The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

A COMPARISON OF TOTAL PATIENT WORK OF BREATHING (TPWOB) ASSOCIATED WITH DIFFERENT SIZES OF ENDOTRACHEAL AND TRACHEOSTOMY TUBES IN A LUNG MODEL.

Jennifer L. Boenisch, BS, CRT; David L. Vines, MHS, RRT; Brandi Blackburn, BS, CRT; David C. Shelledy, PhD, RRT; Jay Peters, MD. The University of Texas Health Science Center at San Antonio.

BACKGROUND: It is thought that tracheostomy tubes (TT) provide a significantly lower TPWOB and resistance compared to endotracheal tubes (ETT). To test this assumption, we compared TPWOB, peak inspiratory flow (PIF), inspired and expired tidal volume (VT), peak inspiratory pressure (PIP), mean airway pressures (MAP), and airway resistance (Raw) between 8.0 mm ID ETT, 8.0 mm ID TT, 7.0 mm ID ETT, 7.0 mm ID TT, 6.0 mm ID ETT, 6.0 mm ID TT, 5.0 mm ID ETT, and 5.0 mm ID TT.

METHODS: Spontaneous breathing was simulated using a two-compartment mechanical lung model (Michigan Instruments Inc., Grand Rapids, MI). The driver lung B was attached to a Bennett 7200 (Puritan Bennett, Pleasanton, CA). Work of breathing (WOB) was first measured on lung B alone at VT of 300, 400, 500, and 600 mL while peak flow was varied from 40, 60, 80, and 100 L/min with a sine wave flow pattern using the Ventrak 1550 Respiratory Mechanics Monitoring System (Novametrix Medical Systems, Inc., Wallingford CT). Then WOB was measured at these volumes for lung B to drive lung A at normal compliance (0.05 L/cm H2O) and resistance (2.7 cm H2O/L/sec) while the following airways were attached: 8.0 mm ID ETT (Mallinckrodt Critical Care, GlensFalls, NY), 8.0 mm ID Portex TT (Sims Portex, Inc., Keene, NH) without inner cannula, 7.0 mm ID ETT (Mallinckrodt Critical Care, GlensFalls, NY), 7.0 mm ID Portex TT (Sims Portex, Inc., Keene, NH) without inner cannula, 6.0 mm ID ETT (Mallinckrodt Critical Care, GlensFalls, NY), 6.0 mm ID Portex TT (Sims Portex, Inc., Keene, NH) without inner cannula, 5.0 mm ID ETT (Mallinckrodt Critical Care, GlensFalls, NY), and a 5.0 mm ID #4.0 Shiley TT (Mallinckrodt, St. Louis, MO). We also measured the WOB for lung B to drive lung A attached to the various airways while receiving assistance from pressure support ventilation (PSV). PSV levels of 5, 10, 15 and 20 cm H2O were used. TPWOB was calculated using the following formula: [TPWOB= WOB(B+A) - WOBB]. PIF, inspired and expired VT, PIP, and MAP were measured using a CO2SMO Plus (Novametrix Medical Systems, Inc., Wallington, CT). Resistance for the various airways was calculated by subtracting plateau pressure from PIP while inspiratory flow was set at 1 L/sec and VT set at 800 mL.

RESULTS: The calculated airway resistance for the various airways was as follows: 6 cm H2O/L/sec for the 8.0 mm ID ETT, 3 cm H2O/L/sec for the 8.0 mm ID TT, 9 cm H2O/L/sec for the 7.0 ETT, 4 cm H2O/L/sec for the 7.0 TT, 15 cm H2O/L/sec for the 6.0 ETT, 7 cm H2O/L/sec for the 6.0 TT, 29 cm H2O/L/sec for the 5.0 ETT, and 18 cm H2O/L/sec for the 5.0 TT. The TPWOB was significantly less (p<0.05) for the 8.0 mm ID ETT (0.705 + 0.407J/L), 8.0 mm ID TT (0.595 + 0.370 J/L), 7.0 mm ID ETT (0.842 + 0.437 J/L), 7.0 mm ID TT (0.658 + 0.399 J/L), 6.0 mm ID TT (0.764 + 0.411 J/L) compared to the 6.0 mm ID ETT (1.035 + 0.474 J/L), 5.0 mm ID ETT (1.318 + 0.470 J/L), and the 5.0 mm ID TT(1.088 + 0.471 J/L). The TPWOB was also significantly less (p<0.05) for the 8.0 mm ID TT (0.595 + 0.370 J/L) and the 7.0 mm ID TT (0.658 + 0.399 J/L) compared to the 7.0 mm ID ETT (0.842 + 0.437 J/L). The TPWOB was significantly less (p<0.05) for the 6.0 mm ID ETT (1.035 + 0.474 J/L) and 5.0 mm ID TT (1.088 + 0.471 J/L) compared to 5.0 mm ID ETT (1.318 + 0.470 J/L). There were no significant differences (p<0.05) in inspired and expired VT, PIP, or MAP between the various airways across all conditions.

CONCLUSION: The TPWOB for an 8.0 mm ID ETT was not significantly different (p< 0.05) than the 8.0 mm ID TT. For the 7.0, 6.0, and 5.0 mm ID airways the TPWOB for the TTs were significantly less (p< 0.05) compare to the ETTs. Performing tracheotomies in patients with a 7.0 mm ID or smaller ETT may result in less resistive WOB.

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