Small patient size and sarcopenia are additional factors that increase potential risk for local anesthetic systemic toxicity (LAST).
THE EVIDENCE
What each source contributes, and how strong it is
Study design first — a cohort and a randomised trial do not carry the same weight.
Design
Year
Journal
What it found
Other
2017
Regional anesthesia and pain medic
Small size, sarcopenia increase LAST risk
Other
2022
The American journal of emergency
Ultrasound, Aspiration, Minimal Dose Reduce LAST Risk
Other
2018
Local and regional anesthesia
LAST causes isolated cardiovascular disturbance sometimes
3 resolved citations behind this deck; every point above traces to one of them.
THE NUMBERS
Four in ten cases do not follow the textbook progression
The classic march from tinnitus to seizure to arrest is the majority, not the rule.
A patient who becomes unstable late, or who arrests with no preceding neurologic signs, is still LAST. Waiting for the classic march is how the diagnosis gets missed.
Di Gregorio et al., Reg Anesth Pain Med 2010 · PMID 20301824
IN PRACTICE
What the cohorts and reviews add
3 findings, each on the slide that follows.
Regional anesthesia and pain medicine 2018
Small size, sarcopenia increase LAST risk
Small patient size and sarcopenia are additional factors that increase potential risk for local anesthetic systemic toxicity (LAST).
The American journal of emergency medicine 2022
Ultrasound, Aspiration, Minimal Dose Reduce LAST Risk
Using ultrasound guidance, aspiration before injection
Local and regional anesthesia 2018
LAST causes isolated cardiovascular disturbance sometimes
LAST can present with isolated cardiovascular disturbance in one-fifth of reported cases.
IN PRACTICE
Small size, sarcopenia increase LAST risk
Other · Regional anesthesia and pain medic
Small patient size and sarcopenia are additional factors that increase potential risk for local anesthetic systemic toxicity (LAST).
The Third American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Local Anesthetic Systemic Toxicity: Executive Summary 2017, Regional anesthesia and pain medicine 2018 · PMID 29356773
IN PRACTICE
Ultrasound, Aspiration, Minimal Dose Reduce LAST Risk
Other · The American journal of emergency
Using ultrasound guidance, aspiration before injection, and using the minimal local anesthetic dose needed can reduce the risk of LAST.
Local anesthetic systemic toxicity: A narrative review for emergency clinicians, The American journal of emergency medicine 2022 · PMID 35777259
IN PRACTICE
LAST causes isolated cardiovascular disturbance sometimes
Other · Local and regional anesthesia
LAST can present with isolated cardiovascular disturbance in one-fifth of reported cases.
Local anesthetic systemic toxicity: current perspectives, Local and regional anesthesia 2018 · PMID 30122981
IN THE ROOM
What this changes about the next case
Colour is the strength of the evidence behind each step, not the urgency.
1
1
Small patient size and sarcopenia are additional factors that increase potential risk for local anesthetic systemic toxicity (LAST).
2
2
Using ultrasound guidance, aspiration before injection, and using the minimal local anesthetic dose needed can reduce the risk of LAST.
3
3
LAST can present with isolated cardiovascular disturbance in one-fifth of reported cases.
The oral-boards stem on the next slide puts these into one scenario.
KEY TAKEAWAYS
What to carry into the next case
Small size, sarcopenia increase LAST risk
Regional anesthesia and pain medicine 2018
Ultrasound, Aspiration, Minimal Dose Reduce LAST Risk
The American journal of emergency medicine 2022
LAST causes isolated cardiovascular disturbance sometimes
Local and regional anesthesia 2018
Use minimal LA doses, aspirate, consider patient size/sarcopenia, and recognize potential isolated cardiac signs to prevent LAST.
Questions I'll ask you in the room
What is the primary mechanism underlying CNS toxicity from local anesthetics?
How does lipid solubility relate to the potential for systemic toxicity?
What are the key clinical signs differentiating cardiac versus CNS toxicity?
Besides epinephrine, what other factors influence the rate of systemic absorption?
Oral boards stem
Five minutes after an interscalene block with 20 mL of 0.5% ropivacaine, the patient reports perioral numbness and tinnitus, then becomes confused.
Board questions
1. In a review of 93 published cases of local anaesthetic systemic toxicity from 1979 to 2009, what proportion followed the classic progression from neurologic prodrome to seizure to cardiovascular collapse?
About 60%
About 95%
About 30%
Essentially all of them
Show answer
A. About 60%
Sixty percent followed the classic pattern. In the rest, symptoms were substantially delayed after injection, or involved only cardiovascular compromise with no CNS signs at all. Waiting for the textbook march is how the diagnosis gets missed.
Di Gregorio et al., Clinical presentation of local anesthetic systemic toxicity: a review of published cases 1979-2009, Reg Anesth Pain Med 2010 · PMID 20301824
2. Forty minutes after an uneventful interscalene block with ropivacaine, a patient becomes progressively hypotensive and bradycardic on the ward. There were no neurologic symptoms at any point. Your colleague says this cannot be LAST because it is too late and there was no seizure. How do you answer, using the published case series?
Show answer
Each feature on its own is within the reported spectrum. In the 1979-2009 review of 93 cases, roughly 40% did not follow the classic picture: symptoms were either substantially delayed after injection, or consisted only of cardiovascular compromise with no CNS toxicity. So neither the delay nor the absence of a seizure is evidence against LAST, and the LAST protocol including lipid emulsion stays on the table.
Timing and the absence of seizure do not exclude LAST. Anchoring on the classic sequence is the specific error this case series was written to correct.
Di Gregorio et al., Clinical presentation of local anesthetic systemic toxicity: a review of published cases 1979-2009, Reg Anesth Pain Med 2010 · PMID 20301824
3. What is the main methodological limitation of the 1979-2009 LAST case review, and what does that mean for how you use its numbers when teaching?
Show answer
It is a retrospective review of published case reports, so it cannot establish incidence, outcomes, or the comparative efficacy of any treatment. It can only characterise the clinical spectrum of reported cases. The authors themselves argue this makes the case for a prospective registry. So the 60/40 split is a statement about what LAST can look like, not about how often LAST happens or what works.
Publication bias runs through every number in a case-report series. Use it to widen your differential, never to quote a rate.
Di Gregorio et al., Clinical presentation of local anesthetic systemic toxicity: a review of published cases 1979-2009, Reg Anesth Pain Med 2010 · PMID 20301824
The bottom lineUse minimal LA doses, aspirate, consider patient size/sarcopenia, and recognize potential isolated cardiac signs to prevent LAST.
Sources
[1] The Third American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Local Anesthetic Systemic Toxicity: Executive Summary 2017, Regional anesthesia and pain medicine 2018 · PMID 29356773 open
[2] Local anesthetic systemic toxicity: A narrative review for emergency clinicians, The American journal of emergency medicine 2022 · PMID 35777259 open
[3] Local anesthetic systemic toxicity: current perspectives, Local and regional anesthesia 2018 · PMID 30122981 open
[4] Di Gregorio et al., Reg Anesth Pain Med 2010 · PMID 20301824 open