The role of the capnography head-up tilt test in the diagnosis of syncope in children and adolescents.

OBJECTIVES To evaluate the role of the capnography head-up tilt test (CHUTT) in the diagnosis of syncope in pediatric patients. METHODS The CHUTT is a head-up tilt test with concomitant capnometry. Hyperventilation on CHUTT was diagnosed when the patient's end-tidal carbon dioxide pressure (ETPCO2) was </=25 mm Hg. Hyperventilation syncope was diagnosed when three criteria were met: loss of consciousness, ETPCO2 </=25 mm Hg, and no significant drop in blood pressure. The cohort included 65 consecutive children and adolescents (mean age, 14.2 years) who were assessed for syncope by routine investigations and CHUTT. RESULTS The cause of the syncope was established in 67% of cases: cardioinhibitory reaction in 17%, vasodepressor in 20%, psychogenic in 22%, and mixed neurally mediated-psychogenic in 8% of the patients. The history indicated a cause of syncope in 40%, the CHUTT in 49%, and a combination of the history and positive CHUTT in 66% of patients. Neither the patients' clinical data nor values of the blood pressure, heart rate, respiratory rate, and ETPCO2 measured during recumbency predicted which patients would manifest hyperventilation or hyperventilation syncope on tilt. CONCLUSIONS The CHUTT contributes substantially to the diagnosis of syncope in pediatric patients. The CHUTT advances the understanding of the pathophysiological mechanisms of syncope and enables the physician to reassure the patient regarding the essentially benign nature of the condition. Because it is not possible to predict which patients would develop a hyperventilation syncope on the standard tilt test, the modification of this procedure by measuring the ETPCO2 for the assessment of children with syncope should be considered.