What is the recommended procedure for collecting a venous blood gas (VBG) sample?

From the Guidelines

To collect a venous blood gas (VBG) sample, it is recommended to use a 21-gauge needle, as it is associated with a lower risk of hemolysis compared to smaller gauge needles 1. When collecting a VBG sample, several factors should be considered to ensure accurate results.

• The site used for blood withdrawal is crucial, with the median cubital vein being the preferred site due to its ease of access and lower risk of complications 1.
• The preparation of the blood collection site is also important, requiring an accurate cleaning of the skin with alcohol (2-propanol) that should be allowed to evaporate to prevent contamination of the blood with residual alcohol 1.
• The position of the patient (standing, lying, sitting) can impact the hematocrit and cause fluctuations in the levels of analytes, so it is essential to consider this when collecting the sample 1.
• A tourniquet should be applied only long enough to locate a vein, ideally 60 seconds or less, to avoid prolonged stasis that may result in changes in coagulation assays 1.
• The needle should be inserted into the vein at a 15-30 degree angle, and 1-3 mL of blood should be collected in a heparinized syringe, taking care to avoid introducing air bubbles that can alter results.
• After collecting the sample, the needle should be removed, and pressure applied to the site to prevent bleeding.
• The sample should be immediately expelling any air bubbles from the syringe, capped, and gently mixed with the heparin by rolling the syringe between the palms.
• The sample should be placed on ice if analysis will be delayed more than 10 minutes and labeled with patient information and collection time before being transported to the laboratory promptly. The use of a heparinized syringe is crucial in preventing clotting that would interfere with analysis, while prompt processing minimizes metabolism by blood cells that could alter pH and gas levels 1.

From the Research

Venous Blood Gas Sample Collection Procedure

The recommended procedure for collecting a venous blood gas (VBG) sample involves several key steps:

• Using a pre-heparinized syringe to draw venous blood from the dorsal or cubital vein (peripheral) to avoid coagulation 2
• Filling the lithium and sodium heparin evacuated tubes to at least 2/3 full for accurate pH and ionized calcium results 3
• Analyzing the blood samples with an automated blood gas analyzer within a short time frame, such as 10 minutes of collection 4 or 30 minutes 2
• Considering the use of a push-pull technique via an indwelling intravenous catheter (IVC) as an alternative to direct venipuncture, which may help reduce the risk of thrombophlebitis, anxiety, and pain in patients 4

Key Considerations

When collecting a VBG sample, it is essential to:

• Use a suitable syringe and needle size, such as a 1 mL heparinised syringe with a 1-inch, 20-G needle 4
• Handle the blood samples carefully to prevent contamination and ensure accurate analysis results
• Follow established protocols and guidelines for VBG sample collection and analysis, such as those outlined in studies 3, 2, and 4

Relevant Studies

Several studies have investigated the collection and analysis of VBG samples, including:

• A study on the use of pre-heparinized syringes for VBG sample collection in healthy adults 2
• A study on the effect of heparin concentration on VBG analysis results 3
• A study comparing the push-pull technique via IVC to direct venipuncture for VBG sample collection in sick neonatal foals 4