Total body potassium in surgical patients.

Abstract

The efficacy of parenteral nutrition was evaluated by quantitating the body cell mass and its supporting extracellular environment by measuring total exchangeable sodium (Na,), total body water (TBW), and total exchangeable potassium (K,). The TBW and Na, were measured by isotope dilution by using tritiated water and sodium-22, respectively. Total exchangeable potassium was determined indirectly using the formula: K, = R x (TBW) - Na8, where R is the ratio of the sum of sodium plus potassium content to the water content in a whole blood sample. The indirect measurement of K, was validated by simultaneously determining K, indirectly and directly, by K-42 dilution, in 15 normal, five uremic, and 14 dogs rendered hypo-osmolar by intramuscular Pitressin and a water load. The correlation between the two measurements of K, was excellent with a correlation coefficient of 0.98. Similarly, the simultaneous determination of K, both indirectly and by K-42 dilution in 20 patients with a variety of illnesses resulted in a mean difference of -0.7 percent and a correlation coefficient of 0.99. The experimental data thus validates the indirect measurement of K,. TBW, Na,, and K, were simultaneously determined in four groups of surgical patients; 13 normal patients, eight with longstanding sepsis, five with starvation, and six with chronic sepsis who, in addition, received intravenous hyperalimentation. K, expressed as a function of TBW was reduced in the patients with sepsis and starvation, but normal in similar patients receiving parenteral hyperalimentation. The reverse was observed in the Na,, expressed as a function of TBW, which was elevated in the septic and starved patients, but normal in patients receiving intravenous hyperalimentation.