Trypanophobes Rejoice! Big IVs Hurt No More Than Little Ones

April 2, 2024

Written by Nick Zelt

Spoon Feed
This single centre RCT investigated the link between IV cannula diameter and how painful it will be to insert. 18G cannulas were not more painful nor more difficult to place than 20G cannulas across the spectrum of experience levels. Pain and insertion success rates being equal, patients are better off with cannulas that can accommodate higher flow rates.

Death to the comically large needle, you need not fear it.
Few patients pass through our doors without being punctured or skewered by some sort of needle. We accept this as a necessary evil, but since we’ve already failed at “do no harm,” we are duty bound to extract maximal value from the cannulas we insert (think fluid flow rates). Logically, one might assume that a larger needle would be more painful and more difficult to insert. But medicine isn’t always logical.

These authors conducted a single-blinded, comparative RCT in an Australian ED. Adult patients were block randomized to receive either a 20G or 18G IV cannula. 181 patients were blinded (literally, with blackout glasses) to the cannula used. The primary outcomes were pain experienced by the patient and procedural difficulty experienced by the clinician, both assessed on visual analog scales (VAS).

The overall success rate for cannula insertion on first try or within the first 3 tries was not significantly different. Mean pain stores were also similar, 3.61 for 20G and 3.84 for 18G, mean difference of 0.23 (95%CI 0.56–1.02, p = 0.57). This lack of difference held true across all experience levels (medical student to registrar), though overall pain was less in those with more experience. Similarly, procedural difficulty was also not significantly different between groups.

How will this change my practice?
It seems that in Australia doctors place the majority of IVs. It’s not common for me to insert an IV unless all others have failed; then I place one under ultrasound guidance. Also, the preferred cannulation site was the antecubital fossa, while most of my patients end up with IVs in their hands. All the same, this paper will make me less sheepish to always reach for the larger cannula and advocate for others to do the same.

Source
Spiced RCT: Success and Pain Associated with Intravenous Cannulation in the Emergency Department Randomized Controlled Trial. J Emerg Med. 2024;66(2):57-63. doi:10.1016/j.jemermed.2023.10.008.