This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Post #29 and I disagree about the size of the effect, not about the direction.
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.
Correct me on the arithmetic if it is wrong; I would rather know.
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.
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.
This follows post #33 rather than contradicting it.
Safety-engineered needles are worth using if you have children or anyone else in the house, and the retraction mechanism occupies dead volume that ordinary syringes do not.
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 is the shape of it. The detail is where I would expect to be corrected.
Practical answer on dead volume across syringe, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.
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.
Happy to be corrected if someone holds better data than mine.
Building on post #38 rather than restating it.
On dead volume across syringe, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.
If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.
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.
Someone will know this better than I do and I hope they say so.
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.
Speaking only to dead volume across syringe as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.
Sharps containers are a legal requirement for disposal in several jurisdictions and a sensible precaution everywhere. A rigid sealed container is the minimum.
Worth checking against a second source before it gets quoted onward.
A request rather than an answer: could whoever has the primary source for dead volume across syringe post it? I have seen the claim three times this month and each version had lost a qualifier.
Nothing to add, except that this is the answer I would give if asked.
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.
Confirming post #51 from a second method, which matters more than confirming it from a second person.
Sharps containers are a legal requirement for disposal in several jurisdictions and a sensible precaution everywhere. A rigid sealed container is the minimum.
On balance I think that is right, and I would not bet much on it.
That reframing is the whole thing. The facts I already had.
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.
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 literature is thinner on this than the confidence in the thread implies.
On post #55 — agreed on the reasoning, with one qualification.
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.
It took me longer than it should have to see that.
Picking up post #55: that is the part I would want checked first.
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.
Filing this under things that are true until someone shows me otherwise.
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.