FACTORS AFFECTING SERUM AND URINARY POTASSIUM LEVELS IN PATIENTS WHO UNDERGO OPEN HEART SURGERY.

Abstract

The purposes of this research were to: (1) describe selected fluid and electrolyte changes that occur during the first four hours after open heart surgery; (2) determine whether significant hourly changes occurred in: blood pH, fluid intake, exogenous potassum chloride replacement, fluid output, or serum and urinary sodium and potassium levels; and finally, (3) delineate which of the above variables were most strongly related to changes in serum and urinary, sodium and potassium levels. Fifty-three patients who had undergone cardiac surgery involving cardiopulmonary bypass were studied. Urine and blood samples were collected every hour for the first four hours postoperatively and were analyzed for sodium and potassium content using flame photometry. Blood pH and exogenous potassium chloride replacement were recorded from the anesthesiologist's and nurse's records. Fluid intake and fluid output were measured directly by the investigator. Analyses included both descriptive and correlational statistics. In addition, a repeated measures procedure (MANOVA) was performed to discern performance trends over time. The data showed that hypokalemia (defined as a serum potassium level less than 4.0 mEq/L) was present in approximately 52 percent of the subjects for the first two postoperative hours and that by the fourth hour only 15 percent of the subjects were hypokalemic. In addition, subjects were noted to retain 2.47 liters of fluid over the four hour period. Significant differences in fluid output were noted across time. Serum sodium levels did not change significantly across time even though serum potassium levels did. The data indicated that the best predictors of hypokalemia were fluid intake and fluid output. Both of these variables had a significance level of p = .000. Regression analysis showed that fluid intake and exogenous potassium chloride replacement explained 11.9 percent of the variance in serum potassium at a significance level of p = .008. Furthermore, fluid output explained 7.3 percent of the variance in urinary potassium (p = .030).