The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

LABORATORY EVALUATION OF DIFFERENT METHODS TO PROVIDE TRACHEAL PRESSURE TRIGGERING (TP_{Tr}).

Robert S Campbell RRT, James J Lawson RRT, Richard D Branson RRT. University of Cincinnati Medical Center, Cincinnati, OH 45267-0558.

INTRODUCTION: TP_{Tr} has been shown to eliminate imposed work of breathing (WOB_{i}) and reduce patient work of breathing (WOB_{pt}). TP_{Tr} requires use of a special ET tube with a distal pressure port or the use of a separate sensing tube either through or around the ET tube. We compared work characteristics with various TP_{Tr} techniques in a lung model. Methods: A two-chamber test lung (TTL, Michigan Instruments) was modified to mimic spontaneous breathing with a lift bar. A Hamilton Veolar powered the drive lung using 50% decelerating flow and was set to create demand of 0.5 L V_{T} @ peak flow of 30 L/min at the airway of the "pt lung". A 8.0 ID high/low (Mallinckrodt) and standard 6.0 ID ET tube were used to connect a 7200ae ventilator (Mallinckrodt) to the pt lung. 7200 was set at CPAP - 5 cmH_{2}O and PSV - 5 cmH_{2}O. TP_{Tr} was accomplished via the distal pressure port of the high/low ET tube (H/L), 8 fr pediatric feeding tube (FT) threaded through ET (8FT), 5 fr pediatric FT threaded through ET (5FT), and with a side port adaptor placed at the carina (CAR). Measurements were also made with standard pressure triggering (SPT). Pressure sensitivity was set at -2.0 cmH_{2}O for all conditions. Resistance (R) of each ET was measured with and without the 5 and 8 fr feeding tubes in place. Bicore CP 100 was used to measure pressure, volume, flow, and WOB. Data was compared using student's t-test and p < 0.05 was considered significant. Results: Table 1 reveals the mean measured parameters with each triggering method with 8.0 ID ET tube.

Table 1. PIFR PEFR V_{T} WOB_{vent}

(L/min) (L/min) (mL) (J/L)

H/L 52 25 730 1.02

CAR 58 27 760 1.04

5 FT 67 27 650* 1.86*

8 FT 54 22 700 1.2

SPT 46 25 720 0.67*

Table 1. WOB_{pt} PTP

(J/L) (cmH2O/s)

H/L 0.21 40

CAR 0.17 31

5 FT 0.45* 126*

8 FT 0.20 35

SPT 0.35* 68*

*=p < 0.05 versus all other triggering methods.

ET tube R was 6.6 and 21.1 cmH_{2}O/L/sec for 8.0 and 6.0 ID respectively. With addition of 8 fr FT, R increased to 11.7 and 50.7 cmH_{2}O/L/sec for the 8.0 and 6.0 ID ET tubes respectively. R was 8.9 and 31.1 cmH_{2}O/L/sec with a 5 fr FT placed through the 8.0 and 6.0 ID ET tube respectively. CONCLUSION: Use of 5 fr FT to accomplish TP_{Tr} results in increased WOB and patient-ventilator dysynchrony as a result of the sensing delay caused by the small diameter. Use of larger sensing ports is recommended, even with smaller ET tubes. TP_{Tr} allows the ventilator to overcome the added resistance imposed by the sensing line by measuring and targeting pressure distal to the artificial airway. Future work evaluating the effects of TP_{Tr} with smaller ET tube sizes is warranted. TP_{Tr} with H/L, CAR, and 8 fr FT results in equivalent WOB.

The 44th International Respiratory Congress Abstracts-On-DiskĀ®, November 7 - 10, 1998, Atlanta, Georgia.

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