A comparison of renal phosphorus regulation in thermally injured and multiple trauma patients receiving specialized nutrition support

To compare phosphorus intake and renal phosphorus regulation between therma lly injured patients and multiple trauma patients, 40 consecutive criticall y ill patients, 20 with thermal injury and 20 with multiple trauma, who req uired enteral tube feeding were evaluated. Phosphorus intakes were recorded for 14 days from the initiation of tube feeding which was started 1 to 3 d ays postinjury. Serum for determination of phosphorus concentrations was co llected at days 1, 3, 7, and 14 of the study period. A 24-hour urine collec tion was obtained during the first and second weeks of nutrition support fo r urinary phosphorus excretion, fractional excretion of phosphorus, renal t hreshold phosphate concentration, and phosphorus clearance. Average total d aily phosphorus intake during the 14-day study for thermally injured patien ts and multiple trauma patients was 0.99 0.26 mmol/kg/d vs 0.58 +/- 0.21 mm ol/kg/d, respectively, p < .001. Serum phosphorus concentration on the thir d day of observation was significantly lower in the thermally injured group than those with multiple trauma (1.9 +/- 0.8 mg/dL vs 3.0 +/- 0.8 mg/dL, p less than or equal to .01). A trend toward hypophosphatemia in the thermal ly injured group persisted by the seventh day of feeding (2.7 +/- 1.2 mg/dL vs 3.3 +/- 0.6 mg/dL, p less than or equal to .04). Differences in urinary phosphorus excretion was not statistically significant between the thermal ly injured and multiple trauma groups (271 +/- 213 mg/d vs 171 +/- 181 mg/d for week 1, and 320 +/- 289 mg/d vs 258 +/- 184 mg/d for week 2, respectiv ely). Urinary phosphorus clearance, fractional excretion of phosphorus, or renal threshold phosphate concentrations were also not significantly differ ent between thermally injured and multiple trauma patients. During nutritio n support, serum phosphorus concentrations are lower in thermally injured p atients compared with multiple trauma patients despite receiving a signific antly greater intake of phosphorus. Renal phosphorus regulation does not si gnificantly contribute to the profound hypophosphatemia observed in thermal ly injured patients when compared with multiple trauma patients during nutr ition support.