Blood gas syringe

OVERVIEW

• special syringes are used for blood gas analysis

USE

• collection of a blood sample for accurate analysis by a blood gas machine

DESCRIPTION

• usually pre-packaged and disposable
• contain a small amount of lyophilised heparin (e.g. Li heparin)
• usually plastic (previously glass and required heparin to be added)
• have a cap to prevent contact with gases in the air
• should be left at room temperature and analysed within 30 minutes (previously glass syringes were kept chilled on ice to prevent metabolism and allow delays in analysis)
• usually 1 or 3 mL sizes

Various designs

• needles of different length and gauge built into the syringe or are needle-less
• safety covers for needles when they retract or a foam pad to inject the sharp into before removing the syringe
• Luer lock tips
• ‘self filling’ plungers that move when arterial pulsation is detected or plungers that are retractable to a desired sample volume creating a chamber for blood to enter
• gradations showing volumes on the side

METHOD OF USE

• Blood is drawn into the syringe, using a needle that enters a vessel or from an intravascular cannula (e.g. arterial sampling line)
• analysis is performed as soon as possible by a blood gas machine

COMPLICATIONS

Sources of inaccuracy associated with sample collection:

• Excessive delay to processing (allows continued metabolism by the erythrocytes and reduces pH and pO2 and increases pCO2)
• Air bubbles (cause a fall in pCO2 and an increase in pO2)
• Severe anaemia (the capacity for buffering oxygen may be reduced)
• Leucocyte larceny (severe leucocytosis causes metabolic decrease in pO2 and increase in pCO2 and cell lysis with increase K+)
• Failure to interpret that a sample is venous rather than arterial and vice versa
• Excess haemolysis causing artefactually increased potassium
• Inadequate mixing of syringe before analysis (falsely low Hb due to RBCs settling out)
• Sample take from a crushed or ischemic limb

OTHER INFORMATION

• Not all syringes are compatible with all blood gas machines and point of care devices