On the subject in the title: Dead volume across syringe and needle combinations Working notes rather than a conclusion.
Something about dead volume across syringe does not reconcile and I would like a second pair of eyes before I decide which half is wrong.
Two sources, both reputable, giving figures that cannot both be right unless they are measuring different quantities. My suspicion is that they are, and I cannot see how.
Taking post #2 at face value and following it one step further.
What would change my mind on dead volume across syringe is a second dataset collected by someone with no stake in the first. Until then I hold it loosely and I would rather say so than pretend to more.
The opening post and I disagree about the size of the effect, not about the direction.
The useful distinction on dead volume across syringe is between what was measured and what was inferred from it. Both end up in the same sentence and only one of them has error bars.
That is the distinction I keep failing to hold on to. Written down now.
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.
I have seen it go both ways, which is why I hedge.
Worth separating two things that post #4 runs together.
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.
Answering the question post #8 raises rather than the one it answers.
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.
Worth separating two things that post #7 runs together.
On dead volume across syringe: the maintained page in the documentation commons covers the general case with citations and a review date, which is more reliable than any reply here including this one.
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.
I have separated what I observed from what I concluded, which does not always happen.
Insulin syringe graduations: U-100 syringes are marked in units where 100 units = 1 mL. Always confirm your syringe is U-100. Confusion between insulin units and milligrams is the most common syringe error.
That is the version I would defend. It is not the version I started with.
Following, with nothing to contribute beyond having asked the same thing elsewhere.
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.
I would treat the number as indicative rather than as a measurement.
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.
Reporting the observation and leaving the explanation open deliberately.
Confirming post #16 from a second method, which matters more than confirming it from a second person.
Adding the boring version of dead volume across syringe, because the interesting version keeps getting posted and the boring one is usually right.
Check the ordinary explanations, in order, and stop when one of them accounts for what you are seeing. Most of the time the second one does.
Following this. I have the same question and no better information than the first post.
On post #18 — agreed on the reasoning, with one qualification.
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.
If it helps: the failure mode here is usually boring rather than dramatic.
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.
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.
Worth separating two things that post #22 runs together.
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.
The evidence for this is thinner than the way I have phrased it suggests.
I would be cautious about generalising from the dead volume across syringe example above. It is a good example. It is one example.
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.
On dead volume across syringe, I would rather understate and be corrected upward than overstate and be quoted. That is a house style here and it is a good one.