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OBJECTIVE: To determine the effects of different tracheotomy tube sizes on diaphragm effort and weanability indices. METHODS: Ten tracheotomized and difficult to wean subjects were randomized to 2 T-piece trials, with different tracheotomy tube diameters: inner diameters 8 mm and 6.5
mm. Diaphragm pressure-time product per min. (PTPdi/min), lung compliance and resistance (CL and RL), breathing pattern, tension-time index of the diaphragm (TTdi), and the ratio of breathing frequency to tidal volume (f/VT) were recorded.
In an in vitro model, the flow-pressure relationship was measured using the 2 tracheotomy tubes and 2 endotracheal tubes of the same diameter. RESULTS: The use of a smaller diameter resulted in an increase of PTPdi (337.63 ± 194.35 cm H2O · s/min vs 263.28
± 156.23 cm H2O · s/min for 6.5 mm and 8 mm, respectively, P = .004) and RL (16.74 ± 8.10 cm H2O · s/min vs 11.72 ± 7.88 cm H2O · s/min, respectively, P = .008). Both weanability indices were
also significantly higher using the smaller tube: f/VT 93.32 ± 20.91 vs 77.06 ± 19.26 for 6.5 mm and 8 mm, respectively, P < .02; TTdi 0.09 ± 0.052 vs 0.08 ± 0.04, respectively, P < .02. In vitro measurements confirmed that
the resistances were higher with the smaller diameter and similar between the tracheotomy tubes and the endotracheal tubes of the same diameters. CONCLUSIONS: In tracheotomized difficult to wean subjects the decrease of the tracheotomy tube size was associated with an increased PTPdi,
f/VT, and TTdi, that were otherwise normal, using a higher diameter. The in vitro study showed that the resistances increased similarly for tracheotomy tube and endotracheal tube, decreasing the diameter and increasing the flows.