We read with interest Dr. Anand’s Editorial View, “Anesthetic Neurotoxicity in Newborns: Should We Change Clinical Practice?” but we are concerned that readers may misinterpret his indication regarding postnatal day 35 (P35) rhesus monkeys: “anesthetic neurotoxicity primarily results from apoptosis in rodents, … whereas infant monkeys at P5 (but not at P35) exhibit both excitotoxicity and apoptosis.”1Although the report referenced by Dr. Anand in regard to P35 monkeys did not find a neurotoxic effect, it used one control and one experimental sample of n = 3.2For each indicator of neurotoxicity, the SDs bracketing the observed results were far greater than the observed difference between the control group and the anesthetized group, such that a confidence interval around each observed difference includes levels of neurotoxicity that cannot be dismissed. Accordingly, the neurotoxicity of anesthetics has not been established beyond age P5 in a primate model. Absence of evidence is (still) not evidence of absence.3 

*State University of New York, Downstate Medical Center, Brooklyn, New York. john.hartung@downstate.edu

Anand KJ: Anesthetic neurotoxicity in newborns: Should we change clinical practice? Anesthesiology 2007; 107:2–4
Slikker W, Zou X, Hotchkiss CE, Divine RL, Sadovova N, Twaddle NC, Doerge DR, Scallet AC, Patterson TA, Hanig JP, Paule MG, Wang C: Ketamine-induced neuronal cell death in the perinatal rhesus monkey. Toxicol Sci 2007; 98:145–58
Hartung J, Cottrell JE, Giffin JP: Absence of evidence is not evidence of absence. Anesthesiology 1983; 58:298–300