Acid- Base Balance

Acid-Base Balance Overview

• Normal pH range for extracellular fluid: 7.35 to 7.45

• Mechanisms of pH balance:

  • Generate, buffer, and eliminate acids and bases.

Definitions

Acid

• Definition: Molecule that releases hydrogen (H+).

• Example: Hydrochloric acid (HCl) dissociates in water to form H+ and Cl-.

Base

• Definition: Ion or molecule that accepts or combines with hydrogen.

• Example: Bicarbonate (HCO3-) combines with H+ to form carbonic acid (H2CO3), a weak acid.

pH Regulation Mechanisms

1. Chemical Buffer System

   • Combines with excessive acids or bases to prevent large changes in pH.

2. Lungs

   • Control elimination of CO2.

3. Kidneys

   • Eliminate H+ (acidic) and reabsorb/generate new HCO3- (bicarbonate).

Mnemonics for pH Variations

• ROAM:

  • Respiratory: Opposite

  • Metabolic: Equal

• pH Standards:

  • Acidosis: pH < 7.35

  • Alkalosis: pH > 7.45

Details on Respiratory and Metabolic Functions

Respiratory System

• Opposite Relation: High pH → Low CO2 (Alkalosis)

• Indicators of Acidosis: Low pH → High CO2 (Hypoventilation)

• Normal Respiratory Rate: 12 to 20 breaths per minute.

Metabolic System

• Equal Relation:

  • High pH → High HCO3- (Alkalosis)

  • Low pH → Low HCO3- (Acidosis)

• Bicarbonate Normal Range: 22 to 26 mEq/L

Arterial Blood Gases (ABG) Collection

• Collected from radial artery using a needle at a 90-degree angle.

• Differentiation: Arterial blood is bright red; venous blood is dark/purple.

Acid-Base Disorders

Respiratory Acidosis

• Causes: Drug overdose, lung diseases, impaired ventilation.

• Presentation:

  • Low pH, high CO2, normal HCO3- (uncompensated) or high HCO3- (compensated).

  • Symptoms: Headaches, confusion, drowsiness.

Respiratory Alkalosis

• Causes: Panic attacks, hypoxia, drug reactions.

• Presentation:

  • High pH, low CO2, normal HCO3-.

  • Symptoms: Dizziness, lightheadedness, seizures.

Metabolic Acidosis

• Causes: Excessive production of lactic acid, renal failure, diabetic ketoacidosis.

• Presentation:

  • Low pH, low HCO3-, normal/high CO2.

  • Symptoms: Nausea, confusion, lethargy.

Metabolic Alkalosis

• Causes: Ingestion of antacids, GI loss of acid (vomiting), diuretics.

• Presentation:

  • High pH, high HCO3-, normal CO2.

  • Symptoms: Confusion, hypokalemia, seizures.

Compensation Mechanisms

• Respiratory System: Rapid response (within 30 minutes) for pH adjustment; effective but only 50-75% as a buffer.

• Kidneys: Slower response (5-10 minutes to begin; 3-5 days to complete).

• Compensation Levels:

  • Uncompensated: One parameter normal, one abnormal.

  • Partially Compensated: Both parameters abnormal, pH still abnormal.

  • Fully Compensated: Normal pH, both parameters abnormal.

  • Determining Compensation:

    • pH normal = fully compensated.

    • pH abnormal = partially compensated.

    • One normal parameter indicates uncompensated.

Key Values to Remember

• Normal CO2: 35 to 45 mmHg

• Normal HCO3-: 22 to 26 mEq/L

Summary

• Strong emphasis on memorizing the acid-base ranges, mnemonics, and clinical presentations associated with different disorders.

• Students encouraged to practice identifying and interpreting ABG values and understanding the primary disorder and compensation status.

• Importance of understanding these concepts for nursing practice and exam preparation.