Acid Base Balance NUR 612 Pathophysiology

Acid-Base Balance Overview

• Acid-base balance is crucial for understanding physiological processes in patient care.

• While primary care may not often involve acutely ill patients, knowledge of acid-base balance is foundational for future care.

Definitions of Acids and Bases

• Acid: A substance that donates a hydrogen ion (H+).

• Base: A substance that receives a hydrogen ion.

• Physiological pH: Normal range is 7.35 to 7.45, with an ideal pH of 7.4.

Role of Carbon Dioxide

• Carbon Dioxide (CO2): A byproduct of cellular metabolism that primarily combines with water to form carbonic acid (H2CO3), a weak acid.

• CO2 is expelled by the lungs, while kidneys manage bicarbonate (HCO3-) and hydrogen ions (H+).

The Carbonic Acid-Bicarbonate Buffer System

• The ratio of carbonic acid to bicarbonate is typically maintained at 20:1. Imbalances lead to clinical issues.

• Buffer System: Circulating bicarbonate buffers excess acids by binding to hydrogen ions.

Transcellular Shifting of Ions

• During acidemia, hydrogen ions move into cells, displacing potassium (K+) into the serum, leading to hyperkalemia.

• Conversely, alkalemia causes potassium to enter cells, leading to hypokalemia.

Compensatory Mechanisms

• Respiratory Compensation: Alters CO2 levels via breathing rate. Quick fix but less effective than renal compensation.

• Renal Compensation: Takes longer but effectively regulates bicarbonate and hydrogen ion levels.

Types of Acid-Base Imbalances

• Respiratory Acidemia/Alkalemia: Issues originate in the lungs.

  • High CO2 indicates respiratory acidemia.

  • Low CO2 indicates respiratory alkalemia.

• Metabolic Acidosis/Alkalemia: Issues originate from metabolic processes.

  • Loss of bicarbonate or gain of acids indicates metabolic acidosis.

  • Gain of bicarbonate or loss of acids indicates metabolic alkalemia.

Anion Gap

• Anion Gap Calculation: Sodium - (Bicarbonate + Chloride). Normal range is 10-12.

• A high anion gap indicates acidosis and potential additional acids in the system.

Key Disturbances and Their Causes

• High Anion Gap Acidosis Causes: Measured by the acronym MUDPILES (Methanol, Uremia, DKA, Paraldehyde, Infection, Lactic Acidosis, Salicylate).

• Metabolic Acidosis: Can arise from diarrhea (loss of base) or acid gain (e.g., DKA).

• Metabolic Alkalosis: Caused by vomiting or excessive bicarbonate intake.

Clinical Assessment Steps

1. Calculate the anion gap to determine if there is acidosis.

2. Analyze pH: low indicates acidemia; high indicates alkalemia.

3. Evaluate CO2: Determines respiratory vs. metabolic origin (ROME: Respiratory opposite, Metabolic equal).

4. Use clinical context and patient history for accurate diagnosis and treatment.