July 14, 2020
Siting an IV cannula for serial blood sampling Minimize

Siting an IV cannula for serial blood sampling

Most tests require the insertion of one IV cannula through which provocative agents are administered and/or periodic blood samples drawn. A large vein in the antecubital fossa is the preferred insertion site. Occasionally separate infusion and sampling cannulas are required. Butterfly needles are useful for single samples, but are not recommended where multiple samples are to be taken.


  • Local anaesthetic cream (EMLA cream or patch) for children
  • Largest cannula that is practicable; in children this will be a size 22g or 25g, in adults a size 18g
  • Saline for skin cleansing
  • Vials of IV saline for flushing the cannula

IV cannula insertion

  1. Local anaesthetic cream is applied for a minimum of one hour (in children)
  2. Site cleaned with sterile water
  3. Cannula inserted and taped in cross-over fashion with 1 cm Micropore tape
  4. Cannula flushed with 2 mL normal saline

Sampling from IV cannula

All samples are drawn using aseptic technique. Gloves should be worn for protection.

When sampling from a cannula, it is imperative that sufficient void volume be removed before the blood sample for analysis is collected, otherwise the sample will be diluted and spurious results obtained. 0.5 to 1 mL should be withdrawn prior to drawing of the blood sample if a standard T-piece is being used - in infants and young children this can be replaced if volume considerations are critical. Cannulas should be flushed with saline, unless patency difficulties are experienced.


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