Acid-Base Balance and ABG Interpretation

Normal Values

• pH: 7.35-7.45
• pCO2: 35-45 mmHg
• pO2: 75-100 mmHg
• HCO3-: 22-28 mmol/L
• Base Excess: -2 to +2 mmol/L

Acid-Base Disorders

• Acidosis: pH < 7.35
  • Respiratory acidosis: pCO2 > 45 mmHg
  • Metabolic acidosis: HCO3- < 22 mmol/L
• Alkalosis: pH > 7.45
  • Respiratory alkalosis: pCO2 < 35 mmHg
  • Metabolic alkalosis: HCO3- > 28 mmol/L

Steps to Interpret ABG

1. Check pH: Is the patient acidic or alkalotic?
2. Determine the primary disorder: Is it respiratory or metabolic?
3. Check for compensation: Is the body compensating for the primary disorder?
   • Respiratory compensation: pCO2 changes in response to metabolic disorder
   • Metabolic compensation: HCO3- changes in response to respiratory disorder
4. Check for mixed disorders: Is there a combination of respiratory and metabolic disorders?

Examples of ABG Interpretation

• Respiratory acidosis: pH 7.20, pCO2 60 mmHg, HCO3- 24 mmol/L
  • Primary disorder: Respiratory acidosis (high pCO2)
  • Compensation: Metabolic compensation (increased HCO3-)
• Metabolic acidosis: pH 7.25, pCO2 30 mmHg, HCO3- 18 mmol/L
  • Primary disorder: Metabolic acidosis (low HCO3-)
  • Compensation: Respiratory compensation (low pCO2)

Common Causes of Acid-Base Disorders

• Respiratory acidosis: COPD, pneumonia, respiratory failure
• Metabolic acidosis: diabetic ketoacidosis, lactic acidosis, renal failure
• Respiratory alkalosis: hyperventilation, anxiety, pneumonia
• Metabolic alkalosis: vomiting, diuretic use, excessive bicarbonate intake

Normal Values

• pH ranges from 7.35 to 7.45
• pCO2 ranges from 35 to 45 mmHg
• pO2 ranges from 75 to 100 mmHg
• HCO3- ranges from 22 to 28 mmol/L
• Base Excess ranges from -2 to +2 mmol/L

Acid-Base Disorders

Acidosis

• pH is less than 7.35
• Respiratory acidosis: pCO2 is greater than 45 mmHg
• Metabolic acidosis: HCO3- is less than 22 mmol/L

Alkalosis

• pH is greater than 7.45
• Respiratory alkalosis: pCO2 is less than 35 mmHg
• Metabolic alkalosis: HCO3- is greater than 28 mmol/L

Steps to Interpret ABG

• Check pH to determine if the patient is acidic or alkalotic
• Determine the primary disorder: respiratory or metabolic
• Check for compensation: respiratory or metabolic
• Check for mixed disorders: combination of respiratory and metabolic disorders

ABG Interpretation Examples

Respiratory Acidosis

• pH is 7.20
• pCO2 is 60 mmHg
• HCO3- is 24 mmol/L
• Primary disorder: respiratory acidosis
• Compensation: metabolic compensation

Metabolic Acidosis

• pH is 7.25
• pCO2 is 30 mmHg
• HCO3- is 18 mmol/L
• Primary disorder: metabolic acidosis
• Compensation: respiratory compensation

Common Causes of Acid-Base Disorders

• Respiratory acidosis: COPD, pneumonia, respiratory failure
• Metabolic acidosis: diabetic ketoacidosis, lactic acidosis, renal failure
• Respiratory alkalosis: hyperventilation, anxiety, pneumonia
• Metabolic alkalosis: vomiting, diuretic use, excessive bicarbonate intake