Acute Renal Failure with Bowel Preparation: A Serious Problem Lurking in the Geriatric Population

Smitha Battula, MD, and Catherine M. Fleisher, MD, Aultman Hospital,Canton Medical Education Foundation, Stark County Medical Group, Ohio

Published Online: July 11, 2007 - 11:19:30 AM (CDT)

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The case of bowel preparation for screening colonoscopy in the geriatric population is an important issue of increasing urgency. Oral sodium phosphate solution (Fleet Phospho-soda) is an osmotic cathartic used for bowel preparation in patients undergoing colonoscopy. Its low cost, the small volume required to consume, and similar efficacy make sodium phosphate solution the preferred choice compared with polyethylene glycol-electrolyte lavage solution.¹ Nevertheless, the many contraindications for sodium phosphate must be carefully considered before prescribing this bowel preparation. If used inappropriately, it can lead to life-threatening complications, such as hyperphosphatemia or acute renal injury, especially in the geriatric population. With the increasingly aging American population, and with current guidelines of preventive medicine, a greater degree of prudence is required when choosing a colon preparation agent.

Case Presentation

A 75-year-old woman presented to the office with symptoms of dry mouth and weakness 3 days after undergoing an elective screening colonoscopy. She reported 3 days of profuse diarrhea that began after consuming 4 fl oz of oral sodium phosphate solution for bowel preparation. Her medical history included hypertension, chronic obstructive pulmonary disease, atherosclerosis, hypothyroidism, and peripheral vascular disease. The patient continued taking her antihypertensive medications (hydrochlorothiazide and valsartan) during pre? and post?colon cleansing with sodium phosphate. She was not eating or drinking but had no complaints of nausea or vomiting.

Physical examination revealed dry mucous membranes and skin tenting. The patient was hemodynamically stable, but the laboratory test results showed a serum creatinine level of 6.6 mg/dL. She was immediately transferred to the hospital.

Repeat tests taken at the hospital revealed: sodium, 123 mmol/L (normal, 136-148 mmol/L); chloride, 87 mmol/L (96-110 mmol/L); blood urea nitrogen, 55 mg/dL (7-26 mg/dL); creatinine, 8.4 mg/dL (0.6-1.5 mg/dL); calcium, 7.1 mg/dL (8.5-10.5 mg/dL), with ionized fraction of 0.94 mmol/L (1.16-1.32 mmol/L); phosphorus, 9.9 mg/dL (2.5-4.9 mg/dL). Brain natriuretic peptide and cardiac enzyme levels were normal.

Urinalysis showed mild proteinuria (30 mg/dL), with occasional granular casts. Spot urine electrolyte testing showed: sodium, 55 mmol/L; chloride, 47 mmol/L; creatinine, 43.7 mg/dL; urine osmolality, 198 mOsm/kg H₂O. Renal ultrasound and magnetic resonance imaging showed the kidneys and renal arteries were normal, with no evidence of hydronephrosis or obstruction. Echogenicity, however, was consistent with renal disease.

Her medications were temporarily discontinued, and she was treated with intravenous fluids and hemodialysis on hospital day 1. Renal function and serum phosphorus levels improved gradually (Figure). The patient is currently off dialysis and is back to her state of health before colonoscopy.

Figure?Postcolonoscopy changes in serum creatinine and phosphorus levels, hospital days 1 to 23.

Discussion

Oral sodium phosphate solution is an osmotic cathartic that has emerged as a preferred colon-cleansing agent for patients undergoing colonoscopy and is cheaper than polyethylene glycol-electrolyte lavage solution.¹ Oral sodium phosphate solution contains 2.4 g of monobasic sodium phosphate and 0.9 g of dibasic sodium phosphate.

Several head-to-head studies that compared the 2 solutions demonstrated comparable efficacy and similar side-effect profiles.^2-6 However, an increased incidence of intravascular volume depletion and electrolyte imbalance was noted in groups taking oral sodium phosphate.⁷ Hypovolemia with transient hyperphosphatemia after sodium phosphate administration presents an increased load of phosphorus and calcium to the distal tubule. This leads to calcium phosphate formation and deposition, causing acute renal failure. Life-threatening complications of hyperphosphatemia, acute phosphate nephropathy, and acute nephrocalcinosis, as well as death after use of oral sodium phosphate solution, have been reported.^7-10 In one study, renal biopsy specimens revealed diffuse tubular injury, with abundant calcium phosphate deposition in distal tubules and collecting ducts.⁷

Acute renal failure associated with severe hyperphosphatemia and hypocalcemia may develop within days after consumption of sodium phosphate.¹¹ Alternatively, renal failure can be an incidental finding weeks after sodium phosphate use, without the signs of an acute syndrome. Such patients present with mild symptoms and no serum calcium or phosphate level abnormalities.¹¹ Physicians should also be aware that acute phosphate nephropathy may lead to long-term renal dysfunction. In one study, 17 of 21 patients who had acute renal failure after sodium phosphate use developed chronic renal insufficiency.¹⁰

Contraindications for oral sodium phosphate solution include^7,10:

• Very advanced age
• Congestive heart failure
• Impaired renal function
• Intestinal obstruction
• Decreased intestinal motility and/or increased permeability
• Liver cirrhosis
• Inadequate hydration
• Hypertension with concurrent use of a diuretic, an angiotensin-converting-enzyme inhibitor, or an angiotensin receptor blocker.

Appropriate interventions, such as maintaining fluid balance (with hydration) and watching for concurrent medications, are required to prevent life-threatening complications.

Conclusion

With current guidelines and the strict recommendations for preventive medicine, a great degree of prudence is required in the selection of a colon preparation agent. Physicians should become familiar with the many contraindications for oral sodium phosphate solution. Patients should be thoroughly educated about maintaining a positive fluid balance, medication use, and possible complications.

References

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2. Poon CM, Lee DW, Mak SK, et al. Two liters of polyethylene glycolelectrolyte lavage solution versus sodium phosphate as bowel cleansing regimen for colonoscopy: a prospective randomized controlled trial. Endoscopy. 2002;34:560-563.
3. Huppertz-Hauss G, Bretthauer M, Sauar J, et al. Polyethylene glycol versus sodium phosphate in bowel cleansing for colonoscopy: a randomized trial. Endoscopy. 2005;37:537-541.
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