Effect of preoperative colon preparation on serum potassium

Although surgeons and anesthesiologists are constantly warned of the danger of hypokalemia following mechanical bowel preparations during the peri- and intraoperative periods, the amount and significance of this problem have not been quantitated. Therefore, the magnitude of the potassium (K+) depletion resulting from three to four days of mechanical bowel preparation was measured in a randomized, prospective fashion in 53 patients. The 27 patients in Group I received intravenous and/or oral potassium chloride supplementation during the preoperative bowel preparation, while the 26 patients in Group II received no supplementation. In an additional five patients, renal and colonic excretory potassium losses were measured to determine if they correlated with preoperative serum potassium levels. All patients had a standard preparation consisting of clear liquid diet (15 mmol K+/day), magnesium citrate orally, enemas, and oral antibiotics. Serum K+ levels in patients in Group I decreased from control levels of 4.01 + 0.41 mmol/1 to 3.71 +/- 0.58 (P less than 0.01) despite an average of 60 mmol potassium chloride supplementation during the preparation. The serum potassium levels in patients in Group II decreased from 4.13 + 0.69 mmol/1 to 3.43 +/- 0.53 (P less than 0.001) during the preparation. Measurement of stool K+ content revealed values that varied considerably between patients and that did not correlate with immediate preoperative serum levels. Urinary K+ measurement showed little renal compensation during the preparation and it did not significantly correlate with preoperative serum levels either.