The effect of sevourane anesthesia for dental procedure on neurodevelopment in children: a prospective, equivalence, controlled trial

Background Dental procedures under general anesthesia (DGA) was found to improve the oral health-related quality of children's life. However, some parents and pediatricians expressed concern about the neurotoxicity of general anesthesia. The purpose of this trial was to investigate whether DGA in children has an adverse effect on neurodevelopment. In this prospective, assessor-masked, controlled, equivalence trial, we recruited 340 children younger than 7 years who were undergoing caries treatment between Feb 1, 2019, and Aug 31, 2019, without factors affecting neurodevelopment. They received either sevourane-based general anesthesia or awake-local anesthesia. The Wechsler Preschool and Primary Scale of Intelligence-Fourth Edition Chinese version was used to evaluate the neurodevelopment of children at six months after surgery, and the Full-Scale IQ (FSIQ) was selected as the primary outcome. Predene the 95% CI of a difference in means within ve (1/3 SD) as the equivalence margin. parents considering delaying surgery due to developmental disorders and medical risks. The longer-term neurodevelopmental outcomes after anesthesia exposure need to be assessed in the future.

Trial Registry (number ChiCTR1800015216), and the ethics committee approval of the Stomatological Hospital of Chongqing Medical University was obtained (number CQHS-IRB-2018-01).

Participants
Inclusion criteria included healthy children less than 7 years old scheduled for caries treatment (treated more than 6 teeth and expected duration of surgery more than 1 h). Exclusion criteria were any contraindication for anesthesia, previous exposure to general anesthesia, moderate to severe preterm infants (gestational age no more than 33 weeks), very low birth weight infant (birth weight less than 1500g), any known neurological injury or developmental issues, other known diseases that might affect neurodevelopment, epileptic, deaf-mute or blind, and any reason that might make follow-up di cult. Eligible children were recruited in the Department of Pediatric Dentistry or Anesthesiology of the Stomatological Hospital of Chongqing Medical University. During the research, children were excluded if they suffered brain injuries, underwent any other surgery, or failed to complete all procedures as protocol.

Anesthesia
The awake-local anesthesia group received the local in ltration anesthesia after the behavior induction. Children under 4 years old were given 2% lidocaine hydrochloride injection (5ml: 0.1g, Southwest Pharmaceutical Co.; SFDA no.H50020038), with the total dose no more than 4 mg/Kg. Children aged 4 years and older were given 4% articaine hydrochloride and epinephrine tartrate injection (1.7ml: 68mg, Produits Dentaires Pierre Rolland; SFDA no.H20140732), with the maximum dosage not exceeding 5 mg/Kg.
The general anesthesia group only received sevo urane (120ml, Shanghai Hengrui Pharmaceutical Co.; SFDA no.H20070172) for induction and maintenance. After induction with 5 L / min oxygen and 8% sevo urane through the mask, the anesthetists chose and inserted the modi ed rst-generation single-lumen laryngeal mask airway of the appropriate model. Anesthetists adjusted sevo urane concentration during maintenance according to vital signs and Bispectral Index (the majority between 40 and 60 for the suitable depth of anesthesia), mostly 2.5% to 3% with a 2 L / min mixture of air and oxygen. In the whole process, the patients retained spontaneous breathing, and PetCO 2 was usually maintained within 35 to 45 mmHg. Supplemental opioids, benzodiazepines, and other general anesthetics were not allowed, but local anesthetics were permitted to provide analgesia with the same dose as the local anesthesia group. There was postanesthesia care for 2 h after surgery. They were allowed to leave the hospital after the modi ed Aldrete score reached 10 points.

Data collection and measure
Before the operation, demographic data, pregnancy and birth details, and family structure were collected. During surgery, anesthetists recorded vital signs and perioperative adverse events. The patients were followed up by telephone on the day of surgery and the rst day after surgery.
At six months after surgery, the WPPSI-IV (CN) was used to assess the neurodevelopment for two groups of children. It was to be done within one month after half a year after surgery. All children individually completed one-to-one with the quali ed assessor. It took approximately 1.5 h for each child to complete the assessment. Parents were asked if children had been found physical abnormalities since caries treatment, and brief physical and neurological examinations were done for patients.
We selected FSIQ, Verbal Comprehension Index (VCI), Visual-Spatial Index (VSI), Fluid Reasoning Index (FRI), Working Memory Index (WMI), and Processing Speed Index (PSI) from the composite score of WPPSI-IV (CN) as the evaluation indicators.

Statistical analysis
The hypothesis was that the FSIQ score is equivalent in children who have received general anesthesia or local anesthesia for caries treatment at six months after surgery. The equivalence margin was de ned as ve (1/3 SD), and a two one-sided test was performed with the 0.025 level of signi cance. Equivalence was prede ned as the 95% CI of difference between the mean of the FSIQ score within -5 to +5. Secondary outcomes for this analysis were selected VCI, VSI, FRI, WMI, and PSI. They also have a mean of 100 and a standard deviation of 15. It is reasonable to assume that their equivalence margins are ve. All CIs are two-sided.
The statistical analysis plan prespeci ed the age at evaluation (< 4 years old or ≥ 4 years old) as a subgroup analysis. Several predictor variables of primary outcome used in the regression model included anesthesia group, sex, gestational age at birth, birthweight, past medical histories of children, mother's abnormalities during pregnancy, mother's education, maternal age at delivery, perioperative adverse events, age at evaluation, and postoperative developmental disorders. In the general anesthesia group, the duration of sevo urane exposure was used as a predictor variable and grouped (less than 120 min, 120 to 180 min, and more than 180 min) to observe the effect of different anesthesia duration on the primary outcome. All analyses were done in SPSS (version 25).

Trial process
Between Feb 1, 2019, and Aug 31, 2019, 1681 children were screened for eligibility, and 340 patients were recruited. After three withdrawal of consent by parents (pre-surgery), the intent-to-treat analysis included 168 children in the general anesthesia group and 169 children in the local anesthesia group. 31 participants with surgery being canceled or protocol violations were excluded, and 150 patients in the general anesthesia completed the surgery and 156 in the local anesthesia group.
Follow-up was from Aug 1, 2019, to Mar 22, 2020. 28 families were lost to follow-up or withdrew consent, and one child was injured by fall from height. In the per-protocol analysis, the WPPSI-IV (CN) was complete for 129 in the general anesthesia group and 144 in the local anesthesia group ( gure).

Demographic data at baseline and non-scale measurement after surgery
Demographic data at baseline and anesthesia details are shown in table 1. There were 63 boys (49%) in the general anesthesia group and 77 boys (53%) in the local anesthesia group. The age at surgery was from 2.5 to 6.5 years old. Among all participants, 9 mothers had mild abnormalities during pregnancy, and 12 children had a past medical history. The median duration of sevo urane use was 130 min (110 to 160). The only adverse event during the perioperative period in the general anesthesia group was related to respiratory complications (two cases of slight laryngospasm), and one case of the local anesthetic adverse reaction occurred in the local anesthesia group.
Non-scale measurement at six months after surgery are shown in table 2. There were 16 children less than 4 years old in the general anesthesia group and 9 children in the local anesthesia group. After surgery, no child had a diagnosis of febrile convulsion, epileptic seizure, or cerebral palsy, nor did they fail to complete WPPSI-IV (CN) due to developmental issues or behavioral disorders. The neurological examinations of all children were normal.
Overall results of scale measurement The scores of FSIQ and main indexes (VCI, VSI, FRI, WMI, and PSI) in the WPPSI-IV (CN) of the two groups were shown in table 3. For the FSIQ score, the mean was 103·12 (SD 8.94) in the general anesthesia group and 103·58 (8.40) in the local anesthesia group. We noted evidence for equivalence between groups in means (mean difference for local anesthesia minus general anesthesia 0.46, 95% CI -2.35 to 1.61). There was also evidence for equivalence in the scores of VCI, VSI, FRI, WMI, and PSI between groups. The upper and lower limits of the 95% CIs were well inside the prespeci ed equivalence margin of ve in all analyses.

Subgroup analysis and predictor variables analysis of scale measurement
In the subgroup analysis, the FSIQ score between groups was equivalent in the age group less than 4 years old. It was the same in the age group older than 4 years. There was no signi cant difference between the two age groups in the general anesthesia group and the local anesthesia group (p> 0.05). For the secondary outcomes, in the age subgroup of younger than 4 years, the VSI and WMI were not found to be equivalent between groups; in the age subgroup of older than 4 years, the VSI was not equivalent (table 4).
In the regression analysis, it was found that the anesthesia group, sex, preterm, birthweight, past medical histories of children, mother's pregnancy disease, maternal age at delivery, perioperative adverse events, and age at evaluation could not signi cantly affect the primary outcome (p> 0.05). Only the signi cance level of maternal education was less than 0.05 (b= 0.02), which could affect the FSIQ score. In the general anesthesia group, the duration of sevo urane exposure did not signi cantly affect the primary outcome (p= 0.86), and there was no signi cant difference between different anesthesia durations (p= 0.21).
Besides, we also analyzed the delivery mode and family structure and found that the cesarean section and second child could not signi cantly affect the primary outcome (p> 0.05).

Discussion
We noted evidence for equivalence between general anesthesia and local anesthesia in children for caries treatment in terms of the FSIQ in WPPSI-IV (CN) measured at six months after surgery. Equivalence was also shown in the VCI, VSI, FRI, WMI, and PSI, because the 95% CIs of the differences in means fell inside a third of an SD, well within our prede ned margins of clinical equivalence. Local in ltration anesthesia in children is known to be safe and effective 16 .
Therefore, it can be reasonably considered that children receiving prolonged DGA with sevo urane alone had no adverse changes in neurocognitive development at six months after surgery.
The WPPSI-IV (CN) is a well-proven method for evaluating development, and the FSIQ score as the overall result is an appropriate evaluation indicator.
Intelligence that covers multiple cognitive areas (memory, reasoning, spatial ability, executive ability, and processing speed) is deemed to be a relatively steady and constant trait of young children, and intellectual development in early childhood can predict and evaluate the future intelligence 17 . The WPPSI-IV (CN) includes ve main indexes, which are mainly used to evaluate the ability of knowledge expression and spoken language, visual-spatial information processing and vision-action coordination, uid intelligence and inductive reasoning, visual working memory and attention, and cognitive exibility and visual scan. Consequently, we use the WPPSI-IV (CN), a validated, internationally recognized, and standardized measurement tool to assess the neurocognitive development and general intellectual of children. There are high-quality norms in China and high clinical validity. It is extensive academic literature and application experience. It has neuropsychological evaluation characteristics and can provide composite scores representing the intellectual function of speci ed cognitive domains (verbal IQ, performance IQ, and processing velocity) and an overall score for FSIQ 18 . There are previous studies assessing children exposed to anesthesia with medical and school records 19,20 . However, individually measured cognitive abilities are more sensitive than the performance of group-tested academic skills 21 .
From 3rd trimester to 24 months of age is the peak synaptogenesis of neurons, which is the most vulnerable to potential toxins. So many studies are directed at infants and children under 2 to 3 years old. However, brain development in children is dynamic and on-going. And infants undergoing surgery at a very young age are more likely to have underlying diseases, which may confuse the effects of general anesthesia exposure on neurodevelopmental outcomes. 17 Therefore, we selected preschool children as the research object to observe whether the neurodevelopment in children after the peak synaptogenesis of neurons is susceptible to general anesthesia.
The combination of disease and surgery made previous retrospective studies di cult to assess the independent effect of anesthesia exposure 20,22 . In the PANDA study, more than one anesthetic was used 13 . The GAS trial was dominated by male infants (over 80%), and the duration of surgery was less than 1 h (median 54 min) 10,11 . This trial only included healthy children who had no potential factors or disease that in uenced neurodevelopment. For the surgery, just caries treatment with little painful noxious stimulation, and almost no effect on the internal environment of the body was selected. The general anesthesia group used a sevo urane-only anesthetic. It was to reduce the interference of the confounding factors of the disease, surgery, and the drug interaction of multiple general anesthetics. Considering that behavioral differences after general anesthesia in animal models may be owing to sex differences 23 , the ratio of male and female recruited was approximately 1:1. The duration of general anesthesia was in the range of 1 to 4 h. The aim is to assess the effects of prolonged (nontransient) general anesthesia exposure on neurodevelopment in children (not just boys).
At present, there is no direct correlation between anesthesia and neurotoxicity of cognitive or behavioral sequelae in children 24 . Recent ndings suggest that the anesthetic neurotoxicity is not a major contributor to adverse neurodevelopmental outcomes for most healthy children who require surgery. Biological, environmental, and social factors are far greater import 25 . In the subgroup analysis, we found that although a few indicators in the secondary outcomes were not equivalent between groups, the scores in the general anesthesia group were not all lower than those in the local anesthesia group. Therefore, this difference may be caused by environmental or other factors, rather than general anesthesia. We also found that the mother's education had an impact on the neurodevelopmental outcome in children. The higher the mother's education, the better comprehensive neurocognitive ability on children, but the in uence is not great.
Inconsistent with other research conclusions 14,23 , we did not nd that premature, the duration of sevo urane exposure, and the age of children had a signi cant effect on neurocognitive outcome. It was similar in maternal abnormalities during pregnancy and past medical histories of children. Because after the screening, moderate to severe preterm infants were excluded, and these participants just had the mild disease in the past. They were relatively healthy.
Awake-local anesthesia inevitably has a failure rate. It was unavoidable that children may refuse surgery or change to general anesthesia due to dental anxiety. If all children were analyzed on an intention-to-treat basis, the results obtained would be more conservative and dilute the potential effect of general anesthesia, making the differences between groups more di cult to detect. To minimize this bias and ensure the reliability of the results, we analyzed mainly on a per-protocol basis.
Our trial has several limitations. The local anesthesia group could not compare the duration of surgery and anesthesia with the general anesthesia group.
Although the two groups of children have similar severity of caries, almost all children with multiple caries could not complete all treatments at once with local anesthesia. It was usually required multiple visits so that the duration could not be counted. Therefore, the advantage of DGA is to provide convenient and e cient treatment. The general anesthesia group used a sevo urane-only anesthetic without other general anesthetics. Thus, our trial cannot be generalized to practice in all pediatric surgery, and cannot elucidate possible outcomes if other agents are added.
Another limitation is that the children were recruited mainly in Chongqing, Southwest China. The ndings may be in uenced by the differences from region and economy. At present we have only evaluated the participants at six months after surgery. To avoid the practice effect, after the recommended interval (one year), the subsequent evaluation of participants can be more accurately describe long-term neurocognitive outcomes after DGA.

Conclusion
This trial, being congruent with data from several previous clinical studies, found no evidence that prolonged exposure to DGA only with sevo urane in relatively healthy preschool children causes adverse neurodevelopmental outcomes (including language, reasoning, memory, and vision-action) and neurological de cits at six months after surgery. These ndings should reassure pediatricians and parents considering delaying surgery due to developmental disorders and medical risks. The longer-term neurodevelopmental outcomes after anesthesia exposure need to be assessed in the future.    Figure 1 Trial pro le