Hyperchloraemic metabolic acidosis with hypokalaemia and osteomalacia
Daphne S-L Gardner & Daniel E Flanagan
Background: A 52-y-old lady (Mrs M) presented with a 10-day history of progressive generalised weakness, dysarthria and un-coordination. 26 y ago, she had cervical carcinoma, requiring a hysterectomy, oophorectomy and radiotherapy. This led to a vesicovaginal fistula, requiring a cystectomy and ureterosigmoidostomy. She is known to have osteoporosis. Medications: calfovit D3 one/d (started 5 days prior to admission), risedronate, lansoprazole. She had HRT until 50 y. Examination: Mrs M was in extremis, with profound tachypnoea, confusion and drowsiness (GCS12/15). FVC was reduced (1.6L). Power was generally reduced throughout (grade 34/5). Investigations: ABG showed profound metabolic acidosis: pH 7.13, pO2 20.1 kPa, pCO2 1.62 kPa, base excess −24.2. Serum biochemistry: Sodium(Na+) 145 mmol/l (134144), Potassium(K+) 3.4 mmol/l (3.55.1), Bicarbonate(HCO31−) 4 mmol/l (2331), Urea 14.2 mmol/l (2.87.6), Creatinine(Cr) 108 μmol/l (5596), Chloride 125 mmol/l (98107), Calcium(Ca2+) 1.92 mol/l (2.122.55), Phosphate (PO43−) 0.38 mmol/l (0.81.4), Magnesium 0.57 mmol/l (0.71.0). PTH was raised [136 ng/l (1565)], 25-OHD level was low-normal [11.5 μg/l (740)]. Management: Mrs M went to the intensive care unit, was intubated and given intravenous NaHCO3, PO43−, Ca2+ and K+. Despite 120 mmol/d of K+, this remained low (3.0). She was extubated on day 2. By day 4, metabolic derangements were normalising and she was started on oral calcichew and NaHCO3. By day 6, she felt sufficiently well and self-discharged. Electrolytes on discharge: Na+147, K+4.2, HCO31− 19, Urea 5.3, Cr 86, Ca2+2.06, PO43− 0.78.
Discussion: Ureterosigmoidostomies often result in chronic hyperchloraemic metabolic acidosis. Unusually, this patient presented years later, acutely unwell, with generalised weakness, hypokalaemia and osteomalacia. It is unclear what triggered this. Colonic K+ reabsorption is poor and together with chronic acidosis, leads to reduced total body K+. Chronic acidosis also increases urinary Ca2+ and PO43− loss, leading to osteomalacia. It is important these patients are maintained on oral sodium bicarbonate to prevent such complications.