Worth separating two things that post #59 runs together.
I would rather this thread reach "we do not know" about Dead volume across syringe than reach a confident answer that nobody can support when asked.
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Devices · Syringes & needles · continued
Follow-up: Dead volume across syringe and needle combinations posts 61–90
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.
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.
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aliquot_line, post #16: Drawing through a wider needle and injecting through a thinner one is a reasonable approach for a viscous preparation and pointless for an aqueous one. The claim is narrower than it sounds, and deliberately so. Go to post
The quoted dead-volume figures for common configurations vary between manufacturers and the ordering is stable: fixed needle least, luer with hub more, luer with filter needle most.
That is one dataset and I would not build a rule on it.
n.ekstrom, post #2: The quoted dead-volume figures for common configurations vary between manufacturers and the ordering is stable: fixed needle least, luer with hub more, luer with filter needle most. That much is documented. The rest is how I have interpreted it. Go to post
Adding a note of thanks rather than an opinion. I did not know most of that.
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.
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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.
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Everything in post #63 holds. The case it does not cover is the one I have.
Two claims get bundled together under Dead volume across syringe and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.
Almost every disagreement in threads like this one dissolves once you say which of the two you are making.
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e.roos, post #9: Coming back to post #8, because the follow-up matters more than the original answer. 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. Go to post
Narrowing post #67, because the general version has more than one answer.
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.
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.
Marking that as an opinion rather than a finding.
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Adding the measurement that post #67 says would settle it.
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.
This is the sort of thing that ought to be settled and apparently is not.
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n.rowntree, post #58: Answering the question post #54 raises rather than the one it answers. Coring the stopper is a real phenomenon with repeated entries at the same point and blunt needles. Varying the entry point slightly and using a fresh needle prevents it. Go to post
Adding the measurement that post #70 says would settle it.
Whatever the answer on Dead volume across syringe turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, invite the correction.
Needle length for subcutaneous delivery is a question about tissue depth and injection angle together. Short needles at ninety degrees and longer ones at an angle reach comparable depths.
Noting that I have skin in this question and have tried to discount for it.
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bench_peak, post #69: 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. Marking that as an opinion rather than a finding. Go to post
If your calculated volume is under two graduations, choose a lower concentration rather than trying to read between marks. Precision comes from the preparation, not the eye.
Reusing a needle blunts it and there is no benefit to offset that. The second injection with the same needle is the one people describe as painful.
That holds for the case as described. Change the assumptions and it may not.
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Building on post #75 rather than restating it.
Filter needles are for drawing from glass ampoules where particulate is a real risk. For a stoppered vial they add dead volume in exchange for very little.
That has held every time I have looked, which is not the same as always.
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Worth separating two things that post #76 runs together.
Coring the stopper is a real phenomenon with repeated entries at the same point and blunt needles. Varying the entry point slightly and using a fresh needle prevents it.
The answer changed when I changed how I was measuring, which was informative.
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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.
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k.marchand, post #17: Building on post #16 rather than restating it. 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. Go to post
Reading this Dead volume across syringe thread as someone who came in with a fixed view: the third and seventh replies moved me and the confident ones did not.
Building on post #81 rather than restating it.
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.
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Noted, and thank you for writing it out rather than summarising it.
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k.kuusela, post #55: Needle length for subcutaneous delivery is a question about tissue depth and injection angle together. Short needles at ninety degrees and longer ones at an angle reach comparable depths. It is worth stating the boring hypothesis before the interesting one. Go to post
Fixed-needle insulin syringes have the least dead volume of any common configuration. At small doses that difference is a measurable fraction of what you meant to deliver.
Post #86 and I disagree about the size of the effect, not about the direction.
A detachable luer needle plus hub can retain enough volume to matter. Whether it matters to you depends on your dose, and the arithmetic is worth doing once.
The literature is thinner on this than the confidence in the thread implies.
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Taking post #86 at face value and following it one step further.
I would be cautious about generalising from the Dead volume across syringe example above. It is a good example. It is one example.
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footnote_entry, post #67: Everything in post #63 holds. The case it does not cover is the one I have. Two claims get bundled together under Dead volume across syringe and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not. Almost every disagreement in threads like this… Go to post
Picking up post #89: that is the part I would want checked first.
My understanding of Dead volume across syringe is a few years old and may have been superseded. If it has been, I would genuinely like to know rather than keep repeating it.