What changes would occur in an arterial blood gas (ABG) specimen left at room temperature for one hour?

Changes in Arterial Blood Gas Specimen Left at Room Temperature for One Hour

When an arterial blood gas specimen is left at room temperature for one hour before analysis, you would expect to see decreased pH, decreased pO2, and increased pCO2 (option A).

Explanation of Changes in ABG Specimens Over Time

Physiological Basis for Changes

When arterial blood is collected and left unanalyzed at room temperature, ongoing cellular metabolism continues within the sample, causing predictable changes:

1. pH Decreases:

   • Ongoing cellular metabolism produces CO2 and lactic acid
   • Significant decreases in pH occur after 15-30 minutes at room temperature 1, 2
   • The European Respiratory Society notes that storage for just 1 hour at room temperature causes significant decreases in pH 3

2. pO2 Decreases:

   • Oxygen continues to be consumed by cells in the sample
   • Studies show significant decreases in PaO2 from 15 minutes onward 1, 4
   • The decrease is more pronounced at room temperature compared to iced samples

3. pCO2 Increases:

   • Cellular metabolism produces CO2 which accumulates in the sample
   • Significant increases in PaCO2 are observed from 15 minutes onward 1
   • The European Respiratory Society confirms that CO2 accumulation affects pH measurement 3

Time-Dependent Changes

The magnitude of these changes increases with time:

• Within 15 minutes:

  • Initial significant changes in PaO2 and PaCO2 begin 1, 2
  • pH changes may not yet be significant

• At 30 minutes:

  • pH shows significant decreases at room temperature 1
  • PaO2 continues to decrease
  • PaCO2 continues to increase

• At 60 minutes (the scenario in question):

  • All parameters show clinically significant changes
  • pH has decreased substantially
  • PaO2 has decreased substantially
  • PaCO2 has increased substantially

Clinical Implications and Best Practices

Impact on Patient Care

These changes can lead to misdiagnosis or inappropriate treatment if not recognized:

• False respiratory acidosis diagnosis
• Underestimation of actual oxygenation status
• Incorrect assessment of ventilation status

Recommendations for ABG Handling

To avoid these pre-analytical errors:

• Analyze blood gas samples within 15 minutes of collection 1, 5
• If analysis must be delayed beyond 15 minutes, store samples on ice (0-4°C) to slow metabolic processes 1, 4
• Ensure proper heparinization of syringes to prevent clotting
• Expel air bubbles within 30 seconds of collection 4

Common Pitfalls to Avoid

• Leaving samples at room temperature for extended periods
• Using plastic syringes for long storage (can affect PCO2 and PO2) 4
• Allowing air bubbles to remain in the sample
• Failing to properly seal the sample

Conclusion

The correct answer is option A: decreased pH, decreased pO2, and increased pCO2. These changes result from ongoing cellular metabolism in the sample when left at room temperature for an hour, highlighting the importance of prompt analysis or proper storage of arterial blood gas specimens.