Fixed versus detachable needles: the trade-offs 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.
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 where I would start, not where I would stop.
Taking post #62 at face value and following it one step further.
Sharps containers are a legal requirement for disposal in several jurisdictions and a sensible precaution everywhere. A rigid sealed container is the minimum.
Post #60 and I disagree about the size of the effect, not about the direction.
I have three months of notes on fixed versus detachable needles and the honest summary is that the trend is real and the week-to-week numbers are noise. I nearly drew the opposite conclusion from the first fortnight.
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.
I am confident about the direction and much less about the magnitude.
This settles it for me, at least until somebody posts a reason it should not.
Fixed versus detachable needles has a well-known answer and a correct answer, and the interesting work is establishing that they are the same. Nobody has done that here yet.
Post #64 put the caveat in the right place and I want to underline it.
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 arithmetic in post #67 is right; the assumption feeding it is the part to check.
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.
Answering the question post #68 raises rather than the one it answers.
The claim about fixed versus detachable needles upthread is stronger than its source supports. I have read the source. The source says "associated with" and the post says "causes".
Sharps disposal: needles and syringes should be disposed in a sharps container (a rigid, puncture-resistant container). Do not put them in regular trash. Many pharmacies accept filled sharps containers.
If anyone has run this properly I would rather read that than my own guess.
Reading rather than answering, but this is the post I would point somebody at.
Post #71 describes the usual case. This is about the unusual one.
Marking my uncertainty on fixed versus detachable needles explicitly. I am confident about the direction, much less confident about the size, and not confident at all that it generalises past the case in the first post.
Adding the measurement that post #75 says would settle it.
If someone has run fixed versus detachable needles properly I would rather read that than my own reconstruction of it. Posting mine only because the thread has gone quiet.
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.
Two people in this thread mean different things by fixed versus detachable needles and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define 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.
On post #78 — agreed on the reasoning, with one qualification.
Nobody has said the unglamorous part of fixed versus detachable needles yet, so: most of the variation is explained by things that are boring to write about and easy to check.
Collapsed as off-topic by two members at trust level 3 or above
On fixed versus detachable needles: 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.
This follows post #83 rather than contradicting it.
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.
Happy to expand any of that if it is the useful part.
Worth separating two things that post #82 runs together.
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.
Adding the boring version of fixed versus detachable needles, 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.
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.