What should a technologist do with a blood gas sample that has a large air bubble and was sent to the lab on ice 30 minutes after it was drawn?

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Blood Gas Sample with Air Bubble: Proper Handling

The technologist should reject the sample because the pCO2 will be falsely decreased and the pO2 will be falsely increased due to the large air bubble in the syringe.

Impact of Air Bubbles on Blood Gas Analysis

Air bubbles in blood gas samples cause significant analytical errors through gas exchange between the bubble and blood:

  • pO2: Falsely increased by 10.8-11.2% after just 2 minutes of contact with an air bubble 1, 2
  • pCO2: Falsely decreased by 4.8% after 3 minutes of contact with an air bubble 1, 2
  • pH: Minimal changes (0.1%) that generally don't exceed clinical significance 1
  • Other parameters: Significant changes in SO2, total hemoglobin, hematocrit, sodium, and ionized calcium 1

Factors Affecting Sample Integrity

Time-Related Factors

  • The sample was drawn 30 minutes ago and kept on ice
  • While keeping samples on ice (0°C) can preserve pO2 values for up to 30 minutes 2, the presence of a large air bubble negates this benefit

Air Bubble Size and Impact

  • Even small bubbles (0.5-1% of sample volume) can cause significant errors 3
  • A "large air bubble" as described in the scenario would cause substantial interference
  • The magnitude of error increases with:
    • Duration of contact between blood and air bubble
    • Size of the air bubble
    • Agitation of the sample (such as during transport) 4

Guidelines for Blood Gas Sample Handling

According to best practices for blood gas analysis:

  1. Air bubbles should be expelled immediately after collection (within 2 minutes) 2
  2. Samples with visible air bubbles should be rejected 1
  3. Samples should be analyzed within 30 minutes if stored on ice 2
  4. Pneumatic tube transport systems can exacerbate air bubble interference 4

Decision Algorithm for Blood Gas Sample Acceptance

  1. Inspect sample for air bubbles upon receipt
  2. If large air bubbles are present:
    • Reject the sample
    • Document reason for rejection
    • Request a new sample
  3. If no air bubbles are present:
    • Verify sample was properly stored (on ice)
    • Confirm collection time is within acceptable limits
    • Proceed with analysis

Common Pitfalls to Avoid

  • Attempting to remove air bubbles at the lab: This is ineffective as gas exchange has already occurred
  • Accepting compromised samples: This leads to inaccurate results and potentially inappropriate clinical decisions
  • Failing to document rejection: Proper documentation of rejected samples is essential for quality control
  • Analyzing samples with air bubbles but flagging results: Even with warnings, clinicians may make decisions based on inaccurate values

The most recent evidence from 2024 confirms that air bubbles in blood gas syringes cause clinically significant alterations in multiple parameters, with pO2 and pCO2 being particularly vulnerable 1. Therefore, the technologist must reject this sample to prevent potentially harmful clinical decisions based on inaccurate results.

References

2
Research

Blood gas analysis: effect of air bubbles in syringe and delay in estimation.

British medical journal (Clinical research ed.), 1982

3
Research

Bubbles in samples for blood gas determinations. A potential source of error.

American journal of clinical pathology, 1976

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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