Interpretation of Arterial Blood Gas (ABG) Analysis

Understanding Normal ABG Values and Their Clinical Significance

Arterial Blood Gas (ABG) analysis is a vital diagnostic tool used to assess a patient's respiratory and metabolic status by measuring key parameters such as pH, partial pressures of oxygen and carbon dioxide (PaO2, PaCO2), bicarbonate (HCO3-), and oxygen saturation.

Normal ABG Values

• pH: 7.35 - 7.45
• PaCO2: 35 - 45 mmHg
• HCO3-: 22 - 26 mEq/L
• PaO2: 80 - 100 mmHg
• O2 Saturation: 95 - 100%

Clinical Interpretation

Acidosis vs. Alkalosis

Acidosis occurs when blood pH is below 7.35, whereas alkalosis occurs when blood pH is above 7.45. These conditions can be respiratory or metabolic in nature:

• Respiratory Acidosis: Increased PaCO2, decreased pH (e.g., COPD, hypoventilation)
• Respiratory Alkalosis: Decreased PaCO2, increased pH (e.g., hyperventilation, anxiety)
• Metabolic Acidosis: Decreased HCO3-, decreased pH (e.g., diabetic ketoacidosis, renal failure)
• Metabolic Alkalosis: Increased HCO3-, increased pH (e.g., vomiting, excessive bicarbonate intake)

Compensatory Mechanisms

The body attempts to normalize pH through compensatory mechanisms:

• Respiratory Compensation: Lungs regulate PaCO2 through changes in ventilation.
• Renal Compensation: Kidneys adjust HCO3- levels to stabilize pH.

Conclusion

ABG analysis is crucial in evaluating a patient’s acid-base status, guiding clinical decisions, and monitoring treatment effectiveness. Understanding its interpretation ensures prompt diagnosis and intervention in critical conditions.