Metabolic Acidosis

Metabolic Acidosis: Excerpt from In A Page: Pediatric Signs and Symptoms

Metabolic acidosis (defined as a serum bicarbonate <20 mEq/L) can be due to a primary metabolic cause, or it can represent a secondary metabolic compensation for a primary respiratory process. These processes can be distinguished by evaluation of a venous (or arterial) blood gas. An acidotic pH suggests a primary metabolic acidosis; alkalotic pH suggests secondary (since the body cannot completely compensate to a normal value).

Differential Diagnosis

• Increased anion gap (AG) metabolic acidosis, due to production of exogenous acid “MUDPILES”

• Methanol
• Uremia
• DKA
• Paraldehyde
• Ingestions/inborn errors of metabolism
• Lactic acidosis
• Ethylene glycol
• Salicylates

• Normal anion gap metabolic acidosis, due to bicarbonate loss in the GI tract or kidneys or impaired acid secretion by the kidney
  –Diarrhea, other GI losses (very common)
  –Type I (distal) renal tubular acidosis (RTA): Inability to excrete hydrogen ion, urine pH always high (>6.5), caused by a variety of medications, inherited forms, or renal insufficiency; often associated with low potassium and hypercalciuria
  –Type II (proximal) RTA: Impaired reabsorption of bicarbonate from the proximal tubule, usually associated with other evidence of proximal tubule dysfunction (Fanconi syndrome), such as phosphaturia or glycosuria
  –Type IV (hyperkalemic) RTA: Inadequate aldosterone production or inability to respond appropriately to aldosterone; commonly seen in patients with a history of obstructive uropathy or as a transient occurrence in patients with acute pyelonephritis

Workup and Diagnosis

• History
  –Symptoms of fever, flank pain and vomiting (pyelonephritis), lethargy/altered mental status (intoxication or metabolic disease)
  – GI losses (diarrhea), ingestions, poor growth, increased or decreased urine output, history of urinary tract abnormalities (e.g., congenital obstructive uropathy)
  –Family history of kidney disease, kidney stones, metabolic disease, early infant deaths

• Physical exam: Assessment of hydration status (heart rate, blood pressure, mucous membranes, skin perfusion), growth parameters, respiratory status (tachypnea suggests either primary respiratory process or respiratory compensation for severe metabolic acidosis) abdominal exam, complete neurologic exam
• Labs
  –Chemistry panel
  –Calculation of AG =[Na⁺] – [HCO_3- +Cl^–]; normal =10–12; when increased anion gap is due to exogenous acid, AG is often ≥20
  –Venous blood gas, if the etiology of the acidosis is unclear (i.e., primary vs secondary); urinalysis (to help distinguish proximal vs distal RTA)
  • Additional evaluation based on the clinical situation, e.g., toxicology, metabolic screens (increased AG acidosis), renal ultrasound (nephrocalcinosis with type I RTA)

  Treatment

  • If primary respiratory process identified, then treat the cause and the acidosis will resolve over time
  • Dehydration: Oral or IV fluid replacement; even with normalization of fluid status, improvement in serum bicarbonate may not occur for 2–3 days
  • For primary metabolic process
    –Estimate deficit =20 – [HCO₃] ×Weight (kg) ×0.5
    –Replace over 24–48 hours with oral bicarbonate (e.g. bicitra solution 1 cc =1 meq) or IV bicarbonate added to IV fluids; IV sodium bicarbonate “boluses” should be avoided unless acidosis is severe or symptomatic
  • Increased AG acidosis: Identify and treat cause
  • Distal or proximal RTA: Usually requires bicarbonate supplementation
  • Hyperkalemic RTA: Correct serum bicarbonate, increase fluids to improve sodium delivery to distal tubule to enhance potassium secretion
  >

Book Source Details

• Book Title: In A Page: Pediatric Signs and Symptoms
• Author(s): Jonathan E. Teitelbaum, Kathleen O. Deantonis, Scott Kahan
• Year of Publication: 2007
• Copyright Details: In A Page: Pediatric Signs and Symptoms, Copyright © 2007 Lippincott Williams & Wilkins.

More About Metabolic disorders

• Back to disease: Metabolic disorders: Introduction
• Next Book Extract About Metabolic disorders: Bibliography: Endocrine/Metabolic System (A Pocket Manual of Differential Diagnosis)
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: In A Page: Pediatric Signs and Symptoms Authors: Jonathan E. Teitelbaum, Kathleen O. Deantonis, Scott Kahan Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 1-4051-0427-9

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• Bibliography: Endocrine/Metabolic System (A Pocket Manual of Differential Diagnosis)
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