How should I evaluate and manage an ICU child with an unexplained metabolic acidosis?

Evaluation and Management of Unexplained Metabolic Acidosis in ICU Children

Treat the underlying cause first—bicarbonate is reserved only for severe acidosis (pH <7.2, base deficit >10 mmol/L, bicarbonate <12 mmol/L) after ensuring adequate ventilation, and only after addressing the precipitating etiology. 1

Initial Stabilization and Assessment

Secure Airway and Ventilation FIRST

• Confirm adequate oxygenation and ventilation before any acid-base intervention because sodium bicarbonate generates CO₂ that requires respiratory clearance 2, 3
• Provide positive-pressure ventilation if needed and maintain SpO₂ >90% 3
• Effective ventilation is essential as the first maneuver in treating metabolic derangements 2

Immediate Bedside Glucose Check

• Hypoglycemia occurs in 28% of children presenting with metabolic acidosis 4
• Treat documented hypoglycemia (blood glucose <3 mmol/L) with 5 mL/kg of 10% dextrose 2
• Maintain fluids containing 5-10% glucose to prevent recurrent hypoglycemia 2

Diagnostic Algorithm

Step 1: Calculate the Anion Gap

• Anion gap = Na⁺ - (Cl⁻ + HCO₃⁻) to categorize the acidosis 5, 6
• Normal anion gap: 8-12 mEq/L 6

Step 2: Categorize by Anion Gap

High Anion Gap Metabolic Acidosis (represents unmeasured anions)

Common etiologies in ICU children:

• Lactic acidosis from hypoxia, sepsis, shock, or tissue hypoperfusion 5, 7
• Ketoacidosis from diabetes, starvation, or inborn errors of metabolism 2
• Organic acidemias (methylmalonic, propionic, isovaleric acidemia, MSUD) 2
• Toxic ingestions (ethylene glycol, methanol, salicylates) 2
• Renal failure with uremic acid accumulation 6

Normal Anion Gap (Hyperchloremic) Metabolic Acidosis

Common etiologies in ICU children:

• Iatrogenic chloride overload from 0.9% saline resuscitation—the dominant cause post-resuscitation 7
• Renal tubular acidosis (check urine pH and anion gap to distinguish proximal vs. distal) 5
• Diarrhea/gastroenteritis with bicarbonate losses 5, 4
• Excessive chloride in parenteral nutrition (especially preterm infants) 3

Step 3: Additional Diagnostic Studies

For high anion gap acidosis:

• Serum lactate (lactic acidosis from sepsis, shock, hypoxia) 7
• Blood glucose and ketones (diabetic or starvation ketoacidosis) 2
• Urine organic acids (organic acidemias, toxic ingestions) 2
• Serum osmolal gap (toxic alcohols) 6
• Blood urea nitrogen and creatinine (renal failure) 6

For normal anion gap acidosis:

• Urine pH and urine anion gap (renal tubular acidosis) 5
• Review fluid resuscitation history and calculate cumulative chloride administered 7
• Stool losses assessment (diarrhea) 4

Etiology-Specific Management

Lactic Acidosis from Shock/Sepsis

• Restore tissue perfusion with volume resuscitation: 20 mL/kg bolus of lactated Ringer's solution (preferred over normal saline) 1
• Treat underlying sepsis with broad-spectrum antibiotics (e.g., ceftriaxone 100 mg/kg/day) 2
• Metabolic acidosis resolves with correction of hypovolemia and adequate tissue perfusion—bicarbonate is NOT indicated 2, 1

Hyperchloremic Acidosis from Iatrogenic Chloride Overload

• This is the dominant cause post-resuscitation, developing by 8-12 hours after fluid administration 7
• Base excess changes by approximately -0.4 mmol/L for each mmol/kg of chloride administered 7
• Switch from chloride-containing fluids to acetate-based, chloride-free solutions 3
• Consider furosemide to enhance chloride excretion if urine output is adequate 7

Diabetic Ketoacidosis

• Focus on continuous IV insulin, fluid resuscitation, and electrolyte replacement—NOT bicarbonate 1
• Restoration of circulatory volume and tissue perfusion is the primary goal 1
• Bicarbonate has NOT been shown to improve resolution of acidosis or time to discharge 1
• Only consider bicarbonate if pH <6.9 (rare in children) 1

Organic Acidemias

• Consult specialized metabolic team immediately 2
• Provide IV glucose to prevent catabolism and metabolic decompensation 2
• Avoid prolonged fasting (e.g., before procedures) as this precipitates metabolic crisis 2
• Consider liver transplantation for frequent decompensation episodes unresponsive to medical management 2

Renal Tubular Acidosis

• Normalize serum bicarbonate with oral sodium bicarbonate (2-4 g/day or 25-50 mEq/day) 1
• Normalization is critical for normal growth parameters in children 1

Bicarbonate Therapy: When and How

Indications (ALL criteria must be met)

• pH <7.2 AND base deficit >10 mmol/L AND serum bicarbonate <12 mmol/L 3
• Only AFTER adequate ventilation is confirmed 2, 3
• Only AFTER addressing the underlying cause 1

Dosing

• 1-2 mEq/kg IV/IO given slowly 2, 1
• Use only 0.5 mEq/mL concentration for neonates 2
• Flush cannula with normal saline before subsequent infusions 2

Critical Caveats

• Bicarbonate generates CO₂, worsening intracellular acidosis if ventilation is inadequate 3
• May reduce ionized calcium, produce hyperosmolality, and worsen intracellular acidosis 1
• Do NOT mix with vasoactive amines or calcium 2
• Routine use in cardiac arrest is NOT recommended 2

Electrolyte Monitoring and Correction

Hyperkalemia (common with acidosis)

• Acidosis causes transcellular potassium shift, leading to hyperkalemia 2, 1
• Treat hyperkalemia per Advanced Paediatric Life Support guidelines if K⁺ elevated 1
• Monitor potassium closely as acidosis correction may unmask hypokalemia 2

Other Electrolyte Abnormalities

• Check and correct: potassium (<3.5 mmol/L), total calcium (<2 mmol/L), magnesium (<0.75 mmol/L), phosphate (<0.7 mmol/L) 2
• Perform arterial blood gas and electrolyte panels every 2-4 hours during active treatment 3

Common Pitfalls to Avoid

• Do NOT give bicarbonate before confirming adequate ventilation 2, 3
• Do NOT use bicarbonate routinely—it does not improve mortality in most acute organic acidoses 1
• Do NOT overlook iatrogenic hyperchloremic acidosis from normal saline resuscitation 7
• Do NOT use normal saline for volume boluses—use lactated Ringer's instead 1
• Do NOT forget to check glucose immediately—hypoglycemia is present in 28% of cases 4
• Do NOT delay treatment of underlying shock/sepsis while focusing on pH correction 2, 1

Disposition and Monitoring

• ICU-level care with continuous cardiorespiratory monitoring 1
• Arterial blood gas every 2-4 hours during active treatment 3
• Serum electrolytes (Na⁺, K⁺, ionized Ca²⁺, Mg²⁺, PO₄³⁻) every 2-4 hours 3
• Consider nephrology consultation if severe acidosis with acute kidney injury (pH <7.20) for urgent dialysis 1
• Metabolic team consultation if organic acidemia suspected 2