Arterial Blood Gas Interpretation Guidelines
Standard Reference Ranges
- Normal arterial blood gas values on room air are: PO2 >90 mmHg, PCO2 <40 mmHg, and pH 7.40 1, 2, 3, 4
- The normal range for PO2 is >90 mmHg, for PCO2 is <40 mmHg, and for pH is 7.40 1, 2, 3, 4
- Normal mixed venous blood values differ significantly: PO2 of 40 mmHg, PCO2 of 50 mmHg, and pH of 7.35 1, 2, 3, 4
Clinical Context for Interpretation
- For most patients without risk of hypercapnic respiratory failure, target SpO2 should be 94-98% 5
- Patients at risk for hypercapnic respiratory failure should target SpO2 of 88-92% 5
- A PO2 >90 mmHg typically corresponds to oxygen saturation >94% 5
- A PO2 below 60 mmHg represents life-threatening hypoxemia requiring immediate intervention 5
- Hypoxemia with PO2 <60 mmHg demands urgent oxygen supplementation regardless of PCO2 status 5
Important Clinical Caveats
- ABG measurement is crucial in critically ill patients because pulse oximetry alone cannot assess ventilation status or acid-base balance 5
- ABG provides critical information about PaCO2 and pH that pulse oximetry cannot detect 5
- After initiating or changing oxygen therapy, repeat ABG within 30-60 minutes to confirm adequate response without precipitating respiratory acidosis 5
- Respiratory acidosis is defined as pH <7.35 with PCO2 >6.0 kPa (45 mmHg), indicating inadequate ventilation 5
Respiratory Alkalosis with Severe Hypoxemia Requiring Immediate Oxygen Therapy
Oxygen Therapy Guidelines
- The American Thoracic Society recommends administering supplemental oxygen to achieve a PO2 of at least 60 mmHg (or ideally >90 mmHg) to prevent tissue hypoxia, with repeat ABG within 30-60 minutes to ensure adequate response without worsening alkalosis 6
- For controlled oxygen delivery, use Venturi masks starting at 28% FiO2 or nasal cannulae at 2 L/min if there is any concern for underlying COPD, and increase inspired oxygen concentration incrementally until PO2 exceeds 60 mmHg (ideally >90 mmHg) 6