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Effects of Pressure Support Ventilation or Tube Compensation, and Tracheal Tube Size and Length on Tidal Volume during Spontaneous Breathing - A Simulator Study -
Masato Hosoya, M.D., Taro Mizutani, M.D., Ph.D., Shinji Takahashi, M.D., Ph.D., Hidenori Toyooka, M.D., Ph.D.
Anesthesia, Mito Saiseikai General Hosptal, Mito, Ibaraki, Japan.

In patients undergoing mechanical ventilation, low level pressure support ventilation (PSV) or tube compensation (TC) appears to be effective to compensate circuit and/or tracheal tube resistance during spontaneous breathing. However, it is controversial whether or not this compensation is appropriate. Therefore, we examined the interaction between PSV or TC, and tracheal tube size and length in terms of changes in tidal volume (VT) during spontaneous breathing using a breathing simulator (ASL 5000).


The ASL 5000 (IngMar Medical, Pittsburgh, PA) is a digitally controlled real time breathing simulator, allowing to create various types of breath including spontaneous ventilation. The ASL5000 was connected to a ventilator (PB-840, Puritan Bennett Inc, Pleasanton, CA), via a standard breathing circuit and either short (20-22 cm) or long (original length) tracheal tube of various sizes, i.e., internal diameter (mm) = 6.5, 7.5, 8.5, and 4.0 or 5.0 MLT (Mallinckrodt, Hazelwood, MO) tube. The ASL 5000 settings were as follows: one compartment model; R = 10 cmH2O/L/s; C = 50 mL/cmH2O; Pmuscle = -10 cmH2O (semi-sinusoidal waveform); f = 12. PB-840 settings were as follows: spontaneous breathing mode; PEEP = 5 cmH2O; PSV = 0, 4, and 6 cmH2O, or TC activated according to each tube size. Also, VT without a tracheal tube was measured as the control value. VT was measured by ASL5000. Data were analyzed by ANOVA and Student’s T-test, and considered significant when p<0.05.

Results (Figure)

In larger size tubes (7.5 and 8.5 mm), compared with VT values without a tracheal tube, VT was smaller during TC, whereas they were larger during PSV at 4 or 6 cmH2O. In almost every tube, compared with VT values for PSV at 0 cmH2O (i.e., no compensation), the increases in VT were significant during PSV at 4 or 6 cmH2O, although they were insignificant during TC.


Under these study conditions, it appears that, in terms of changes in VT, TC undercompensates circuit and/or tracheal tube resistance during spontaneous breathing whereas even low level PSV overcompensates it as long as larger tracheal tubes (≥ 7 mm) are used.

Anesthesiology 2003; 99: A428
Figure 1