Questions · Popliteal Sciatic Nerve Block
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Recall — derived from a kept point
One hundred patients were randomised to a single-injection or a triple-injection subparaneural popliteal sciatic block, with an identical 15 ml of local anaesthetic in both. Give the success rates and total anaesthesia-related times, then say which technique you would teach a junior and why.
Answer: Both techniques succeeded in 92% of patients, and total anaesthesia-related time — performance plus onset — was 17.1 to 19.7 minutes in both. The triple-injection technique had a shorter onset (12.5 versus 15.8 minutes) but needed three needle passes instead of one and a longer needling time. I would teach the single injection: for the same success rate and the same total time to a usable block, it involves a third of the needle passes and a shorter needling time. Be careful how you argue that, though. This trial found procedural discomfort and the incidence of paraesthesia similar between the groups, so fewer passes is an argument from the count of passes and from needling time, not from any harm this study demonstrated. And the reason usually given for expecting one injection to suffice — that once local anaesthetic is under the paraneurium the sheath itself distributes it circumferentially — is the authors' stated hypothesis going in, not something the trial measured.
The endpoint that matters is total anaesthesia-related time, not onset time. A technique that starts working three minutes sooner but takes longer to perform has not saved anyone anything.
Source claim: In 100 patients randomised to single-injection or triple-injection subparaneural popliteal sciatic nerve block with 15 ml of local anaesthetic, both techniques gave a 92% success rate and comparable total anaesthesia-related times of 17.1 to 19.7 minutes, with the single-injection technique requiring fewer needle passes (1 versus 3) and a shorter needling time (3.0 versus 4.0 minutes) and the triple-injection technique giving a shorter onset time (12.5 versus 15.8 minutes); performance time, procedural discomfort and the incidence of paraesthesia (14-20%) were similar between the two groups. The authors' stated hypothesis was that multiple injections are not required when local anaesthetic is deposited under the paraneurium because the paraneurium entraps the local anaesthetic molecules, ensuring circumferential spread around the nerve.
Tiyaprasertkul W et al., A Randomized Comparison Between Single- and Triple-Injection Subparaneural Popliteal Sciatic Nerve Block, Reg Anesth Pain Med 2015
recall · CA-1 · phrased by llm
Sixty-eight patients received an ultrasound-guided subparaneural popliteal sciatic block with 30 ml of local anaesthetic either at the neural bifurcation or proximal to it, at the common sciatic trunk. The success rates were 85% to 88% and total anaesthesia-related times 23.4 to 26.0 minutes, with no significant difference between them. Why should you not report this trial as showing the two levels are equivalent?
Answer: Because the trial was too small to exclude a difference that would matter. The authors say so themselves: on the 95% confidence intervals they could not rule out an intergroup difference of up to 19% in success rate and up to 7.83 minutes in total anaesthesia-related time. A 19% difference in success is clinically large, so "no significant difference" here means the trial did not detect one, not that one does not exist. Sonographic neural swelling was also seen in five subjects across the two groups, and two patients had residual numbness at one week which had resolved by one month.
Absence of a significant difference in a 68-patient trial is a statement about the trial's power. Read the width of the confidence interval before you call two techniques equivalent — the authors of this one did exactly that in print.
Source claim: In 68 patients randomised to bifurcation or prebifurcation subparaneural popliteal sciatic nerve block, success rates were 85% to 88% and total anaesthesia-related times 23.4 to 26.0 minutes with no significant difference, but the 95% confidence intervals could not exclude an intergroup difference of 19% in success rate and 7.83 minutes in total anaesthesia-related time; sonographic neural swelling was detected in 5 subjects across the two groups (2 prebifurcation and 3 bifurcation), in all of whom the needle was withdrawn and the injection completed uneventfully, and follow-up one week after surgery revealed 2 patients with residual numbness, which had resolved by one month.
Tran QH et al., A randomized comparison between bifurcation and prebifurcation subparaneural popliteal sciatic nerve blocks, Anesth Analg 2013
recall · CA-1 · phrased by llm
This randomized trial found that adding ___ mg magnesium sulfate to ropivacaine for popliteal sciatic nerve block in bunion correction surgery shortened sensory block onset to 9.2 minutes and prolonged duration to 18.2 hours compared to saline.
Answer: 200
This randomized trial found that adding 200 mg magnesium sulfate to ropivacaine for popliteal sciatic nerve block in bunion correction surgery shortened sensory block onset to 9.2 minutes and prolonged duration to 18.2 hours compared to saline.
Ropivacaine and magnesium sulfate in sciatic nerve block at the popliteal level: randomized double-blind study · PMID 39480231
recall · CA-1 · phrased by derived
This meta-analysis found that continuous popliteal sciatic nerve block lowers VAS pain scores at 24 and ___ hours postoperatively compared to single-injection, but carries a 13.9% risk of catheter drug leakage.
Answer: 48
This meta-analysis found that continuous popliteal sciatic nerve block lowers VAS pain scores at 24 and 48 hours postoperatively compared to single-injection, but carries a 13.9% risk of catheter drug leakage.
The efficacy and safety of continuous versus single-injection popliteal sciatic nerve block in outpatient foot and ankle surgery: a systematic review and meta-analysis · PMID 31601208
recall · CA-1 · phrased by derived
This randomised trial found that for forefoot surgery using ___ ml of ropivacaine 0.5% with multimodal analgesia, a sciatic nerve block at the popliteal crease does not provide a longer duration of analgesia than an ankle block.
Answer: 30
This randomised trial found that for forefoot surgery using 30 ml of ropivacaine 0.5% with multimodal analgesia, a sciatic nerve block at the popliteal crease does not provide a longer duration of analgesia than an ankle block.
Duration of analgesia after forefoot surgery compared between an ankle and a sciatic nerve block at the popliteal crease: A randomised controlled single-blinded trial · PMID 37972929
recall · CA-1 · phrased by derived
The point with one number taken out. No model wrote any of this: the stem is the sentence you reviewed, minus a digit, and the paper it came from is named beneath it.
Open prompts
Walk me through your setup for this before we start.
open · CA-1 · phrased by derived
What are you watching on the monitor that would tell you this is going wrong?
open · CA-1 · phrased by derived
What is your first move if it does?
open · CA-1 · phrased by derived
What would you want ready in the room before induction?
open · CA-1 · phrased by derived
Questions only — nothing here asserts anything, which is why a model is allowed to phrase them. Where no model was reachable these are the level defaults.