8) Normally, when blood is drawn and allowed to clot before centrifugation, enough potassium is released from platelets to raise the serum level by approximately 0.5 mEq/L. This is accounted for within the limits of the normal range. Excessive errors could occur, however, in the presence of marked leukocytosis or thrombocytosis. These conditions are referred to as pseudohyperkalemia. This can be confirmed by remeasuring serum potassium in a blood sample collected in a heparinized sample tube.3
EKG of patient with more advanced hyperkalemia.
9) Oral sodium phosphate is a cathartic used in bowel preparation prior to colonoscopy. This agent has been associated with changes in serum electrolyte levels that are generally within the normal range but could occasionally cause serious electrolyte disturbances. Significant hypokalemia could develop, particularly in the elderly, and is due to intestinal potassium loss.4
Other abnormalities reported include hyperphosphatemia, hypocalcemia, and hypernatremia. In addition to increased age, risk factors for these disturbances include the presence of bowel obstruction, poor gut motility, and unrecognized renal disease. Additionally, phosphate nephropathy has been well reported after administration of sodium phosphate and might cause irreversible kidney disease with histology resembling nephrocalcinosis.5
10) The most commonly used cation-exchange resin, sodium polystyrene sulfonate, is frequently used to manage hyperkalemia in patients with chronic kidney disease. Use of this resin could result in hypokalemia, hypomagnesemia, and—occasionally—metabolic alkalosis. After the oral administration of this drug, sodium is released from the resin in exchange for hydrogen in the gastric juice. As the resin passes through the rest of the gastrointestinal tract, the hydrogen is then exchanged for other cations, including potassium, which is present in greater quantities, particularly in the distal gut. Potassium binding to the resin is influenced by duration of exposure, which is primarily determined by gut transit time.
The primary potential complication of using sodium polystyrene sulfonate is the development of sodium overload. The absorption of sodium from the resin by the gut might lead to heart failure, hypertension, and occasionally hypernatremia. Because the resin binds other divalent cations, hypocalcemia and hypomagnesemia could also develop. Decreased plasma levels of magnesium and calcium are more likely to occur in patients taking diuretics or in those with poor nutrition.6 Use of the resin could also lead to metabolic alkalosis when administered with antacids or phosphate binders such as magnesium hydroxide or calcium carbonate. As magnesium and calcium bind to the resin, the base is then free to be absorbed into the systemic circulation. TH
Dr. Casey works in the Department of Internal Medicine, Section of Hospital Internal Medicine, Division of Nephrology and Hypertension at the Mayo Clinic, Rochester, Minn.
References
- Liou HH, Chiang SS, Wu SC, et al. Hypokalemic effects of intravenous infusion or nebulization of salbutamol in patients with chronic renal failure: comparative study. Am J Kidney Dis. 1994 Feb;23(2):266-271.
- Martinez-Vea A, Bardaji A, Garcia C, et al. Severe hyperkalemia with minimal electrocardiographic manifestations: a report of seven cases. J Electrocardiol. 1999 Jan;32(1):45-49.
- Stankovic AK, Smith S. Elevated serum potassium values: the role of preanalytic variables. Am J Clin Pathol. 2004 Jun;121 Suppl:S105–S112.
- Beloosesky Y, Grinblat J, Weiss A, et al. Electrolyte disorders following oral sodium phosphate administration for bowel cleansing in elderly patients. Arch Intern Med. 2003 Apr 14;163(7):803–808.
- Curran MP, Plosker GL. Oral sodium phosphate solution: a review of its use as a colorectal cleanser. Drugs. 2004;64(15):1697-1714.
- Chen CC, Chen CA, Chau T, et al. Hypokalaemia and hypomagnesaemia in an oedematous diabetic patient with advanced renal failure. Nephrol Dial Transplant. 2005 Oct;20(10):2271-2273.