From the Guidelines
The interpretation of Arterial Blood Gas (ABG) results should prioritize identifying respiratory acidosis, hypercapnia, or metabolic acidosis, and guiding oxygen therapy to maintain target oxygen saturation ranges, as outlined in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1.
Key Considerations
- The BTS guideline recommends checking blood gases in critically ill patients, those with unexpected or inappropriate falls in SpO2, deteriorating oxygen saturation, or increasing breathlessness 2.
- Patients at risk of hypercapnic respiratory failure, such as those with severe or moderate COPD, should have target saturation ranges of 88-92% or levels on alert cards whilst awaiting blood gas results 1.
- For patients not at risk of hypercapnic respiratory failure, the aim is for SpO2 94-98% 1.
ABG Interpretation
- A pH < 7.35 and PCO2 > 6.0 kPa indicates respiratory acidosis and hypercapnia, requiring immediate senior review and consideration of non-invasive ventilation (NIV) or invasive ventilation 1.
- If the patient has a low pH and low bicarbonate, calculate the anion gap to determine if it is an anion gap metabolic acidosis or non-anion gap acidosis.
- Treatment should address the underlying cause of the acid-base disorder, and additional laboratory values, such as electrolytes, lactate, and kidney function tests, should be obtained to guide management.
Oxygen Therapy
- Oxygen therapy should be titrated to maintain target oxygen saturation ranges, and repeat blood gases should be checked at 30-60 minutes to assess the response to oxygen therapy 1.
- If the target saturation is not achieved, senior review and urgent treatment should be sought.
- The BTS guideline provides a framework for oxygen prescription, including the use of reservoir masks, bag-valve masks, and nasal oxygen, to achieve target oxygen saturation ranges 1.
From the Research
Interpretation of Arterial Blood Gas (ABG) Results
The interpretation of ABG results is a crucial skill in healthcare practice, particularly when caring for acutely unwell or deteriorating patients 3, 4, 5, 6. ABG analysis assesses the adequacy of ventilation, oxygenation, and the acid-base status of the body by measuring the levels of pH, oxygen, carbon dioxide, and bicarbonate in arterial blood 4, 6.
Key Components of ABG Results
The key components of ABG results include:
- pH: measures the acid-base balance of the blood 3, 4, 5, 6
- PaCO2: measures the partial pressure of carbon dioxide in the blood, indicating ventilation status 3, 4, 5, 6
- PaO2: measures the partial pressure of oxygen in the blood, indicating oxygenation status 3, 4, 5, 6
- HCO3: measures the bicarbonate level in the blood, indicating metabolic status 3, 4, 5, 6
- SaO2: measures the oxygen saturation of hemoglobin in the blood 5
Analyzing ABG Results
ABG results can be analyzed using various techniques, including the RoMe technique, which uses the three main values of pH, PaCO2, and HCO3 to determine acid-base imbalances 3. The results can also be interpreted by assessing the patient's oxygenation status, compensation levels, and determining if there is an acid-base disturbance and if that disturbance is respiratory or metabolic 5.
Clinical Applications of ABG Analysis
ABG analysis has various clinical applications, including:
- Assessing patients' acid-base balance and gas exchange 3, 4, 5, 6
- Informing appropriate care and management of patients with pulmonary and other critical conditions 4, 6
- Diagnosing and treating patients with acid-base diseases, such as severe sepsis, septic shock, and diabetic ketoacidosis 6
- Evaluating the effectiveness of ventilatory support and oxygen therapy 7, 6