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Tension–Time Index as a Predictor of Extubation Outcome in Ventilated Children

¹ Department of Child Health, and ⁵ Respiratory Medicine, King's College London, Division of Asthma, Allergy and Lung Biology, King's College London School of Medicine at Guy's, King's College and St Thomas' Hospitals; ² Paediatric Intensive Care Unit, and ⁴ Aneasthetic Department and Intensive Care Unit, King's College Hospital NHS Trust; and ³ Paediatric Intensive Care Unit, St Mary's Hospital NHS Trust, London, United Kingdom

Correspondence and requests for reprints should be addressed to Gerrard F. Rafferty, Ph.D., Department of Child Health, 4th Floor Golden Jubilee Wing, King's College London School of Medicine, Bessemer Road, London SE5 9PJ, UK. E-mail gerrard.rafferty{at}kcl.ac.uk

Rationale: Indices that assess the load on the respiratory muscles, such as the tension–time index (TTI), may predict extubation outcome.

Objectives: To evaluate the performance of a noninvasive assessment of TTI, the respiratory muscle tension time index (TTmus), by comparison to that of the diaphragm tension time index (TTdi) and other predictors of extubation outcome in ventilated children.

Methods: Eighty children (median [range] age 2.1 yr [0.15–16]) admitted to pediatric intensive care units at King's College and St Mary's Hospitals who required mechanical ventilation for more than 24 hours were studied.

Measurements and Main Results: TTmus, maximal inspiratory pressure, respiratory drive, respiratory system mechanics, and functional residual capacity using a helium dilution technique, the rapid shallow breathing and CROP indices (compliance, rate, oxygenation, and pressure) indexed for body weight were measured and standard clinical data recorded in all patients. TTdi was measured in 28 of the 80 children using balloon catheters. Eight children (three in the TTdi group) failed extubation. TTmus (0.199 vs. 0.09) and TTdi (0.157 vs. 0.07) were significantly higher in children who failed extubation. TTmus greater than 0.18 (n = 80) and TTdi greater than 0.15 (n = 28) had sensitivities and specificities of 100% in predicting extubation failure. The other predictors performed less well.

Conclusions: Invasive and noninvasive measurements of TTI may provide accurate prediction of extubation outcome in mechanically ventilated children.

Key Words: diaphragm • respiratory muscles • pediatric critical care • weaning

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Extubation failure is a recognized problem in pediatric intensive care and clinicians are frustrated by their inability to accurately predict extubation outcome. What This Study Adds to the Field Our results suggest that invasive and noninvasive measurements of tension–time index, which are assessments of the load/capacity balance of respiratory muscles, may accurately predict extubation outcomes in mechanically ventilated children.