Ultrasound-Guided Obturator Nerve Block

We agree with Drs. Sanatani and Whyte1 that the value of the Tp-e interval as a surrogate marker of transmural dispersion of repolarization remains to be proven. Indeed, their previous studies of anesthetic effects include normal values for children, which will contribute to establishing a normal reference range. We have not suggested that the upper limit of the Tp-e interval of 65 milliseconds is normal in children. Rather, we have referenced pooled data from adult studies on the normal range for transmural dispersion of repolarization.2–4 In his review of pooled adult studies, Surawicz concluded that the “normal ” value of QT dispersion was at an average of <65 milliseconds in patients with and without heart disease, and in those patients who had ventricular tachyarrhythmias but structurally normal hearts. Also of interest, in studies in patient groups with QT dispersion in the range of 66 to 115 milliseconds (e.g., survivors of short- and long-term myocardial infarction, hypertrophic cardiomyopathy with ventricular arrhythmias or tetralogy of Fallot with right ventriculotomy and ventricular arrhythmias, and patients with long QT syndrome who responded to β-blocker therapy), many were at increased risk of serious ventricular arrhythmia or sudden cardiac death. Therefore, we did not further elaborate on Tp-e intervals in children and do not advocate any specific Tp-e interval as safe at this time. Finally, we agree that both a valid normal reference range and abnormal values predictive of adverse events need to be developed. Aruna T. Nathan, MBBS, FRCA David R. Jobes, MD Department of Anesthesiology and Critical Care Medicine Division of Cardiothoracic Anesthesia The Children's Hospital of Philadelphia The University of Pennsylvania Philadelphia, Pennsylvania [email protected](Nathan, Jobes)