Is a 20ga in the AC Essential for CTPA?

April 22, 2019

Written by Clay Smith

Spoon Feed
There was no statistical difference in inadequate vascular filling for CT pulmonary angiogram (CTPA) if the IV catheter was smaller than 20 gauge (ga) or if it was not in the antecubital fossa (AC) or forearm.  Read on for the caveats.

Why does this matter?
When pushing IV contrast under pressure for CTPA, the American College of Radiology recommends at least a 20 ga IV in the AC or forearm to accommodate the high flow rate needed and to optimize contrast timing.  But this appears to be based on expert opinion.  Might a smaller, more peripherally, or atypically located vein work?

Move over AC fossa
Of 1,500 CTPA reports retrospectively reviewed, 19.3% were technically inadequate, with more than half of those due to poor filling of the pulmonary arteries.  Patients with a 20 ga or larger IV in the AC fossa or forearm had inadequate filling 9.2% of the time; smaller or non-AC/forearm sites had poor filling 13.2% of the time.  There was no statistically significant difference (4.0%, 95% CI -1.7%-9.7%).  I would add a word of caution.  This study did not look at rate of IV extravasation, and the number of studies with a 22ga or atypically located IV was small.  The gravity flow rate of a 22ga is 35mL/min; CT contrast for PE goes in at 4-5mL/sec.  How is it possible that 10/13 (77%) with a 22ga were technically adequate?  Authors spoke with BD Medical and, “they claim that [their 22ga] can be safely used for power injection as long as the pressure is limited to 300 pounds per square inch.”  There are limits; no patients had an IV smaller than 22ga.  The number of people with hand, wrist, neck, or other non-AC/forearm IVs was small, 76 in total.  Rate of inadequate filling in a hand IV appeared higher, 7/38 (18.4%), though the 95%CI on that would be quite wide.  Only 13 people had 22ga IV catheters, and 3/13 (23.1%) had poor filling.  Generally speaking, a larger, more proximal IV is a best practice when obtaining a CTPA.  But if you can’t get other access and really need the scan, you may have success with a 22ga or non-AC/forearm location.

Source
Rethinking Intravenous Catheter Size and Location for Computed Tomography Pulmonary Angiography.  West J Emerg Med. 2019 Mar;20(2):244-249. doi: 10.5811/westjem.2018.11.40930. Epub 2019 Feb 6.

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Reviewed by Thomas Davis