ABG Interpretation

ABG Interpretation

Normal Values

• pH: 7.35-7.45
• pCO2: 35-45 mmHg
• HCO3-: 22-29 mEq/L
• O2 saturation: 95-100%

Steps of ABG Interpretation

1. Determine the primary disorder:
   • Respiratory acid-base disturbance: pCO2 abnormal, pH normal or opposite direction
   • Metabolic acid-base disturbance: HCO3- abnormal, pH normal or opposite direction
2. Determine the compensatory response:
   • Respiratory response to metabolic acid-base disturbance: pCO2 changes in same direction as HCO3-
   • Metabolic response to respiratory acid-base disturbance: HCO3- changes in same direction as pCO2
3. Evaluate the effectiveness of compensation:
   • If pH is normal, compensation is effective
   • If pH is abnormal, compensation is incomplete or absent
4. Determine if a mixed disorder is present:
   • Check for inconsistencies between pCO2, HCO3-, and pH

Acid-Base Disorders

Respiratory Acidosis

• pH < 7.35
• pCO2 > 45 mmHg
• Caused by: respiratory failure, COPD, pneumonia, etc.

Respiratory Alkalosis

• pH > 7.45
• pCO2 < 35 mmHg
• Caused by: hyperventilation, anxiety, pneumonia, etc.

Metabolic Acidosis

• pH < 7.35
• HCO3- < 22 mEq/L
• Caused by: diabetic ketoacidosis, lactic acidosis, renal failure, etc.

Metabolic Alkalosis

• pH > 7.45
• HCO3- > 29 mEq/L
• Caused by: vomiting, diuretic use, hypokalemia, etc.

Other Considerations

• Anion gap: calculate to identify unmeasured anions (e.g., lactate, ketones) in metabolic acidosis
• Base excess: calculate to evaluate the severity of acid-base disorders

ABG Interpretation

Normal Values

• pH ranges from 7.35 to 7.45
• pCO2 ranges from 35 to 45 mmHg
• HCO3- ranges from 22 to 29 mEq/L
• O2 saturation ranges from 95 to 100%

Steps of ABG Interpretation

• Determine the primary disorder by checking if pCO2 is abnormal for respiratory issues or HCO3- is abnormal for metabolic issues
• Determine the compensatory response by checking if pCO2 changes in the same direction as HCO3- for metabolic acid-base disturbances, or if HCO3- changes in the same direction as pCO2 for respiratory acid-base disturbances
• Evaluate the effectiveness of compensation by checking if pH is normal or abnormal
• Determine if a mixed disorder is present by checking for inconsistencies between pCO2, HCO3-, and pH

Acid-Base Disorders

Respiratory Acidosis

• Characterized by pH < 7.35 and pCO2 > 45 mmHg
• Caused by respiratory failure, COPD, pneumonia, etc.

Respiratory Alkalosis

• Characterized by pH > 7.45 and pCO2 < 35 mmHg
• Caused by hyperventilation, anxiety, pneumonia, etc.

Metabolic Acidosis

• Characterized by pH < 7.35 and HCO3- < 22 mEq/L
• Caused by diabetic ketoacidosis, lactic acidosis, renal failure, etc.

Metabolic Alkalosis

• Characterized by pH > 7.45 and HCO3- > 29 mEq/L
• Caused by vomiting, diuretic use, hypokalemia, etc.

Other Considerations

• Anion gap calculation helps identify unmeasured anions (e.g., lactate, ketones) in metabolic acidosis
• Base excess calculation evaluates the severity of acid-base disorders

Learn how to interpret arterial blood gas (ABG) values, including normal ranges and steps to determine primary disorders and compensatory responses.