Objective: analysing the association between exposure to anaesthesia and surgery before age 4 years and long-term academic and cognitive performance.
Design: retrospective cohort study.
Setting: Study of national scope. Swedish population born between 1973 and 1993.
Study population: children that had a single exposure to anaesthesia for surgery before age 4 years and no subsequent hospitalizations until age 16 years. The total number of children that underwent surgery in the period under study was 121 498, of which 59 714 were excluded and 61 784 were eligible, and finally 33 514 were included in the surgery cohort (SC). The control cohort (CC) consisted of 159 619 unexposed children matched 5:1 by sex, month of birth, county of residence at birth and maternal parity. Data were recovered from the Swedish Medical Birth Register and the Swedish Patient Register. Two more groups were analysed: patients with two or more surgeries (secondary cohort, 3640 patients) and patients in the SC that required in-hospital care for any reason between ages 4 and 16 years (tertiary cohort, 54 637 patients).
The exclusion criteria were patients born in or that eventually moved to counties without register coverage, that died before 16 years, at high risk of cognitive impairment by nature of the disease for which surgery was indicated, or with one of several predetermined diagnoses such as cancer or major malformation.
Outcome measurement: the primary outcome was academic performance, assessed by the mean school grades at age 16 years and intelligence test (IT) scores from the military conscription review. The means were normalised to allow for comparison and the final effect was calculated as the difference between the means of the two cohorts expressed as percentage unit change. The authors performed logistic regression to analyse the association of having grades below the 10th percentile, no recorded school grades at age 16 and no available IT scores with other covariates such as age at surgery, type of surgery or number of procedures.
Results: the mean school grades were 0.41% lower in the SC than in the CC (95% confidence interval [95 CI], -0.70 to -0.12). There was heterogeneity between the different types of surgery: -1.22% (95 CI, -1.87 to -0.57) for ENT surgery, or 0.93% (95 CI, 0.12 to 1.75) for urological surgery. There was no association between having grades below the 10th percentile and exposure (odds ratio [OR], 1.02; 95 CI, 0.98 to 1.07). In the secondary cohort, the mean school grades were -1.41% lower (95 CI, -2.31 to -0.50) in children with two procedures and -1.82% lower (95 CI, -3.49 to -0.15) in children with three, while in the tertiary cohort they were -0.87% lower (95 CI, -1.11 to -0.64). The mean IT score for the SC was 0.97% lower than for the CC (95 CI, -1.78 to -0.15).
The authors analysed other variables associated with academic achievement. Mean school grades showed a correlation with being male as opposed to female of -9.88 (95 CI, -10.1 to -9.69), with low versus high maternal educational level of -9.89 (95 CI, -10.2 to -9.61) and with being born in December versus January of -5.34 (95 CI, -5.80 to -4.89).
Conclusions: exposure to anaesthesia at age less than 4 years has a small effect on academic and cognitive performance in adolescence. There may be vulnerable groups that are at higher risk.
Conflicts of interest: the authors had no conflicts of interest.
Funding source: various grants from Swedish institutions.