Size matters


You’re faced with a dilemma – you’re putting in a cannula, you need to push fluid through quickly, and there are some difficult veins in front of you – should you put in one big one (say, an 18 gauge) or go for two smaller (20 gauge) ones?



Of course, there are a multitude of variables at play here, and if this were a real resuscitation, you’d be putting in two big ones. Out of interest though, this little study from a rather large journal has a look at fluid infusion rates between the two options.


From a purely physics point of view, the 18 gauge should give you better flow – but of course, there’s nothing quite like seeing it in a clinical situation. Looking at 18 healthy people, the 20 gauge cannula did give better flow rates, by about 5mL per minute. Interestingly enough, all the numbers they got in the study are much less than what the manufacturer says.

Of course, that extra 5mL per minute does mean an extra jab for the patient – did you really need it? Then again, if you only have two small veins, perhaps the two 20 gauge option is better than risking missing with a big cannula. Why does this happen – physics can’t be wrong. Tell us what you think below, after reading more about this curiosity here

Oh, and thanks to the Georgia State University for the physics update – excellent site


IMAGE: Horami
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