Author(s): Karakurt Z, Fanfulla F, Ceriana P, Carlucci A, Grassi M,
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Abstract PURPOSE: The aim of the study was to evaluate the physiologic determinants of ventilator dependency in patients who underwent major surgery. MATERIALS AND METHODS: In this observational study, 43 stable tracheostomized patients undergoing prolonged ventilation (>14 days) were evaluated. Diaphragmatic muscle function was assessed invasively by the tension-time index of the diaphragm (TTdi), an indicator of diaphragm endurance time. The TTdi was calculated as transdiaphragmatic pressure/maximum transdiaphragmatic pressure × inspiratory time/total respiratory time and was recorded either when weaning from mechanical ventilation had finally been successful (n = 28 patients) or at the end of the fifth week in those patients in whom weaning failed (FW) (n = 15). Furthermore, the characteristics of survivors (n = 33) were compared with those of nonsurvivors (n = 10). RESULTS: Successfully weaned patients had a lower breathing frequency/tidal volume or rapid shallow breathing index compared with FW patients (93.9 ± 45.5 vs 142.4 ± 60.3, respectively; P < .005). The TTdi was significantly higher in FW than in successfully weaned patients (0.107 ± 0.050 vs 0.148 ± 0.059; P < .023) and in nonsurvivors than in survivors (0.106 ± 0.046 vs 0.174 ± 0.058, P < .0001, respectively). A transdiaphragmatic pressure/maximum transdiaphragmatic pressure ratio of more than 40\% was an independent predictor of mortality, whereas an increased frequency/tidal volume ratio and TTdi were independent predictors of weaning failure. CONCLUSIONS: Difficult-to-wean patients after major surgery have overall a limited diaphragm endurance time, in particular, FW breathe very close to the fatigue threshold, and they adopt a rapid shallow breathing respiratory pattern to avoid crossing this threshold. Copyright © 2012 Elsevier Inc. All rights reserved.
This article was published in J Crit Care
and referenced in Journal of Nursing & Care