Validating Arterial Blood Gas Results
To validate the results of an Arterial Blood Gas (ABG) test, arterial or venous whole blood sampling should be used instead of finger-stick capillary blood glucose testing for patients in shock, on vasopressor therapy, or with severe peripheral edema, and for any patient on a prolonged insulin infusion. 1
Key Validation Methods for ABG Results
1. Sample Collection Validation
- Proper arterial sampling: Arterial samples are preferred over capillary samples for accuracy 2
- Allen's test: Perform before radial artery sampling to ensure dual blood supply to the hand 2
- Proper labeling: Include unique patient identifiers, date, time, and collector's identification 2
- Use of local anesthesia: Should be used for all ABG specimens except in emergencies 2
2. Pre-analytical Error Prevention
- Temperature control: If immediate analysis is not possible, store samples at room temperature for up to 60 minutes 3
- Air bubble removal: Air bubbles significantly interfere with pO2 measurements regardless of temperature 3
- Time sensitivity: pO2 is least stable at 4°C; at room temperature (22°C), pH and glucose remain stable for 90 minutes, while lactate and pCO2 are stable for 60 minutes 3
3. Technical Validation
- Daily calibration: Begin with determination of ambient barometric pressure, temperature, and relative humidity 1
- Flow/volume transducer verification: Use a calibrated 3-L syringe with agreement within 3% 1
- Gas analyzer calibration: Perform daily two-point calibrations of CO2 (0-8%) and O2 (13-21%) analyzers 1
4. Result Validation
Compare with expected values: Normal ranges 2:
Component Normal Range pH 7.35-7.45 PaCO2 35-45 mmHg PaO2 80-100 mmHg HCO3- 22-26 mEq/L O2 Saturation 95-100% Confirm significant desaturation: Significant desaturation (SpO2 change ≥5%) should be confirmed with arterial blood gases 1
Check internal consistency: Verify that pH, PaCO2, and HCO3- values are consistent with each other 4
Common Pitfalls in ABG Validation
- Relying solely on pulse oximetry: SpO2 does not detect hypercarbia or acid-base disturbances 2
- Failing to consider supplemental oxygen: This affects interpretation of oxygenation status 2
- Not accounting for temperature effects: Temperature significantly affects blood gas values 2
- Overlooking carboxyhemoglobin presence: Can falsely elevate SpO2 readings 2
- Using capillary samples inappropriately: Finger-stick capillary glucose levels may provide significantly different results compared with arterial or venous specimens when patients have low perfusion with hypotension, edema, vasopressor infusion, or mottled appearance of the skin 1
Special Considerations
- Sampling site hierarchy: Prioritize arterial or venous sampling for critically ill patients 1
- Equitable testing: Be aware of potential disparities in ABG testing among different patient populations 5
- Timing of repeat testing: Perform ABG analysis after 1-2 hours of initiating treatment and after significant changes in respiratory support 2
By following these validation procedures, clinicians can ensure accurate ABG results that properly guide clinical decision-making in critically ill patients.