Acid-Base Disorders Lecture Notes

Introduction

• Lecture on acid-base disorders as part of clinical medicine.
• Four primary disorders:
  • Metabolic acidosis
  • Metabolic alkalosis
  • Respiratory acidosis
  • Respiratory alkalosis

Metabolic Acidosis

Anion Gap Metabolic Acidosis (AGMA)

• Anion Gap Calculation: Sodium - (Chloride + Bicarb)
• High Anion Gap (>12): Indicates excess organic acids.
• Causes:
  • Diabetic Ketoacidosis (DKA): High glucose and ketone bodies.
  • Uremic Acidosis: Kidney failure related.
  • Lactic Acidosis: Poor perfusion or impaired oxidative phosphorylation.
  • Toxic Ingestions: Methanol, ethylene glycol.
• Complications:
  • Hyperkalemia leading to arrhythmias.
  • Respiratory compensation: Hyperventilation.
  • Myocardial contractility inhibition in severe acidosis.

Non-Anion Gap Metabolic Acidosis (NAGMA)

• Anion Gap <=12
• Causes:
  • Renal losses: CKD, various RTAs.
  • GI losses: Diarrhea, pancreatic fistulas.
• Diagnostic:
  • Urine anion gap helps differentiate renal from GI causes.

Metabolic Alkalosis

• Causes:
  • Renal loss of protons.
  • GI loss (vomiting, NG suction).
• Complications:
  • Hypokalemia leading to arrhythmias.
  • Possible hypoventilation.
  • Tetany due to hypocalcemia.

Respiratory Acidosis

• Causes:
  • Hypoventilation due to respiratory center depression, neuromuscular disease, or airway obstruction.
• Complications:
  • Increased intracranial pressure leading to altered mental status.
  • Renal compensation by increasing bicarbonate reabsorption.

Respiratory Alkalosis

• Causes:
  • Hyperventilation due to anxiety, pain, hypoxemia.
• Complications:
  • Cerebral vasoconstriction, potential syncope.
  • Renal compensation through increased bicarbonate excretion.

Diagnostics

• Arterial Blood Gas (ABG):
  • pH < 7.35: Acidosis
  • pH > 7.45: Alkalosis
• Anion Gap Calculation for metabolic acidosis.
• Delta-delta ratio for mixed acid-base disorders.

Treatment

Metabolic Acidosis

• DKA: Insulin administration.
• Lactic Acidosis: Treat underlying shock or remove offending drugs.
• Uremic Acidosis: Sodium bicarbonate or dialysis.
• Toxic Ingestions: Fomepizole and potential use of dialysis.

Metabolic Alkalosis

• Hypovolemic: Normal saline for volume and chloride replacement.
• Hypervolemic: Acetazolamide in CHF, potassium chloride supplementation.

Respiratory Disorders

• Acidosis:
  • Treat drug overdoses with antidotes.
  • COPD/asthma: Bronchodilators, steroids, BiPAP.
• Alkalosis:
  • Pain/anxiety: Analgesia or anxiolytics.
  • Hypoxemia: Oxygen therapy.