Nephrology metabolic acidosis in children

Metabolic Acidosis in Children Metabolic acidosis is defined by reduced serum bicarbonate with consequent acidemia, arising from excess acid generation, impaired renal acid excretion, or bicarbonate loss. Classically it is categorized as high-anion gap (AG) or normal-AG (hyperchloremic). Etiologies. High-AG causes include lactic acidosis (sepsis, hypoperfusion, mitochondrial disease), ketoacidosis (diabetes), renal failure, toxin/ingestions (methanol, ethylene glycol, salicylates, metformin), massive rhabdomyolysis, and tumor lysis. Normal-AG causes reflect bicarbonate loss or reduced H+ secretion: diarrhea, enteric fistulae, proximal/distal renal tubular acidosis, early renal failure, and drugs (acetazolamide, aminoglycosides, cisplatin, ifosfamide; heavy metals). Clinical features. Acute cases present with tachypnea or Kussmaul respirations, lethargy, and in severe acidemia hemodynamic instability. Chronic acidosis may be subtle, causing poor growth or rickets. Diagnostics. Obtain ABG/VBG and electrolytes. Calculate the anion gap: AG = Na (Cl + HCO۳) (normal ۴-۱۲ mEq/L); correct downward for hypoalbuminemia (۲.۵ mEq/L drop in AG per ۱ g/dL albumin decrease). For metabolic acidosis, expected respiratory compensation is Winter's formula: PCO۲ ≈ ۱.۵ × HCO۳ + ۸ ± ۲. Unmask mixed disorders with AAG = AG - ۱۲, AHCO۳ = ۲۴ - HCO۳, and A-gap = AAG AHCO۳; a markedly positive A-gap suggests concomitant metabolic alkalosis, whereas a negative A-gap indicates additional hyperchloremic acidosis. Electrolyte shifts are predictable: each ۰.۱ fall in pH raises K+ by ~۰.۶ mEq/L; ionized Ca۲+ and Mg۲+ rise due to reduced protein binding. Management. Treat the cause (insulin and fluids for DKA; fluids/antibiotics for sepsis; antidotes or dialysis for toxins; alkali therapy for RTA). Reserve intravenous sodium bicarbonate for severe acidemia (pH ۷.۰) or impaired renal acid excretion with persistent pH ۷.۲. In emergencies, give ۱ mEq/kg (max ۵۰ mEq) slowly; for replacement, estimate deficit = (target - current HCO۳) × weight × ۰.۴-۰.۵, administer in divided doses with serial gases and electrolytes. Early recognition and targeted therapy prevent complications and improve pediatric outcomes.