in the postoperative period: effects of lack of adjustment to body weight.

OBJECTIVE To compare the differences in fluid and electrolyte balance in patients with low and high weight in the first postoperative day. METHODS Over a period of 18 months, we prospectively evaluated 150 patients in the first 24 hours after surgery, in a university-affiliated hospital intensive care unit. Patients with low weight (< 60 kg) and high body weight (> 90 Kg) were compared in terms of fluid intake and output. RESULTS No significant differences were observed in the volume (4334 ± 1097 vs. 4644 ± 1957 ml/24 h) and composition of the fluids administered (481 ± 187 vs. 586 ± 288 mEq [Na+]administered/24 h). The 24 h urine output was similar (2474 ± 1597 vs.2208 ± 678 ml/24 h) but low weight group showed higher electrolyte elimination (296 ± 195 vs.192 ± 117 mEq [Na+]urine /24 h, p = 0.0246). When the administered fluids were adjusted for body weight, the volume and amount of electrolytes of fluids administered were higher in the low weight group (79 ± 21 vs. 47 ± 22 ml/kg/24 h, p < 0.0001 and 8.8 ± 3.4 vs. 5.8 ± 3.3 mEq [Na+]administered/kg/24 h, p = 0.017, respectively). This group also showed higher urine output and electrolyte elimination (45 ± 28 vs. 22 ± 7 ml/kg/24 h, p = 0.0002 and 5.3 ± 3.5 vs. 1.8 ± 1.2 mEq [Na+]urine/kg/24 h, p < 0.0001, respectively). CONCLUSIONS The lack of adjustment of the fluid therapy to body weight determined that low weight patients received more fluid than high weight patients according to their body weight. This fluid overload could be compensated by increased urine output and electrolyte elimination.