Renal function and urinary excretion of electrolytes in patients receivingcyclic parenteral nutrition

Background: Long-term parenteral nutrition (LTPN) has been shown to induce renal impairment and hone demineralization. However, the mechanism of both injuries has not been clarified. Methods:: This prospective study was perfo rmed in 16 patients with short bowel syndrome, aged 28 to 63 years, who had received LTPN for 31 +/- 7 months. Urinary excretion of electrolytes were measured before (diurnal, 12 hours) and during (nocturnal, 12 hours) parent eral nutrition. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured in the morning after the nutritional bag supply. Results: Mean GFR was 86 +/- 7 mL/min/1.73 m(2) and ERPF was 412 +/- 31 mL /min/1.73 m(2). Decreased GFR was present in 9 patients. There was no relat ion between renal function and age or the duration of LTPN. Urine volume an d excretion of urea, creatinine, sodium, magnesium, and phosphate but not p otassium increased significantly in nocturnal urine compared with diurnal u rine. On the basis on 24-hour calciuria, 7 patients were normocalciuric (NC a) whereas 9 were hypercalciuric (HCa). Both had excessive nocturnal calciu ria, but only the HCa group had diurnal hypercalciuria, the calcium supply being identical. Bone mineral density (BMD) was slightly, although not sign ificantly, higher in NCa group, but in all patients BMD correlated signific antly with calciuria. Serum parathyroid hormone and vitamin D were not diff erent in the two groups. Conclusions: In patients receiving LTPN, renal fun ction is frequently impaired, by a mechanism which remains unclear. In noct urnal cyclic mode of nutrition, urinary volume and electrolyte excretion oc curred predominantly during the infusion, but some patients have diurnal hy percalciuria. In these patients a defect in renal calcium reabsorption or m ore likely the inability of Lune to retain the infused calcium may be respo nsible for bone demineralization.