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 5 80) and TTdi greater than 0.15 (n 5 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.Keywords: diaphragm; respiratory muscles; pediatric critical care; weaningPatients are extubated when assessed to be capable of sustaining spontaneous ventilation without respiratory support. Premature extubation leading to cardiorespiratory compromise necessitates reintubation and reinstitution of mechanical ventilation and increases mortality and morbidity (1), whereas prolonged ventilatory support exposes the child to increased risk of nosocomial infection and lung injury (2). Extubation failure has been reported to occur in 4 to 10% of children (3, 4), hence an accurate predictor of extubation outcome would be of significant clinical value (1).Univariate indices that examine a single aspect of physiological function often have poor predictive power probably because they do not fully reflect all the pathophysiological processes affecting extubation outcome (5). Accurate prediction is more likely using multivariate indices that integrate a number of physiological functions (6). Studies of multivariate indices in children, such as the rapid-shallow breathing index (RSB) (respiratory rate [RR] divided by tidal volume [VT]) (5) and the CROP index (compliance, RR, oxygenation, and inspiratory pressure [PI]), however, have been limited and yielded contradictory results. We (7) and others (8, 9) have shown that the predictive power of those indices in children is poor, whereas Baumeister and colleagues (10), demonstrated that the CROP index discriminated strongly between successful an...

Maximal inspiratory pressure (PIMAX), the maximum negative pressure generated during temporary occlusion of the airway, is commonly used to measure inspiratory muscle strength in mechanically ventilated infants and children. There are, however, no guidelines as to how the PIMAX measurement should be made. We compared the maximum inspiratory pressure generated during airway occlusion (PIMAX OCC ) to that when a unidirectional valve (PIMAX UNI ), which allowed expiration, but not inspiration was used.Twenty two mechanically ventilated children (mean (SD) age 4.8 (4.5) years) were studied. Three sets of end expiratory occlusions were performed for each method in random order. The expired volume during PIMAX UNI was assessed and related to the functional residual capacity (FRC) measured using a helium dilution technique.The mean (SD) PIMAX UNI (45.5 (15.2) cmH 2 O) was significantly greater than mean (SD) PIMAX OCC (30.9 (9.0) cmH 2 O) (p<0.0001). The mean (SD) expired volume during PIMAX UNI , was 98 ml (62.3), a mean reduction in FRC of 33.1% (SD 13.9). There were no significant differences between techniques in the baseline respiratory drive, the number of efforts required and the time to reach PIMAX. Regardless of technique, PIMAX was reached in 10 inspiratory efforts or 15sec of airway occlusion.A unidirectional valve allowing expiration, but not inspiration yields greater PIMAX values in children. Occlusions should be maintained for 12 seconds or eight breaths (99% CI of mean).

Ventilator assessment of compliance, but not resistance, using the Evita 4 is reproducible and reliable.