From the Guidelines
This ABG result indicates respiratory alkalosis with no significant metabolic compensation, and the patient is not at risk of hypercapnic respiratory failure, thus aiming for an SpO2 of 94-98% is appropriate. The key findings are:
- Elevated pH (7.45) - alkalosis
- Low pCO2 (22 mmHg) - respiratory component
- High pO2 (129 mmHg) - adequate oxygenation The patient is hyperventilating, causing excessive CO2 elimination and a rise in blood pH. To address this:
- Identify and treat the underlying cause of hyperventilation (e.g., anxiety, pain, sepsis, pulmonary embolism) 1
- Monitor electrolytes, especially potassium, as alkalosis can cause hypokalemia
- Reassess ABGs after treating the underlying cause to ensure normalization
- According to the BTS guideline for oxygen use in adults in healthcare and emergency settings, for patients who are not at risk of hypercapnic respiratory failure, the target oxygen saturation should be 94-98% 1 Some important considerations include:
- Carefully measuring respiratory rate and heart rate because tachypnoea and tachycardia are more common than a physical finding of cyanosis in hypoxaemic patients 1
- Appropriate changes should be made to any ‘track and trigger’ system used to allow for a lower target range in patients at risk of hypercapnic respiratory failure, although this is not applicable in this case 1
- The 2017 BTS guideline recommends aiming for an SpO2 of 94-98% for patients who are not at risk of hypercapnic respiratory failure, which is consistent with the patient's current condition 1
From the Research
Interpretation of Arterial Blood Gas (ABG) Results
The given ABG result shows a pH of 7.45, pCO2 of 22 mmHg, and pO2 of 129 mmHg. To interpret this result, we need to consider the acid-base balance and the respiratory and metabolic components.
Acid-Base Balance
- The pH of 7.45 is higher than the normal range of 7.35-7.45, indicating alkalosis 2, 3.
- The pCO2 of 22 mmHg is lower than the normal range of 35-45 mmHg, indicating a respiratory alkalosis 4, 3.
- The pO2 of 129 mmHg is higher than the normal range of 75-100 mmHg, indicating adequate oxygenation.
Respiratory Component
- The low pCO2 level suggests hyperventilation, which can lead to respiratory alkalosis 4, 3.
- The high pO2 level suggests adequate oxygenation, which can rule out hypoxemic respiratory failure 3.
Metabolic Component
- The pH and pCO2 levels suggest a primary respiratory alkalosis, but the metabolic component needs to be evaluated to rule out any mixed disorders 5, 6.
- The absence of electrolyte and oxygen saturation results makes it difficult to fully assess the metabolic component, but the presence of alkalosis suggests that metabolic alkalosis may be present 2.
Possible Diagnosis
- Primary respiratory alkalosis with possible secondary metabolic alkalosis 3.
- Mixed respiratory and metabolic alkalosis 6, 2.
Clinical Correlation
- The interpretation of the ABG result should be correlated with the patient's clinical condition, including any symptoms, physical examination findings, and laboratory results 6, 3.
- The presence of alkalosis may indicate hyperventilation, which can be caused by various factors, including anxiety, pain, or respiratory disease 4, 3.