Total body potassium in surgical patients

The efficacy of parenteral nutrition was evaluated by quantitating the body cell mass and its supporting extracellular environment by measuring total exchangeable sodium (Na_e), total body water (TBW), and total exchangeable potassium (K_e). The TBW and Na_e were measured by isotope dilution by using tritiated water and sodium-22, respectively. Total exchangeable potassium was determined indirectly using the formula: K_e = R × (TBW) - Na_e, 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_e was validated by simultaneously determining K_e 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_e was excellent with a correlation coefficient of 0.98. Similarly, the simultaneous determination of K_e 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_e. TBW, Na_e, and K_e 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_e 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_e, expressed as a function of TBW, which was elevated in the septic and starved patients, but normal in patients receiving intravenous hyperalimentation.