Anesthetic Neurotoxicity vs. the Developing Brain

Every year, millions of infants receive anesthesia for life-saving procedures. But what if those same drugs are reshaping the brain being built behind their eyes?

By Terrence Wu

By Kaplanclinic.com

Imagine you are a parent. Your three-month-old needs open-heart surgery. The surgeon tells you the procedure is straightforward and the odds are good. Then you ask a single question that catches everyone in the room off guard: “What will the anesthesia do to her brain?”

The doctor pauses. Not because the answer is bad — but because, after more than 20 years of research, millions of dollars in funding, and hundreds of published studies, nobody can give you a complete answer.

This is the great crisis of anesthetic neurotoxicity in pediatric medicine, not the question or discussion of it. An official alert was released by the FDA in 2016 stating that exposure to anesthetic drugs on a recurring or prolonged basis in children younger than age three may have implications for cognitive and behavioral development, and the anesthetics still must be used. The reason for the continued use of anesthetics is that the alternative for a child needing surgery without an anesthetic would most likely be death.

“We are caught between two unacceptable options: accepting the risk of neurotoxicity, or accepting the risk of untreated disease. The only way out is better science.” — Dr. Mary Ellen McCann, Boston Children’s Hospital.

Does General Anesthesia Before the Age of 3 Cause Lasting Cognitive Harm?

Is anesthesia dangerous? That is a very general and non-specific statement that gets you nowhere. The appropriate question to ask is: when a drug used as an anesthesia is introduced, when the brain is being actively formed at its highest rates of synaptic growth, do these result in demonstrable long-term deficits in cognition, behavior, or even in brain structure?

That is wholly different from the question as to whether or not anesthesia is dangerous to the adult brain or causes reversible adverse effects. The question of neurotoxicity specifically concerns the immature brain and the possibility of anesthetics interfering in the most critical period of neuron formation.

Two molecular mechanisms are implicated in most research:

• GABA-A receptors upregulation — medications such as propofol, isoflurane, and sevoflurane enhance the action of the principal inhibitory transmitter. In the maturing nervous system, GABA acts as the main inhibitory transmitter, which is essential for building synapses. Stopping its activity inappropriately might impair the construction process, which cannot be corrected.
• NMDA receptor blockade — Drugs like ketamine target a receptor that plays a critical role in learning and memory. The development of brain cells needs NMDA receptor function to determine which synaptic connections to retain or eliminate.

The Three Research Groups Leading This Field

Progress in this field has been driven by a small number of dedicated teams. Three stand out for their consistent output, methodological rigor, and direct influence on clinical practice.

Dr. Mary Ellen McCann · Pediatric Anesthesiologist & Lead Investigator Boston Children’s Hospital / Harvard Medical School

Who led the GAS Trial, which is the largest study of its type, comparing anesthesia for babies less than 60 weeks? The GAS Trial examined the outcome for the babies from birth to five years of age. The results of the Gas Trial indicate that babies given anesthesia appear to have no impairment to cognition at 5 years. From the Gas Trial, it is indicated that maybe what we are measuring for these infants is not a good indicator of their outcome. This study has significance in knowing how general and regional anesthesia contribute to outcomes for the infant.

Dr. Vesna Jevtovic-Todorovic · Neuroscientist & Anesthesiologist University of California, Davis School of Medicine

Dr. Vesna Jevtovic-Todorovic, actually the first person to study the effect of the medications people generally use to put them to sleep, can actually harm the brains of young rodents. Her 2003 paper was a landmark study that was crucial for the initial field of research and caught the attention of the FDA (Food and Drug Administration, an organization responsible for the safety of drugs to humans). Today, she is working to discover what it is about the medications that causes harm to the animals’ brains, and to determine how cell death occurs in the brain. Currently, she is investigating the cell death mechanisms that cause an anesthetic-induced cell death and the strategies employed to protect the brain.

Dr. Lena Sun & The SmartTots Consortium · Clinical Researcher & Multi-Institution Research Network Columbia University Irving Medical Center / FDA-Funded SmartTots

PANDA Study (Pediatric Anesthesia and NeuroDevelopment Assessment) — headed up this study that compared siblings (one given GA under 36 months and one not) and showed no significant difference in IQ at 8–15 years. Shape and coordination of SmartTots public-private partnership with the largest research agenda on this issue.

What the Evidence Actually Shows

Human research in this field has produced genuinely mixed results — not because the science is poor, but because the problem is structured in difficulty.

Studies suggesting possible risk:

• Large population studies (Wilder et al., Mayo Clinic, 2009) found that children with multiple anesthetic exposures before age 4 had a higher rate of learning disabilities
• Some cohort studies report mild attention-related differences and slightly lower language scores in children with prolonged or repeated exposures
• Animal studies across rodents and primates consistently show neuroapoptosis and behavioral deficits, most pronounced with ketamine and isoflurane

Studies showing no significant harm:

• The GAS Trial (McCann, 2019): No significant difference in neurodevelopmental scores at age 5 between infants receiving general vs. regional anesthesia for hernia repair
• PANDA Study (Sun, 2016): Sibling-controlled design found no IQ difference between children who had a single general anesthetic before age 36 months and their unexposed siblings
• MASK Study (Mayo Clinic, 2019): Single exposure showed no difference; multiple exposures associated with subtle processing speed differences but not IQ

The problem with understanding these results, though, is that children who need surgery are different from kids who don’t. This is because they were either born with birth defects and/or got seriously ill, all of which can influence the developing brain and make it difficult to know if the anesthesia or the sickness is influencing brain development. This is essentially the question scientist trying to answer within the topic.

The problem, however, is that kids who require surgery are different than the general population. This means that these kids often come with their own complications that can influence the developing brain (being premature, birth defects, etc). Therefore, it is difficult to know if the anesthetic agent itself is affecting the developing brain or if it is the complications that are affecting the developing brain. This is what can be hard in analyzing the results of these studies.

The Gaps: What We Still Do Not Know

Despite significant investment and decades of work, critical knowledge gaps remain. These are not gaps from lack of effort — they reflect genuine structural barriers in the science.

1. Long-term outcomes beyond age 5 are largely unknown. Most trials measured outcomes at age 2 and age 5. But complex cognitive functions — executive function, abstract reasoning, emotional regulation — don’t fully emerge until adolescence. We may simply be measuring too early.
2. Repeated exposures remain understudied in controlled settings. Most randomized trials involve single exposures. But the children most likely to be harmed — those with chronic conditions requiring multiple surgeries — are the hardest to study ethically.
3. Individual genetic vulnerability is not yet mapped. Some children may carry variants that make their developing neurons more sensitive to GABA-enhancing or NMDA-blocking agents. Without biomarkers, it's not possible to identify who is most at risk before exposure.
4. No neuroprotective agent has been validated in humans. Lab research has found several candidate compounds (lithium, melatonin, dexmedetomidine) that reduce anesthetic-induced apoptosis in animals, but none have yet been tested in a controlled human trial.
5. Brain imaging is not yet sensitive enough. Current MRI and EEG techniques can detect large structural changes but may miss subtle connectivity differences that correlate with cognitive outcomes.

“The absence of evidence is not evidence of absence. A test that is not sensitive enough to detect harm will always report no harm — even if harm is occurring.” — Adapted from Dr. Andrew Davidson, Royal Children’s Hospital, Melbourne

The Immediate Risk: Local Anesthetic Systemic Toxicity (LAST)

While the neurotoxicity debate focuses on effects unfolding over years, anesthesia also carries a rare but life-threatening risk: Local Anesthetic Systemic Toxicity (LAST). LAST happens when local anesthetic drugs enter the bloodstream at toxic concentrations — through accidental intravascular injection, excessive dosing, or even impaired metabolism.

LAST: Symptoms and Consequences

• Sudden onset of seizures or cardiac arrhythmias — can occur within seconds of exposure.
• Cardiac arrest requiring immediate resuscitation — documented in pediatric cases worldwide
• Severe acute brain injury from oxygen deprivation
• Death if intravenous lipid emulsion (the antidote) is not administered within minutes
• Risk is higher in infants due to lower body weight and less mature drug metabolism.

LAST is now managed through mandatory weight-based dosing protocols, real-time ultrasound guidance during nerve blocks, and universal availability of lipid emulsion rescue therapy. While rare, LAST demonstrates that anesthetic risk is not limited to hypothetical long-term effects — it can be acute, immediate, and lethal.

What Clinicians Are Already Doing

The medical community has not waited for definitive research before acting. These risk-reduction strategies are now standard practice in pediatric anesthesiology:

1. Delaying elective procedures in children under 3 whenever medically feasible
2. Minimizing anesthesia duration through optimized surgical technique and team coordination
3. Lowest effective dosing using weight-based calculations and continuous monitoring
4. Regional anesthesia, where possible — nerve blocks and spinal techniques to replace or reduce general anesthesia
5. Multi-drug combinations — lower doses of multiple agents rather than high doses of any single drug
6. Dexmedetomidine as an adjunct — an alpha-2 agonist with possible neuroprotective properties, increasingly used in pediatric cases.

The Path Forward

Closing the knowledge gap requires a coordinated research agenda that no single institution can execute alone. The SmartTots consortium — a public-private partnership between the FDA, International Anesthesia Research Society, and dozens of academic medical centers — represents the most organized global effort currently underway. Their priorities include:

• Adolescent follow-up of existing cohorts — extending the GAS, PANDA, and MASK studies through puberty to capture late-emerging cognitive functions
• Genetic vulnerability mapping — genome-wide association studies to identify variants that increase sensitivity to anesthetic neurotoxicity
• Advanced neuroimaging — diffusion tensor imaging and resting-state fMRI to detect subtle connectivity changes invisible to standard cognitive tests
• Human neuroprotective trials — translating the most promising animal findings (dexmedetomidine, lithium, melatonin) into Phase I/II human safety trials
• Better ethical frameworks — research designs that generate meaningful data while fully respecting the rights and safety of pediatric participants

Conclusion

Go back to that parent. Their three-month-old needs surgery. They’re asking what anesthesia will do to their child’s brain.

Here is the honest answer that the best available science supports today: a single short exposure to general anesthesia in an otherwise healthy infant does not appear to cause measurable cognitive harm by age 5. But we do not have strong data beyond age 5. We do not fully understand repeated exposures. We cannot yet identify the children who may be genetically vulnerable. And we have no validated neuroprotective agent to offer them.

That is not a reassuring answer. It is an honest one — and in medicine, honesty is the foundation of every meaningful advance.

For the children who need surgery now — and there will be millions of them — the answer is to proceed with the best current protocols, the lowest necessary doses, and the shortest possible exposures. And to keep demanding better science.

Core Takeaways:

• The specific concern: general anesthesia before age 3 may disrupt synaptogenesis via GABA and NMDA receptor interference — but human evidence is mixed
• The GAS Trial and PANDA Study found no significant IQ harm from a single short exposure; repeated or prolonged exposures remain more uncertain.
• Three leading research groups: McCann (Boston Children’s/GAS Trial), Jevtovic-Todorovic (UC Davis/animal mechanisms), Sun & SmartTots (Columbia/PANDA)
• Key gaps: no long-term data past age 5, no validated neuroprotective agent in humans, no genetic vulnerability map
• LAST demonstrates that anesthetic risk can also be immediate and fatal — managed through strict modern protocols
• The SmartTots consortium is the most coordinated global effort to close the knowledge gap.

About the Author

My name is Terrence Wu, and I'm a Grade 9 student with an interest in anesthesiology. I research and sometimes write about anesthesia to develop my understanding of topics that will shape my future career — and to share what I learn with others who are just as curious. This article will be one of many that will be written.

If you’re a physician, anesthesiologist, or researcher in this space, and are open to a conversation. I would love for an opportunity to connect and talk.