Cellular potassium depletion predisposes to hypokalaemia after oral sodiumphosphate

Background: Oral sodium phosphate has become an attractive alternative to p olyethylene glycol for colonic cleansing preparatory to elective colorectal surgery. Its use, however, has been associated with hypokalaemia. The auth ors of the present study tested the hypothesis that patients with cellular depletion of potassium are at significant risk for hypokalaemia with oral s odium phosphate bowel preparation. Methods: In 23 patients, total body potassium was measured by whole-body co unting and intracellular water volume was measured by bioimpedance analysis before oral sodium phosphate bowel preparation. Patients were divided into those whose serum potassium fell to 3.5 mmol/L or lower (Group 1) and thos e whose did not after sodium phosphate treatment (Group 2). Results: The fall in serum potassium concentration over the period of oral sodium phosphate administration was significantly negatively correlated wit h intracellular potassium concentration measured prior to administration (r = - 0.65, P = 0.0009). In Group 1, serum potassium concentration fell from 4.1 +/- 0.1 (standard error of the mean (SEM)) mmol/L to 3.2 +/- 0.1 mmol/ L (P < 0.0001) while in Group 2 there was no significant change in this con centration (4.0 +/- 0.1 vs 3.9 +/- 0.1 mmol/L) as a result of sodium phosph ate treatment. Intracellular potassium concentration prior to administratio n of sodium phosphate was significantly lower in Group 1 (117 +/- 9 mmol/L vs 143 +/- 7 mmol/L, P < 0.05). Conclusions: Caution should be exercised when treating patients with oral s odium phosphate who are considered to be cellularly depleted of potassium. These patients are at risk of hypokalaemia after this treatment.