This topic was selected because an evidence synthesis beats a textbook on it: the trials disagree, or the guidance has moved recently.
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
Meta-analysis
2021
British journal of anaesthesia
Pooling prospectively assessed children, a single general anaesthetic was associated
Randomised trial
2019
England)
In the GAS randomised trial, just under an hour of sevoflurane anaesthesia in
Cohort
2016
JAMA
Comparing 105 sibling pairs, a single anaesthetic before 36 months left no
Review
2023
Current opinion in anaesthesiology
Studies examining intraoperative blood pressure and later neurocognitive outcome
Meta-analysis
2022
JAMA network open
Across 31 studies, associations between childhood anaesthesia and neurodevelopment
Cohort
2018
Anesthesiology
In the MASK study, general intelligence was unaffected by exposure before age three
6 resolved citations behind this deck; every point above traces to one of them.
WHERE THE GUIDANCE SITS
What the guidelines and pooled evidence say
2 findings, each on the slide that follows.
British journal of anaesthesia 2021
Pooling prospectively assessed children, a single general anaesthetic was associated
Pooling prospectively assessed children, a single general anaesthetic was associated with modestly worse parent-reported behaviour scores while…
JAMA network open 2022
Across 31 studies, associations between childhood anaesthesia and neurodevelopment
Across 31 studies, associations between childhood anaesthesia and neurodevelopment differ by domain — small deficits in executive function, behaviour…
WHERE THE GUIDANCE SITS
Pooling prospectively assessed children, a single general anaesthetic was associated
Meta-analysis · British journal of anaesthesia
Pooling prospectively assessed children, a single general anaesthetic was associated with modestly worse parent-reported behaviour scores while full-scale IQ was unaffected.
Prospectively Assessed Neurodevelopmental Outcomes in Studies of Anaesthetic Neurotoxicity in Children: A Systematic Review and Meta-Analysis, British journal of anaesthesia 2021 · PMID 33250180
WHERE THE GUIDANCE SITS
Across 31 studies, associations between childhood anaesthesia and neurodevelopment
Meta-analysis · JAMA network open
Across 31 studies, associations between childhood anaesthesia and neurodevelopment differ by domain — small deficits in executive function, behaviour and academics, with cognition barely affected.
Anesthetic Exposure During Childhood and Neurodevelopmental Outcomes: A Systematic Review and Meta-analysis, JAMA network open 2022 · PMID 35708687
THE NUMBERS
Effects differ by domain, and all are small
31 studies pooled, standardised mean differences.
Every effect is a fraction of a standard deviation — real enough to mention to a parent, small enough to put in proportion.
Anesthetic Exposure During Childhood and Neurodevelopmental Outcomes: A Systematic Review and Meta-analysis, JAMA network open 2022 · PMID 35708687
WHAT THE TRIALS FOUND
In the GAS randomised trial, just under an hour of sevoflurane anaesthesia in
Randomised trial · England)
In the GAS randomised trial, just under an hour of sevoflurane anaesthesia in infancy gave a full-scale IQ at age five equivalent to awake-regional anaesthesia, with a difference of 0.23 points.
Neurodevelopmental Outcome at 5 Years of Age After General Anaesthesia or Awake-Regional Anaesthesia in Infancy (GAS): An International, Multicentre, Randomised, Controlled Equivalence Trial, Lancet (London, England) 2019 · PMID 30782342
THE NUMBERS
GAS: no IQ difference at five years
722 infants randomised to sevoflurane or awake-regional anaesthesia.
Mean IQ was equivalent between the arms, with the adjusted difference far inside the 5-point margin the trial set as clinically meaningful.
Neurodevelopmental Outcome at 5 Years of Age After General Anaesthesia or Awake-Regional Anaesthesia in Infancy (GAS): An International, Multicentre, Randomised, Controlled Equivalence Trial, Lancet (London, England) 2019 · PMID 30782342
IN PRACTICE
What the cohorts and reviews add
3 findings, each on the slide that follows.
JAMA 2016
Comparing 105 sibling pairs, a single anaesthetic before 36 months left no
Comparing 105 sibling pairs, a single anaesthetic before 36 months left no significant difference in IQ, memory, attention, executive function,…
Current opinion in anaesthesiology 2023
Studies examining intraoperative blood pressure and later neurocognitive outcome
Studies examining intraoperative blood pressure and later neurocognitive outcome have not found an association, so hypotension is not established as…
Anesthesiology 2018
In the MASK study, general intelligence was unaffected by exposure before age three
In the MASK study, general intelligence was unaffected by exposure before age three
IN PRACTICE
Comparing 105 sibling pairs, a single anaesthetic before 36 months left no
Cohort · JAMA
Comparing 105 sibling pairs, a single anaesthetic before 36 months left no significant difference in IQ, memory, attention, executive function, language or behaviour in later childhood.
Association Between a Single General Anesthesia Exposure Before Age 36 Months and Neurocognitive Outcomes in Later Childhood, JAMA 2016 · PMID 27272582
IN PRACTICE
Studies examining intraoperative blood pressure and later neurocognitive outcome
Review · Current opinion in anaesthesiology
Studies examining intraoperative blood pressure and later neurocognitive outcome have not found an association, so hypotension is not established as the mediating mechanism.
Unanswered Questions of Anesthesia Neurotoxicity in the Developing Brain, Current opinion in anaesthesiology 2023 · PMID 37552011
IN PRACTICE
In the MASK study, general intelligence was unaffected by exposure before age three
Cohort · Anesthesiology
In the MASK study, general intelligence was unaffected by exposure before age three, but children with multiple exposures showed reduced processing speed and fine motor ability that single-exposure children did not.
Neuropsychological and Behavioral Outcomes After Exposure of Young Children to Procedures Requiring General Anesthesia: The Mayo Anesthesia Safety in Kids (MASK) Study, Anesthesiology 2018 · PMID 29672337
THE NUMBERS
MASK: intelligence unaffected, some domains differ after multiple exposures
997 children tested at 8–12 or 15–20 years.
Neither difference was significant; the signal in multiply-exposed children sits in processing speed and fine motor, not IQ.
Neuropsychological and Behavioral Outcomes After Exposure of Young Children to Procedures Requiring General Anesthesia: The Mayo Anesthesia Safety in Kids (MASK) Study, Anesthesiology 2018 · PMID 29672337
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
Pooling prospectively assessed children, a single general anaesthetic was associated with modestly worse parent-reported behaviour scores while full-scale IQ was unaffected.
2
2
Across 31 studies, associations between childhood anaesthesia and neurodevelopment differ by domain — small deficits in executive function, behaviour and academics, with cognition barely affected.
3
3
In the GAS randomised trial, just under an hour of sevoflurane anaesthesia in infancy gave a full-scale IQ at age five equivalent to awake-regional anaesthesia, with a difference of 0.23 points.
4
4
Comparing 105 sibling pairs, a single anaesthetic before 36 months left no significant difference in IQ, memory, attention, executive function, language or behaviour in later childhood.
5
5
In the MASK study, general intelligence was unaffected by exposure before age three, but children with multiple exposures showed reduced processing speed and fine motor ability that single-exposure children did not.
The oral-boards stem on the next slide puts these into one scenario.
KEY TAKEAWAYS
What to carry into the next case
Pooling prospectively assessed children, a single general anaesthetic was associated
British journal of anaesthesia 2021
In the GAS randomised trial, just under an hour of sevoflurane anaesthesia in
England) 2019
Comparing 105 sibling pairs, a single anaesthetic before 36 months left no
JAMA 2016
Studies examining intraoperative blood pressure and later neurocognitive outcome
Current opinion in anaesthesiology 2023
Pooling prospectively assessed children, a single general anaesthetic was associated
Questions I'll ask you in the room
Walk me through your setup for this before we start.
What are you watching on the monitor that would tell you this is going wrong?
What is your first move if it does?
What would you want ready in the room before induction?
Oral boards stem
The mother of a healthy 14-month-old presenting for inguinal hernia repair has read that anaesthesia harms developing brains and asks you directly whether the operation should wait.
Board questions
1. In the GAS randomised trial, infants received either just under an hour of sevoflurane general anaesthesia or awake-regional anaesthesia. What was the full-scale IQ result at age five, and how large was the difference between the groups?
Show answer
Full-scale IQ at age five after just under an hour of sevoflurane anaesthesia in infancy was equivalent to awake-regional anaesthesia, with a difference of 0.23 points.
A 0.23-point IQ difference at five years is the number to remember when a parent asks about a short single anaesthetic in infancy.
Neurodevelopmental Outcome at 5 Years of Age After General Anaesthesia or Awake-Regional Anaesthesia in Infancy (GAS): An International, Multicentre, Randomised, Controlled Equivalence Trial, Lancet (London, England) 2019 · PMID 30782342
2. In the MASK study of children exposed to general anaesthesia before age three, the findings differed between children with one exposure and children with several. Describe what was and was not affected in each group.
Show answer
General intelligence was unaffected by exposure before age three overall. Children with multiple exposures showed reduced processing speed and fine motor ability, and single-exposure children did not show those reductions.
MASK points the concern at repeated exposure and at specific domains — processing speed and fine motor — rather than at global intelligence.
Neuropsychological and Behavioral Outcomes After Exposure of Young Children to Procedures Requiring General Anesthesia: The Mayo Anesthesia Safety in Kids (MASK) Study, Anesthesiology 2018 · PMID 29672337
3. A parent asks whether a single general anaesthetic will affect her child's development. Drawing on the pooled prospectively assessed studies of anaesthetic neurotoxicity in children, what two different outcome domains should you distinguish in your answer, and what did the pooled data show for each?
Show answer
Distinguish behaviour from intelligence. Pooling prospectively assessed children, a single general anaesthetic was associated with modestly worse parent-reported behaviour scores, while full-scale IQ was unaffected. Note that the behaviour finding is an association and the measure is parent-reported.
Splitting behaviour from IQ is what lets you give a parent an honest answer instead of a reassuring one or a frightening one.
Prospectively Assessed Neurodevelopmental Outcomes in Studies of Anaesthetic Neurotoxicity in Children: A Systematic Review and Meta-Analysis, British journal of anaesthesia 2021 · PMID 33250180
4. Intraoperative hypotension is often proposed as the mechanism linking early childhood anaesthesia to later neurocognitive problems. What have studies of intraoperative blood pressure and later neurocognitive outcome actually shown, and what does that mean for calling hypotension the mechanism?
Show answer
Studies examining intraoperative blood pressure and later neurocognitive outcome have not found an association, so hypotension is not established as the mediating mechanism. The absence of an association means the proposed mechanism is unsupported, not that some other mechanism has been proven instead.
It is fair to say we have not established hypotension as the mediator — it is not fair to substitute a different mechanism we like better.
Unanswered Questions of Anesthesia Neurotoxicity in the Developing Brain, Current opinion in anaesthesiology 2023 · PMID 37552011
The bottom linePooling prospectively assessed children, a single general anaesthetic was associated
Sources
[1] Prospectively Assessed Neurodevelopmental Outcomes in Studies of Anaesthetic Neurotoxicity in Children: A Systematic Review and Meta-Analysis, British journal of anaesthesia 2021 · PMID 33250180 open
[2] Neurodevelopmental Outcome at 5 Years of Age After General Anaesthesia or Awake-Regional Anaesthesia in Infancy (GAS): An International, Multicentre, Randomised, Controlled Equivalence Trial, Lancet (London, England) 2019 · PMID 30782342 open
[3] Association Between a Single General Anesthesia Exposure Before Age 36 Months and Neurocognitive Outcomes in Later Childhood, JAMA 2016 · PMID 27272582 open
[4] Unanswered Questions of Anesthesia Neurotoxicity in the Developing Brain, Current opinion in anaesthesiology 2023 · PMID 37552011 open
[5] Anesthetic Exposure During Childhood and Neurodevelopmental Outcomes: A Systematic Review and Meta-analysis, JAMA network open 2022 · PMID 35708687 open
[6] Neuropsychological and Behavioral Outcomes After Exposure of Young Children to Procedures Requiring General Anesthesia: The Mayo Anesthesia Safety in Kids (MASK) Study, Anesthesiology 2018 · PMID 29672337 open