Metabolic Acidosis: A Comprehensive Guide for OPRA Exam Preparation

What is Metabolic Acidosis?

Metabolic acidosis is a condition characterized by a decrease in blood pH (< 7.35) due to an increase in acid levels or a loss of bicarbonate. This topic is highly relevant for pharmacists preparing for the OPRA exam, as it involves critical aspects of diagnosis and management of acid-base disorders.

Pathophysiology

• Increased Acid Production: Common in conditions like lactic acidosis or diabetic ketoacidosis (DKA).
• Loss of Bicarbonate: Often caused by severe diarrhea or renal tubular acidosis.
• Decreased Renal Acid Excretion: Frequently observed in chronic kidney disease (CKD).

Clinical Features of Metabolic acidosis

• Respiratory Compensation: Deep, rapid breathing (Kussmaul respiration).
• Neurological Symptoms: Fatigue, confusion, or in severe cases, coma.
• Cardiac Impact: Arrhythmias due to associated hyperkalemia.

Diagnosis

Accurate diagnosis is essential for managing metabolic acidosis. Key steps include:

1. Arterial Blood Gas (ABG): Reveals low pH and low bicarbonate (HCO₃⁻).
2. Anion Gap Calculation:

   Formula: Anion Gap = Na⁺ - (Cl⁻ + HCO₃⁻)

   • Normal AG: Seen in diarrhea or renal tubular acidosis.
   • Elevated AG: Indicates conditions like lactic acidosis, DKA, or toxic ingestions (e.g., methanol, salicylates).

Management

Effective management focuses on treating the underlying cause and correcting the acid-base imbalance:

• Address the Cause:
  • DKA: Administer insulin and fluids.
  • Lactic Acidosis: Restore tissue perfusion.
• Bicarbonate Therapy: Considered in severe cases (pH < 7.1).
• Electrolyte Monitoring: Correct hyperkalemia to prevent complications.

OPRA Exam Tips

For the OPRA exam, focus on:

• Understanding the difference between normal and elevated anion gap metabolic acidosis.
• ABG interpretation and clinical scenario-based questions.
• Recognizing and managing common causes like DKA and lactic acidosis.