Correction of Dialysis-Induced Metabolic Alkalosis

Metabolic alkalosis, a disorder that causes elevations in serum bicarbonate and arterial pH, is a common metabolic abnormality found in nearly half of hospitalized patients but is rare in patients with end-stage renal disease (ESRD) on hemodialysis (HD) during the pretreatment state. The problem seems to arise due to a high rate of older patients with multiple comorbidities and malnutrition who are undergoing HD. Metabolic alkalosis is associated with increased morbidity and mortality. In this report, we present a case of metabolic alkalosis, describe an innovative approach to manage metabolic alkalosis in the dialysis population, and review the pathophysiology.

Case Presentation

A 63-year-old female with emphysema, diabetic nephropathy, and ESRD on regular HD for 2 months by a tunneled subclavian vein catheter was admitted with 2 weeks of orthopnea and leg swelling. The review of systems was negative for chest pain, cough, wheeze, or sputum production. She was a former smoker with no alcohol or drug misuse. The patient was taking carvedilol 25 mg daily, furosemide 20 mg twice daily, basal insulin premeal, lisinopril 40 mg daily, pantoprazole 40 mg daily, calcium carbonate 400 mg 3 times daily, ferrous sulphate 325 mg daily, and a vilanterol/tiotropium inhaler once daily. Her dialysate outpatient prescription included sodium 140 mEq/L, potassium 2 mEq/L, calcium 2.5 mEq/L, and bicarbonate 36 mEq/L. Our dialysis unit used NaturaLyte dry pack for bicarbonate dialysis.

The patient appeared tachypneic with 26 respirations/min, oxygen saturation of 89% on room air, which improved to 94% on a 2 L nasal cannula. Her heart rate was 89 beats/min, blood pressure was 129/72 mm Hg, and body mass index was 21.2. The physical examination revealed jugular venous distension, lung crackles, reduced air entry, and pedal edema. Muscle wasting was noted in the arms and thighs. The tunnel catheter did not appear infected.

The patient’s blood work showed sodium, 136 (reference, 132-140) mmol/L; potassium, 4.3 (reference, 3.5-5.0) mmol/L; chloride, 89 (reference, 98-111) mmol/L; total CO₂, 36 (reference, 24-28) mEq/L; blood urea nitrogen, 21 (reference, 7-21) mg/dL; creatinine 3.4 (reference, 0.5-1.4) mg/dL; and albumin, 2.7 (reference, 3.7-5.0) mg/dL. Arterial gases showed pH, 7.56 (reference, 7.35-7.45), partial CO₂, 47 (reference, 35-45) mm Hg; bicarbonate, 42 (reference, 22-26) mEq/L; partial O₂, 54 (reference, 75 to 100) mm Hg. Brain natriuretic peptide was 2,800 (normal, < 100) pg/mL with a normal troponin. X-rays showed pulmonary congestion and bilateral pleural effusions that were transudative on fluid analysis. An echocardiogram showed ejection fraction of 20 to 25% with normal valves (baseline ejection fraction of 60%-65%). A coronary arteriogram revealed severe nonischemic cardiomyopathy.

Treatment

To reduce bicarbonate levels, 3 L of normal saline solution were infused prefilter during HD, and ultrafiltration (UF) of 4.5 L achieved a net UF of -1.5 L over 3.5 hours on lower dialysate bicarbonate (30 mEq/L). Good catheter flow was achieved with a blood flow rate of 350 mL/min and a dialysate flow of 700 mL/min. Venous blood gases and basic serum metabolic panels were obtained throughout the first HD session (Table 1). Improvement in pH from 7.5 to 7.43 and in total CO₂ from 36 to 30 mEq/L were noted after the treatment. Subsequently, we used the same membrane (Optiflux F160NRe) for 2 consecutive daily treatments to remove excess fluid and prevent worsening alkalosis using the same minimal bicarbonate bath, but no further normal saline solution was given.

Outcome

Volume overload was controlled as needed with UF. The bicarbonate did not drop after the second HD session, suggesting low organic acid production in the intradialytic period. By shortening the duration of dialysis to 3 hours and improving nutritional intake, we achieved dry weight, and the patient was discharged home with a total CO₂ of 25 mEq/L. Outpatient dialysis sessions were arranged to run at shorter duration (3 hours compared with 3.5 hours) and use low bicarbonate dialysate. The patient was admitted several times afterward for acute decompensated heart failure, but in all those admissions, her bicarbonate was in the normal-to-high range, between 23 and 30 mEq/L.

Discussion

Metabolic alkalosis is relatively rare in ESRD patients on HD. Particularly in the predialysis period, but with the growing number of older patients undergoing HD and the aggressive treatment of acidosis with relatively higher buffer concentrations; there has been an increase in the incidence of metabolic alkalosis in patients on HD. In the Fresenius Medical Care (FMC) prevalent HD patient study, predialysis bicarbonate levels have increased overtime from a mean (SD)22.9 (3.1) mEq/L in 2004 to a mean (SD) 24.1 (3.5) mEq/L in September 2011, with 25% of patients > 26.0 mEq/L compared with only 6% in 2004.¹ The condition has been associated with cardiac arrhythmia, intradialytic hypocalcemia, hypokalemia, hypercapnia, hypoxia, accelerated hypertension, and seizure.^2-4 Metabolic alkalosis may be associated with increased mortality.^5-7 However, the effect dissipated after adjusting for inflammation and nutritional status.⁶