Scott Segal Professor of Anesthesiology

Chair, Department of Anesthesiology Tufts University School of Medicine

Fetal brain toxicity & anesthetic agents: yet another reason to avoid

general anesthesia?

Behavioral teratogenicity

� Enduring behavioral changes without gross structural defects

� Common anesthetics can cause long-term behavioral abnormalities

NMDA antagonism and brain injury

Science 1999; 283:70-74

Ikonomidou et al. 1999

� Seven-day-old rats ¡ Intra-peritoneal vehicle or dizocilpine (MK801),

NMDA antagonist ¡ Brains stained

÷ TUNEL (fragmented DNA, sign of apoptosis) ÷ Silver (cell death)

TUNEL staining

Ikonomidou, Science 1999; 283:70-74

Ikonomidou et al. 1999

Ikonomidou et al. 1999

� Drug given lasted 4-6 hr � Same effect seen with PCP, ketamine � Effects sensitive to gestational age or post-

natal age ¡ Rats synaptogenesis peaks at 7 days age ¡ Corresponds to third trimester and postnatal

period in humans

� Rats exposed to “triple cocktail”: N2O, midazolam, isoflurane

� Day 7 (peak synaptogenesis), 6 hr anesthetic � Sacrificed for histology or studied later for

learning ability

J Neuroscience 2003

Jevtovic-Todorovic 2003

Control Silver Caspase 3

Morris water maze

Jevtovic-Todorovic 2003

Radial arm maze

Jevtovic-Todorovic 2003

Other anesthetics

� NMDA antagonists ¡ Ketamine ¡ N2O

� GABAA agonists ¡ Midazolam, diazepam ¡ Pentobarbital, thiopental ¡ Propofol ¡ Isoflurane, sevoflurane ¡ Ethanol

Mechanisms

� NMDA ¡ Glutamate signaling important for synapto-

genesis, NMDA antagonists block

� GABA ¡ Increases chloride influx, cell protection in adult ¡ Causes chloride efflux, calcium influx in

developing brain ¡ Unclear how apoptosis triggered

Criticism (1)

� Large doses, prolonged exposures � Post-natal neurodevelopment in rats � No surgical stimulation accompanies the

anesthetics � Hemodynamics, respiratory status, glucose

not been uniformly observed or controlled ¡ GA causes hypoglycemia in rats ¡ Hypoglycemia impairs immature brain

development

Loepke AW, McGowan FX, Soriano SG. Anesth Analg 2008 (June)

Criticism (2)

� Neuroplasticity implies regeneration of neurons lost to apoptosis is likely

� Some effects are only observed when exposure occurs on certain developmental days and not others

� Species specificity ¡ Mice, rabbits, piglets, sheep intact after isoflurane

4-6 hr ¡ Most behavioral consequences have only been

observed in rats

Loepke AW, McGowan FX, Soriano SG. Anesth Analg 2008 (June)

Criticism (3)

� Human brain development slower, would require 2 wk exposure to be equivalent

� Human experience with neonatal anesthesia spans decades and does not demonstrate significant neurotoxicity

� Some anesthetics (e.g. xenon), are NMDA antagonists but cause no toxicity ¡ May even be protective

Loepke AW, McGowan FX, Soriano SG. Anesth Analg 2008 (June)

Responses to criticism

� Doses are sub-anesthetic in species studied ¡ Anesthetic dose ketamine 5 mg/kg humans, 80 mg/

kg mouse ¡ Isoflurane MAC 1.15% humans, 2.26% in mouse

� Brain slices, cell culture confirm results ¡ No blood flow, hemodynamic, glucose issues

�  ISF studies in other species experiments flawed ¡ Must look within hrs for apoptosis ¡ Staining methods critical

� Non-human primates show effects in <8 hr (ethanol) or 5.5 hr (ketamine)

Jevtovic-Todorovic V., Olney, JW. Anesth Analg 2008 (June)

What about human record of safety?

� Ethanol clearly causes human degeneration ¡ But unrecognized for centuries ¡ Only appreciated 2° craniofacial abnormalities

� Rapid recovery from anesthesia is not reassuring ¡ Seen in rat, guinea pig, monkey models as well ¡ Little investigation of long-term cognitive effects

Jevtovic-Todorovic V., Olney, JW. Anesth Analg 2008 (June)

� Guinea pigs: longer gestation, more brain development in utero, larger animal

� Exposed to “triple cocktail”: 75% N2O, midazolam (1 mg/kg IM), isoflurane (0.55%) vs. fentanyl (“sham”) vs. control

� 4 hr anesthetic � Fetal (2 hr post anesthesia) or neonatal

(35-40 d post) brains studied for histology

Brain Pathology 2008

Rizzi 2008

Rizzi 2008

Rizzi 2008

Brain toxicity in animal models

� Not confined to apoptosis ¡ Neurogenesis, microgliosis ¡ Dendritic spine formation, synaptic function

� Not confined to post-natal exposure ¡ Guinea pigs: peak effect in 2nd trimester ¡ Rhesus monkeys: 24 hr ketamine in utero ¡ Rats 2nd trimester: behaviorally abnormal as

adults (Palanisamy et al. 2011)

� Timed pregnant rats (day 14) exposed to 1.4% isoflurane or 100% O2 for 4 h

� Offspring subjected to multiple behavioral tests at 8 weeks (young adult)

� Exposed adults abnormal in radial arm maze and elevated plus maze ¡ Impaired spatial working memory, reduced

anxiety

Anesthesiology 2011 (Mar); 114: 521–8

Brain toxicity in animal models

� Not confined to rats ¡ Mice, guinea pigs ¡ Nonhuman primates (ketamine in rhesus monkey)

Neurotoxicology and Teratology 33 (2011) 220–230

� Rhesus monkeys exposed/unexposed to ketamine 24 hr ¡ Day 5-6 postnatal ¡ Returned to mothers, weaned @ 7 months ¡ Began standardized cognitive training

Paule et al., 2011

Human data

Anesthesiology 2009 (April); 110:796 – 804

Wilder et al.

� Olmsted county, Minnesota � 593 children undergoing GA less than age 4

¡ Halothane 88%, N2O 91% ¡ No other drugs >10%

� 4764 children with no GA � Incidence of learning disabilities K-12

¡ Reading, writing, or mathematics ¡ >1.75 SD below IQ-predicted standard score

Wilder et al.

Limitations of Wilder et al.

� Surgical procedures, diseases uncontrolled ¡ Authors: may be impossible ¡ Authors: maybe treating (surgically) is better for

development than not treating � Definition of learning disability nonstandard

¡ Authors: standard in MN � Hypoxia, hyperoxia may confound results

¡ Authors: hypoxia not linked to LD (retinopathy treatment), hyperoxia likely modest (70% N2O)

Human epidemiology

� Hernia repair < 3 yrs (N=383) vs. controls (N=5050) (DiMaggio 2009) ¡ 2.3 fold greater prevalence behavioral problem or

developmental delay

� Danish cohort hernia repair in infancy (N=2689) vs. controls (Hansen 2011) ¡ No difference in test scores grade 9 ¡ More exposed children never took tests

Twin, sibling studies

� Children exposed to 1, 2, or 3 anesthetics vs. controls (DiMaggio 2011) ¡ RR developmental/behavioral disorders

increased from 1.1 to 2.9 to 4.0 ¡ No difference between matched sibling pairs

� Monozygotic twins, only one exposed age <3 yr (N=1143 pairs) (Bartels 2009) ¡ Lower test scores age 12 in exposed group ¡ No difference between matched exposed vs.

unexposed twin pairs

Obstetric anesthesia

Anesthesiology 2009 (Aug); 111:302–10

Sprung et al, 2009

� Olmsted county, Minnesota � 5320 children born 1976 –1982 and

remaining in the community at age 5 � Cesarean delivery 497 (9.3%)

¡ General anesthesia N=193 ¡ Regional anesthesia N=304

Sprung et al., 2009

� General anesthetics used (NMDA and GABA) ¡ Total 193 patients ¡ Intravenous agents

÷ Sodium thiopental 189 ÷ Ketamine 2

¡ Inhalational agents ÷ Enflurane 15 ÷ Halothane 105 ÷ Isoflurane 6 ÷ Methoxyflurane 42 ÷ Nitrous oxide 191

CS anesthetic effect on LD

HR 0.88 (0.59–1.31)

HR 0.64 (0.44–0.92) P=0.017 vs. VD

20.8%

19.4%

15.4%

CS anesthetic effect on LD

� Controlling for anesthesia in child from birth to age 4: no change in results

� Controlling for emergency CS: no change � Controlling for other covariates of LD differing

among delivery modes: no change ¡ Induction ¡ Maternal age ¡ Maternal education ¡ Birthweight, sex ¡ Labor complications

Sprung et al: conclusions and limitations

� CS under GA does not alter LD risk vs. VD � CS under regional appears safer than VD,

perhaps because stress response is blocked � Many limitations

¡ Retrospective birth cohort design ¡ Lower CS rate than today ¡ Outdated GA agents ¡ No assessment of labor analgesia

Analgesia for vaginal delivery

� Olmstead county database 1976-82 � 1495/4684 received neuraxial analgesia

Anesth Analg 2011;112:1424–31

Flick et al. 2011

b = adj for gest age, birthweight, Apgar, surgery < age 5, maternal education c = adj for “b” + details L&D (induction, duration, forceps, inhalation anes, etc.)

Neurotoxicity: the future

� Preclinical ¡ Mechanisms (Ca++ homeostasis) ¡ Critical periods ¡ Protective strategies (!-2 agonists)

� Clinical ¡ Prospective observation (PANDA), RCTs? (GAS trial) ¡ Very difficult to design (Thomas et al., A&A, 2011)

÷ Age, type of surgery ÷ Anesthetics (RA vs. GA, sedation) ÷ Outcomes (preschool, school, adolescence, adult)

Neonatal anesthetic neurotoxicity

� Animal studies convincing and worrisome � Mechanisms appear relatively clear

¡ Is it true in human brain? ¡ Can adverse effects be blocked?

� Human data on apoptosis is nonexistent � Human epidemiology rare but concerning � Prudent in 2011 to reserve GA for

emergencies