Changes in the electrolyte content of serum and urine during total parenteral nutrition

Phosphate metabolism in the red cell of sick prematures

The effect of different amounts of phosphorus supplementation on phosphate metabolism was studied in two groups of sick preterms (B and C) during the first week of life. Group B included prematures that started formula milk feeding from day 3 and group C neonates on total parenteral nutrition with phosphate supplementation for 7 days. Twelve healthy preterm neonates on formula milk feeding from day 2 (group A) were used as controls. On the 7th day of life all phosphate parameters measured in group C (plasma and red cell inorganic phosphate and erythrocyte ATP and 2,3-diphosphoglycerate) were found significantly lower than in the controls (1.60 +/- 0.07; 0.60 +/- 0.08; 1.45 +/- 0.09 and 4.42 +/- 0.18 vs. 2.05 +/- 0.10; 0.94 +/- 0.11; 1.69 +/- 0.07 and 6.24 +/- 0.42 mmol/l, respectively). The renal tubular reabsorption of phosphate was also lower in this group (86.8 +/- 3.2 vs. 97.3 +/- 1.0%). No significant differences were observed between groups B and A. Higher phosphorus intake that was better achieved through early milk feeding prevented phosphate depletion and the decline of 2,3-diphosphoglycerate in the erythrocytes even of sick neonates which in turn might help to improve tissue oxygenation. The amount of parenteral phosphate supplementation that could have beneficial effects on red cell phosphate parameters needs further investigation.

Renal and electrolyte effects of total parenteral nutrition

Effects of short-term (4-14 days) total parenteral nutrition on renal handling of water and electrolytes were studied retrospectively in 24 patients and prospectively in eight patients. There was 33% incidence of hyponatremia and significant reductions in serum creatinine (from 1.03 +/- 0.06 to 0.88 +/- 0.06 mg/dl, p less than 0.001), phosphorus (from 3.2 +/- 0.14 to 2.5 +/- 0.17 mg/dl, p less than 0.005) and uric acid (from 6.09 +/- 0.38 to 3.66 +/- 0.24 mg/dl, p less than 0.001) were observed. Hypouricemia correlated with increased fractional excretion of urate (r = 0.81, p less than 0.05). Hypophosphatemia was associated with increased tubular reabsorption of phosphate. Clearance studies in eight patients showed high urine flow rate (1.7 +/- 0.2 ml/min), osmolar clearance (3.2 +/- 0.7 ml/min), urinary nonelectrolyte, nonurea solute excretion (0.23 +/- 0.14 mmol/min), and negative free water clearance (TcH2O = 1.5 +/- 0.6 ml/min). These data suggest presence of compartmental shifts, expanded extracellular fluid volume, and possible direct effects on renal tubular transport functions during total parenteral nutrition.