title: Different tracheotomy tube diameters influence diaphragmatic effort and indices of weanability in difficult to wean patients.
abstract: 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. (PTP(di/min)), lung compliance and resistance (C(L) and R(L)), breathing pattern, tension-time index of the diaphragm (TT(di)), and the ratio of breathing frequency to tidal volume (f/V(T)) 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 PTP(di) (337.63 ± 194.35 cm H(2)O · s/min vs 263.28 ± 156.23 cm H(2)O · s/min for 6.5 mm and 8 mm, respectively, P = .004) and R(L) (16.74 ± 8.10 cm H(2)O · s/min vs 11.72 ± 7.88 cm H(2)O · s/min, respectively, P = .008). Both weanability indices were also significantly higher using the smaller tube: f/V(T) 93.32 ± 20.91 vs 77.06 ± 19.26 for 6.5 mm and 8 mm, respectively, P < .02; TT(di) 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 PTP(di), f/V(T), and TT(di), 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.
authors.affiliation: Azienda Opedaliera Universitaria Sant Orsola-Malpighi, Bologna, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Valentini
authors.forename: Eva
authors.initials: E
authors.lastname: Tonveronachi
authors.forename: Cesare
authors.initials: C
authors.lastname: Gregoretti
authors.forename: Chiara
authors.initials: C
authors.lastname: Mega
authors.forename: Luca
authors.initials: L
authors.lastname: Fasano
authors.forename: Lara
authors.initials: L
authors.lastname: Pisani
authors.forename: Stefano
authors.initials: S
authors.lastname: Nava
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003964:Diaphragm / Q000502:physiology*; D004734:Energy Metabolism; D004867:Equipment Design; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal; D008297:Male; D014140:Tracheotomy / Q000295:instrumentation*; D015300:Ventilator Weaning; D014939:Work of Breathing