Errors in arterial blood gas (ABG) analysis can occur during several phases of the testing process. The most frequent problems arise during the preanalytical phase, which involves sample collection and handling before analysis.
Preanalytical Errors: The Most Common Culprits
The preanalytical phase is where the majority of ABG errors originate, accounting for up to 75% of all mistakes. [¹][²][³][⁴][⁵][¹⁰] These errors are preventable and often stem from human input during sample collection and handling. [²] Common preanalytical errors include:
- Nonarterial Samples: Using a venous blood sample instead of arterial blood significantly alters the results, as venous blood has different gas partial pressures.
- Air Bubbles in the Sample: Air bubbles in the sample contaminate the specimen, leading to inaccurate readings of oxygen levels (pO2).
- Inadequate or Excessive Anticoagulant: Too little anticoagulant can lead to clotting, while too much can dilute the sample and affect the results.
- Delayed Analysis of an Un-cooled Sample: Delaying analysis, particularly without cooling, allows for changes in gas values within the sample. While results may remain reliable for up to an hour at room temperature with careful handling to minimize air, prompt analysis is ideal. [⁶]
Other Sources of Error
Beyond the preanalytical phase, errors can occur in the analytical and post-analytical stages. [⁷][⁸] While less frequent than preanalytical errors, these should also be considered:
- Analytical Errors: These involve inaccuracies in the blood gas analyzer's functioning, calibration issues, or faulty equipment.
- Post-analytical Errors: These occur after the analysis is complete, and include misreporting, misinterpretation of results, or errors in data entry. For example, failure to consider the patient's FiO2 (fraction of inspired oxygen) and barometric pressure can lead to misinterpretation of oxygenation status. [⁷]
Additional factors contributing to preanalytical errors include: inappropriate test ordering, order entry errors, patient/specimen misidentification, and sample contamination (e.g., from indwelling catheters). [⁴]
Minimizing Errors
Improving sample collection techniques is crucial to minimize preanalytical errors. [⁵] This includes proper patient identification, correct puncture site selection (radial artery preferred), and careful handling of the sample to avoid air bubbles and contamination. Timely analysis and appropriate storage (cooling if immediate analysis is not possible) also help maintain sample integrity. [⁶]
