Infant With Hypokalemic Alkalosis and Nephrocalcinosis
A 10-month-old girl is admitted with 3 days of vomiting and lethargy. Weight is 7.2 kg (0.3rd percentile), length 68 cm (10th percentile). She has been polyuric since birth and prefers salty foods. BP is 82/50 mmHg, pulse 150/min, and capillary refill 4 s. Venous pH is 7.50, bicarbonate 32 mmol/L, potassium 2.4 mmol/L, sodium 130 mmol/L, chloride 84 mmol/L, and creatinine 0.3 mg/dL. Urine sodium is 40 mmol/L, potassium 25 mmol/L, and chloride 58 mmol/L; urine calcium-to-creatinine ratio is 0.8 mg/mg (normal <0.2). Ultrasound shows bilateral medullary nephrocalcinosis. Serum renin and aldosterone are elevated.
1. Identify the likely tubular disorder and explain how the urine chloride, blood pressure, and nephrocalcinosis fit; include one alternative you would exclude and how.
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Likely diagnosis. Classic Bartter syndrome, a salt-wasting tubulopathy. The hypokalemic, hypochloremic metabolic alkalosis with elevated urine chloride (58 mmol/L) indicates renal chloride wasting rather than gastric loss. Vomiting from pyloric stenosis typically produces low urine chloride (<20 mmol/L) because the kidney conserves chloride. Her normal-to-low blood pressure, polyuria, salt craving, hypercalciuria (urine calcium/creatinine 0.8), and medullary nephrocalcinosis fit Bartter syndrome. Elevated renin and aldosterone are secondary to volume depletion.
Alternative to exclude. Loop or thiazide diuretic exposure can mimic Bartter or Gitelman syndrome. Obtain a urine diuretic screen and a careful medication history. Gitelman syndrome is less likely at this age and usually causes hypocalciuria rather than nephrocalcinosis.
Reasoning. The combination of high urine chloride, low blood pressure, and nephrocalcinosis points away from extrarenal losses and toward a renal tubular salt leak. Genetic testing can later define the subtype, but it is not needed before initial treatment.
2. Outline initial fluid and electrolyte resuscitation, including how fast to correct sodium and potassium and what complications you monitor.
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Resuscitation. She has shock (capillary refill 4 s, tachycardia). Give 10–20 mL/kg isotonic crystalloid (0.9% saline) in aliquots, reassessing perfusion, lungs, and urine output. Avoid potassium-containing boluses. After stabilization, replace ongoing salt and water losses; Bartter patients often need 1.5–2 times maintenance fluids and generous sodium chloride.
Potassium. Replace potassium cautiously with oral or intravenous chloride salt. In severe hypokalemia with weakness, use a monitored intravenous infusion, generally not faster than 0.5–1 mEq/kg/hour through a central line or with cardiac monitoring; peripheral fluids should not exceed 40 mEq/L. Check magnesium and replace if low.
Sodium. Correct chronic hyponatremia slowly-no more than 8–10 mmol/L in 24 hours-to avoid osmotic demyelination. Monitor electrolytes every 4–6 hours initially, ECG for arrhythmia, urine output, and neurological status. Treat vomiting and dehydration, but do not stop salt replacement abruptly. Once stable, transition to oral potassium and salt, and involve nephrology for long-term prostaglandin inhibition.
3. Describe the long-term plan, including the role and risks of indomethacin, potassium supplementation, and surveillance for growth and nephrocalcinosis.
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Indomethacin. Nonsteroidal anti-inflammatory drugs reduce renal prostaglandin synthesis, decreasing salt and water wasting and polyuria in Bartter syndrome. They do not correct the underlying defect and can cause gastritis, reduced GFR, hypertension, and electrolyte disturbance. Use the lowest effective dose, with food or a proton-pump inhibitor if needed, and monitor creatinine, urine output, blood pressure, and growth.
Potassium and salt. Continue oral potassium chloride and sodium supplements, adjusting to serum potassium and growth. A high-salt diet and free access to water are important. Monitor magnesium and calcium.
Nephrocalcinosis. Hypercalciuria may persist; periodic renal ultrasound and urine calcium-to-creatinine ratio are reasonable. Nephrocalcinosis may not resolve, so the goal is preventing progression and CKD.
Genetics and referral. Refer to pediatric nephrology and genetics for subtype confirmation, family counseling, and surveillance for hearing loss (BSND) or other features. Growth should be plotted at every visit; poor growth despite therapy suggests inadequate electrolyte replacement or NSAID toxicity.