The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

A COMPARISON OF AVERAGE TUBE COMPENSATION AIRWAY AND CARINAL PRESSURES IN A SIMULATED SPONTANEOUSLY BREATHING MODEL FOR THREE MECHANICAL VENTILATORS

D. A. Grooms, BS, RRT1, S. Richey, BS, RRT2


Background: Several new generation ventilators incorporate a Tube Compensation (TC) function which automatically adjusts inspiratory pressure levels in proportion to changes in inspiratory flow rates. The intent is to offset the flow resistive properties of artificial airways in order to maintain a constant carinal pressure throughout inspiration. We hypothesized there would be different airway and carinal pressure between three mechanical ventilators.

Methods: A spontaneously breathing model was utilized using a dual chamber Double TTL test lung (Michigan Instruments). One lung (driver) was ventilated with a Hamilton Galileo ventilator (Hamilton Medical Inc.) using a volume control mode with a sinusoidal flow pattern to generate PIFR’s of 25-40Lpm at the distal end of three ETT’s (7.0, 7.5, 8.0). Respiratory rate of 15bpm and I-time of 0.8 sec were used to generate spontaneous breathing in a second lung (spontaneous). PIFR was measured and validated with the use of a Bicore device while connected to three different ventilators (Hamilton Galileo, Drager Evita XL, and Puritan Bennett 840). Once PIFR was validated, the transducer was removed. Stage I consisted of having all three ventilators set in Spontaneous mode with 0 PS, 0 PEEP, and no TC. Stage II consisted of having the Automatic TC (ATC-Evita XL, 840) and Tube Resistance Compensation (TRC- Galileo) functions active with same settings as Stage I. Pressure data points were measured using the auxiliary pressure (Paux) port on a Hamilton Galileo at the distal (airway) and proximal (carinal) ends of each ETT. The data was captured using Data Logger software (Version 3.3, Hamilton Med.). A total of 17 data points were plotted throughout an 0.8sec inspiratory phase. One way analysis of variance (ANOVA) was used for statistical testing.

Results: Average inspiratory airway and carinal pressures with active ATC/TRC were highest with the PB 840 and lowest with the Hamilton Galileo for all ETT sizes and flow rates (p<0.05) (Table 1). Carinal pressure was not maintained at a constant pressure level throughout inspiration for any ventilator or ETT.

Conclusion: Our results demonstrate that there are statistically significant differences in the amount of pressure each ventilator outputs and maintains at the airway and carinal levels with TC when the same flow rate and pattern is generated through an airway with 0 PEEP and 0 PS set.

Table 1
7.0 ETT 25LPM 35LPM
Stage # 1 2 1 2 1 2 1 2
 Airway Airway Carinal Carinal Airway Airway Carinal Carinal
Evita XL 0 4.62 -1.52 -0.43 -0.1 7.9 -2.04 -0.43
Galileo 0.8 0.1 -1.61 -1.58 -0.32 -0.39 -2.61 -2.77
PB 840 -1.01 4.68 -1.01 0.01 0.7 8.96 -1.89 -0.32
P value 0.003 <0.001 0.310 0.004 0.520 <0.001 0.002 0.005
7.5 ETT 25LPM 40LPM
Evita XL -0.08 4.44 -0.56 0.46 -0.18 8.68 -2.02 0.52
Galileo 0.05 0.08 -0.61 -0.72 -0.13 -0.44 -1.91 -1.86
PB 840 0.71 3.99 -0.52 0.91 0.72 11.39 -1.64 1.09
P value 0.049 <0.001 0.98 0.047 0.137 <0.001 0.781 0.009
8.0 ETT 25LPM 40LPM
Evita XL -0.25 0.78 -0.94 -0.21 -0.45 3.51 -1.48 -0.39
Galileo 0.39 0.12 -0.13 -0.44 -0.33 -0.36 -1.61 -1.3
PB 840 0.76 4.08 -0.2 1.54 0.74 10.88 -0.98 3.44
P value 0.032 <0.001 0.160 0.018 0.031 <0.001 0.480 0.004
Stage 1- 0 PS, 0 PEEP, no ATC/TRC     
Stage 2- 0 PS, 0 PEEP, 100% ATC/TRC     

Numbers represent Average pressure throughout 0.8 sec inspiratory phase.


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