To the Editor:—
We commend Dr. Wilder et al.1
for their work titled “Early Exposure to Anesthesia and Learning Disabilities in a Population-based Birth Cohort.” In their article, they report that patients younger than 4 yr, with two or more exposures to general anesthesia, had a greater proportion of learning disabilities (LDs) compared with children who had one or no exposure to general anesthesia. This represents a clinically important epidemiologic correlate to compliment the worrying animal observations demonstrating the detrimental effects of general anesthesia on the developing brain.
A primary assumption in cohort analyses is that the groups observed are the same before exposure. However, children requiring anesthesia for surgical treatment may be inherently different from those who do not; these differences may present unique factors that predispose to LDs independent of anesthesia per se
. In particular, we are concerned that a subpopulation at risk for learning disabilities—children undergoing ears, nose, and throat surgery—is overrepresented. Typical ears, nose, and throat surgeries in this age group include adenotonsillectomy and bilateral myringotomy with tympanostomy tube placement. The former is associated with obstructive sleep apnea, which can result in neurocognitive defects2
; the latter may be associated with otitis media with effusions, which can yield poor performance in expressive speech and math testing in younger children.3
These coexisting conditions may have skewed the diagnosis of LD in this population. This is relevant because children tested within a short period of time from their ears, nose, and throat surgery may not have had sufficient time to “catch up” with their peers in terms of testing, should the surgery have improved their condition. Furthermore, given the frequency of achievement tests administered to the cohort population, is it possible to find children who no longer met LD definitions at some time point during follow-up testing? This would be of particular interest for those children undergoing ears, nose, and throat surgeries.
In addition, we are concerned that the third definition of LD included patients in the low-average IQ range versus average intelligence. Moreover, using a cutoff of 1.75 SDs below their predicted standard score, as opposed to the conventional 2 SDs, might be an oversensitive method of identifying patients with LDs.
We are interested to know whether the authors could remove patients who underwent adenotonsillectomy and bilateral myringotomy with tympanostomy tube surgeries from the analysis and apply conventional definitions of LD to determine whether a relation between general anesthesia and LD persists.
Christopher L. Pysyk, M.D.,
Kimmo Murto, M.D., F.R.C.P.C.
Sally Kuehn, Ph.D.
Dermot R. Doherty, M.B., B.Ch., F.C.A.R.C.S.I.*
*Children's Hospital of Eastern Ontario, University of Ottawa, Ottawa, Ontario, Canada. firstname.lastname@example.org
1. Wilder RT, Sprung J, Katusic SK, Barbaresi WJ, Mickelson C, Gleich SJ, Schroeder DR, Weaver AL, Warner DO: Early exposure to anesthesia and learning disabilities in a population-based birth cohort. Anesthesiology 2009; 110:796–804
2. Giordani B, Hodges EK, Guire KE, Ruzicka DL, Dillon JE, Weatherly RA, Garetz SL, Chervin RD: Neuropsychological and behavioral functioning in children with and without obstructive sleep apnea referred for tonsillectomy. J Int Neuropsychol Soc 2008; 14:571–81
3. Roberts JE, Burchinal MR, Zeisel SA: Otitis media in early childhood in relation to children's school-age language and academic skills. Pediatrics 2002; 110:696–706
© 2009 American Society of Anesthesiologists, Inc.