Dead volume across syringe and needle combinations posts 61–81
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Dead volume across syringe has been discussed here with more heat than it deserves, mostly because two definitions have been in play the whole time.
I read post #62 twice before replying, because I had assumed the opposite.
The most useful thing anyone has posted about dead volume across syringe in this category was a table of what had been measured and by whom. That is what I would want again.
Needle length: typical lengths for subcutaneous injection are 4-6 mm (short), 8 mm (standard), or 10-12 mm (longer). Longer needles are needed for deeper tissue or if you have abdominal adiposity.
The short answer was in the first line; everything after is the working.
Needle gauge: smaller numbers (30G) are finer and less painful. Larger numbers (25G) are courser. For subcutaneous injection, 27-30G is typical. Finer needles take longer to draw up but hurt less.
None of the above is medical advice and I am not qualified to give any.
Post #64 is right about the mechanism and I think understates the practical bit.
Dead volume: residual liquid in the hub and needle after withdrawal. Typical residual is 0.01 to 0.02 mL for an insulin syringe with a fixed needle. Accounting for it matters if precision matters.
Source for the dead volume across syringe figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.
Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.
Where I part company with post #66, and it is a narrow parting.
Check what the graduations actually say rather than what you expect. A syringe marked in units and one marked in millilitres look similar at a glance and are not the same instrument.
Written in the hope of being told what I have missed.
Syringe barrel size: common sizes are 0.3 mL, 0.5 mL, and 1.0 mL. Smaller barrels are more legible for small doses. Larger barrels hold larger volumes. Choose based on your dose.
That is the honest state of it as of this week.
Taking post #69 at face value and following it one step further.
Fixed versus detachable needles: insulin syringes usually have fixed needles (no dead volume loss to the hub). Luer-lock syringes use detachable needles (more dead volume). Fixed needles are preferred for small doses.
The reasoning is more useful than the number, which is why I have shown it.
Collapsed as off-topic by two members at trust level 3 or above
Barrel size determines resolution and nothing else. A 0.3 mL barrel and a 1 mL barrel deliver the same volume equally well; the smaller one lets you see what you are delivering.
That is what the documentation says. What happens in practice is usually close.
U-100 means the barrel is graduated for a solution containing one hundred units of insulin per millilitre. For anything that is not insulin, the units are simply hundredths of a millilitre.
Marking that as an opinion rather than a finding.
Adding a small correction to the dead volume across syringe summary above rather than a disagreement with it. The substance holds; one of the figures is out by a factor that matters.
Dead volume across syringe is a good example of a question where the honest answer is boring and the interesting answers are unsupported. I would go with boring.
U-100 means the barrel is graduated for a solution containing one hundred units of insulin per millilitre. For anything that is not insulin, the units are simply hundredths of a millilitre.
This topic was referenced in
- Filter needles: when they help and what they cost youDevices › Syringes & needles · 50 replies
- Reading a syringe in poor light, and how to avoid needing toDevices › Syringes & needles · 2 replies
- Follow-up: Dead volume across syringe and needle combinationsDevices › Syringes & needles · 98 replies
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