Acid-Base Disorders Lecture Notes

Introduction

• Overview of acid-base disorders as part of clinical medicine.
• Importance of premium resources for study aids.

Types of Acid-Base Disorders

1. Metabolic Acidosis

   • Subtypes: Anion Gap Metabolic Acidosis (AGMA) and Non-Anion Gap Metabolic Acidosis (NAGMA).
   • Pathophysiology includes cations and anions in extracellular fluid.
   • Anion Gap Calculation: Na - (Cl + HCO3)
   • Elevation: AG > 12 indicates presence of excess organic acids.
   • Organic acids release protons, depleting bicarbonate (HCO3), lowering pH.

2. Metabolic Alkalosis

   • Related to renal loss of protons or gastrointestinal loss (vomiting, suctioning).
   • High bicarbonate levels lead to increased pH.

3. Respiratory Acidosis

   • Caused by hypoventilation, leading to CO2 retention.
   • Increased CO2 leads to decreased pH.
   • Causes: Respiratory center dysfunction, neuromuscular diseases, airway obstruction.

4. Respiratory Alkalosis

   • Result of hyperventilation, leading to decreased CO2 and increased pH.
   • Causes: Anxiety, pain, hypoxemia.

Metabolic Acidosis

Anion Gap Metabolic Acidosis (AGMA)

• AG > 12 indicates increased organic acids (e.g., diabetic ketoacidosis, lactic acidosis).
• Common causes include:
  • Diabetic Ketoacidosis: High glucose and ketone bodies due to insufficient insulin.
  • Uremic Acidosis: Poor kidney function leads to acid retention.
  • Lactic Acidosis: Poor perfusion or interference with oxidative phosphorylation.
  • Toxic Ingestion: Methanol and ethylene glycol, causing acid buildup.

Non-Anion Gap Metabolic Acidosis (NAGMA)

• AG ≤ 12 indicates loss of bicarbonate, often from renal or GI losses.
• Renal Losses: Chronic kidney disease (CKD), renal tubular acidosis (RTA).
• GI Losses: Diarrhea, pancreatic fistulas.

Complications of Metabolic Acidosis

• Electrolyte disturbances: Hyperkalemia due to proton shift into cells.
• Respiratory compensation: Increased ventilation to blow off CO2.
• Cardiac effects: Myocardial contractility inhibited at very low pH (pH < 7.15).

Metabolic Alkalosis

• Caused by loss of protons through GI (vomiting, NG suction) or renal losses.
• Increased bicarbonate leads to increased pH.
• Complications: Hypokalemia, potential for arrhythmias, and muscle twitching due to low calcium.

Respiratory Acidosis

• Caused by hypoventilation leading to CO2 retention.
• Complications: Increased intracranial pressure, lethargy, confusion.
• Causes: Obstruction (COPD, asthma), neurological issues, drug overdoses.

Respiratory Alkalosis

• Caused by hyperventilation, leading to decreased CO2 and increased pH.
• Causes: Anxiety, pain, hypoxia.
• Complications: Dizziness, syncope due to reduced cerebral blood flow.

Diagnostic Approach

• Arterial Blood Gas (ABG): Key to diagnosing acid-base disorders.
• Identify if acidosis (<7.35) or alkalosis (>7.45), then determine if metabolic or respiratory.
• For metabolic acidosis, calculate anion gap and urine anion gap.
• For metabolic alkalosis, assess volume status (hypovolemic vs. hypervolemic).

Treatment Overview

• Metabolic Acidosis: Treat underlying cause, e.g., insulin for DKA, fluids for lactic acidosis.
• Metabolic Alkalosis: Correct hypovolemia with fluids or address hyperaldosteronism.
• Respiratory Acidosis: Address hypoventilation, potential use of BiPAP in COPD.
• Respiratory Alkalosis: Treat underlying cause (pain, hypoxia).

Conclusion

• Summary of key points on acid-base balance in clinical settings.
• Importance of understanding pathophysiology for effective treatment.