Background: Oral sodium phosphate is currently used for colon
preparation before colonoscopy or barium enema. Sodium phosphate induces
hyperphosphatemia, hypocalcemia, and hypokalemia. Elderly patients are at an
increased risk for phosphate intoxication because of decreased glomerular
filtration rate, medication use, and systemic and gastrointestinal diseases.
We investigated these electrolyte disorders and their correlation with
creatinine clearance, coexistent diseases, medications, and functional status.
Methods: Thirty-six hospitalized patients were included in the study.
On day 1, patients were administered 2 doses of oral sodium phosphate. Venous
blood samples for electrolyte determination were obtained at 7 am
on days 1, 2 (the procedure day), and 3. Urine samples were obtained from 10
patients. Results: An increase in serum phosphorus level was
correlated with a decreased creatinine clearance (R = -0.52;
p = .001). Hypocalcemia and hypokalemia were present in 21 (58%) and
20 (56%) patients, respectively. Patients with a serum potassium concentration
of 3.5 mEq/L or less on day 2 had a lower serum potassium concentration on day
1 vs those with a serum potassium concentration >3.5 mEq/L on day
2 (p = .03). Five (dependent patients) had a serum potassium
concentration of 3 mEq/L or less, and 2 had severe diarrhea, necessitating
treatment. There were more demented patients with hypokalemia compared with
normokalemic patients (p < .05). Urinary fractional excretion of
phosphorus tripled on day 2 (p = .01). Potassium and sodium
fractional excretion remained unchanged. Conclusions: Sodium
phosphate induces serious electrolyte abnormalities in the elderly. The
frequency and severity of hypokalemia is due to intestinal potassium loss
associated with inadequate renal potassium conservation and is apparently more
prevalent in frail patients. Assessment of serum electrolytes, phosphorus, and
calcium before sodium phosphate preparation is advised, and in selected
patients, postprocedural assessment and correction may be required.
