VBG Sampling 🩸

• A venous blood gas can be used when monitoring of pCO2 and H⁺ is desirable without multiple arterial sampling.
• There is no way to correlate pO2 between venous blood gases and arterial blood gases.

• If the patient is critically ill, in shock, or hypotensive (systolic BP <90 mmHg), the initial blood gas should be arterial.

• Critically ill patients.
• Unexpected or inappropriate hypoxaemia (SpO2 <94% on air or oxygen), or any patient requiring oxygen to reach that range. Allow for transient dips to 90% or less during sleep.
• Deteriorating oxygen saturation or increasing breathlessness in previously stable hypoxaemia (for example severe COPD).
• A previously stable patient who needs a significantly increased FiO2 to hold a constant saturation.
• Risk factors for hypercapnic respiratory failure with acute breathlessness, falling saturations, drowsiness, or other CO2 retention symptoms (for example COPD or neuromuscular disease).
• Acutely breathless, or poor peripheral circulation, when a reliable oximetry signal cannot be obtained.
• Severe metabolic disturbance, for example DKA or renal failure, hypothermia (temperature <32°C), severe sepsis, shock, or altered conscious level.
• An unexpected NEWS change, or an unexpected fall in oxygen saturation of 3% or more, even if still in the target range.
• Smoke inhalation, carbon monoxide poisoning, or cyanide poisoning.

• In patients who are not at risk of metabolic acidosis, a satisfactory SpO2 plus a venous pCO2 below 6 kPa can exclude significant arterial hypoxia or hypercapnia and may avoid an ABG. BTS did not make this a formal recommendation.

• Pre-heparinised syringe
• Needle of appropriate gauge
• Well-fitting non-sterile gloves
• Tourniquet
• 70% alcohol swab
• Gauze or cotton wool, and a bandage
• Laboratory labels
• Sharps container
• Container with crushed ice if analysis is not done at the point of care

• Introduce yourself, ask the patient to state their full name, match identity to the request, explain the test, and obtain verbal consent.
• Hand hygiene, then gloves.
• Clean the site with a 70% alcohol swab for 30 seconds and allow to dry completely (30 seconds). Do not touch the cleaned site.

• Anchor the vein by placing a thumb below the venepuncture site. Insert the needle bevel up at a 30 degree angle or less.
• Peripheral venous gases are obtained by peripheral venepuncture. Fresh venepuncture is preferred.
• It is acceptable, but not ideal, to draw blood when first introducing an indwelling venous device, before connecting the cannula to intravenous fluids.
• A sample aspirated from a central line is a central venous gas, not a peripheral VBG. Specimens from central lines carry a risk of contamination or erroneous results.
• Once sufficient blood has been collected, release the tourniquet before withdrawing the needle.
• Withdraw the needle, apply gentle pressure with gauze, and ask the patient not to bend the arm. Dispose of the device immediately into a sharps container.

• Expel air bubbles, cap the syringe, and roll the specimen between the hands to mix. Cap to prevent contact with air and leaking during transport.
• Label the syringe.
• Transport immediately. Use crushed ice if analysis is not done at the point of care.

• There is no way to correlate pO2 between venous and arterial blood gases.

• Air in the sample.
• An improper quantity of heparin in the syringe, or improper mixing after blood is drawn.
• A delay in specimen transportation.

Based on