Can a Venous Blood Gas (VBG) be drawn from a Peripherally Inserted Central Catheter (PICC) line?

Venous Blood Gas Sampling from PICC Lines

Yes, venous blood gas (VBG) samples can be drawn from a peripherally inserted central catheter (PICC) line, and this practice is supported by clinical guidelines for patients with central venous access. 1, 2

Evidence Supporting VBG from PICC Lines

Venous blood sampling from central venous catheters, including PICCs, is a recognized practice in critical care settings. According to critical care guidelines, when arterial lines are temporarily or permanently unavailable, venous lines (including PICCs) can be used for blood sampling 1.

Research studies have demonstrated good correlation between central venous blood gas samples and arterial blood gas samples for key parameters:

• pH: Central venous pH correlates well with arterial pH (mean difference of approximately 0.03 units in hemodynamically stable patients) 2, 3
• PCO2: Central venous PCO2 typically runs 4-6.5 mmHg higher than arterial PCO2 4
• Bicarbonate: Minimal clinically significant difference between venous and arterial values 3

Practical Considerations When Drawing VBG from PICC Lines

1. Dedicated Lumen Considerations:

   • If using a multi-lumen PICC, it's preferable to have one lumen dedicated exclusively for parenteral nutrition (if applicable) 1
   • Blood sampling should ideally be done from a separate lumen if available

2. Proper Technique:

   • Ensure adequate discard volume to avoid contamination from infusions
   • Follow institutional protocol for blood sampling from central lines
   • Use aseptic technique to minimize infection risk

3. Interpretation Adjustments:

   • When interpreting VBG results from a PICC, clinicians can apply the following adjustments to estimate arterial values 4, 5:
     • Arterial pH ≈ venous pH + 0.05
     • Arterial PCO2 ≈ venous PCO2 - 5 mmHg

Clinical Accuracy and Limitations

The accuracy of central VBG sampling has been validated in multiple studies:

• Overall accuracy of 90% for predicting normal arterial blood gas values after appropriate adjustments 5
• High sensitivity (100%) for detecting metabolic acidosis, metabolic alkalosis, and respiratory acidosis 2
• Lower sensitivity (71%) for detecting respiratory alkalosis 2

Potential Risks and Precautions

1. Infection Risk:

   • Blood sampling from indwelling vascular catheters may increase the risk of catheter-related bloodstream infection 1
   • Strict aseptic technique is essential

2. Contamination Concerns:

   • Avoid contamination from glucose-containing fluids or other infusates 1
   • Ensure adequate discard volume is withdrawn before obtaining the sample

3. Blood Conservation:

   • Consider using a blood conservation system to minimize blood loss from frequent sampling 1

Bottom Line

Central venous blood gas sampling from PICC lines is a valid alternative to arterial blood gas sampling, particularly in patients who already have central venous access. This approach reduces the risks associated with arterial punctures while providing clinically useful information about acid-base status and ventilation when the results are properly interpreted with the known venous-arterial differences in mind.