The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

COMPARISON OF RESPONSE TIMES AND WORK OF BREATHING UTILIZING THREE FLOW SENSORS

M. J. Heulitt1, 2, S. J. Holt2, T. L. Thurman2, A. E. Gibbs2

Background: Ventilator manufacturers have recently incorporated flow sensors at the patient wye to provide a more accurate measurement of delivered VT. The type of flow sensor used may have an effect on patient work of breathing (WOBP).

Methods: Intubated, sedated, spontaneously breathing, male porcine (n=14) were ventilated with PSV utilizing two different ventilators, one using a fixed orifice flow sensor (FOF), and the other utilizing a hot wire flow sensor (HWF), and a variable orifice flow sensor (VOF), independently. Ventilator work of breathing (WOBV) and WOBP were obtained using a Bicore® monitor with an esophageal balloon and a separate flow transducer. Breath waveforms were acquired utilizing a heated 0-35 L/min pneumotachograph calibrated for flow, pressure, and volume and analyzed for ventilator response times from a computerized digital recorder. Data were analyzed using ANOVA with p<0.05.

Results: Pigs mean weight 8.4 kg + 6.9. Mean + SD for response time measurements and WOBP and WOBV are listed in the table below. We found that WOBP was less in the FOF (p<0.001) and HWF (p<0.001) when compared to the VOF. The area of the pressure curve was increased in the VOF when compared to the FOF (p<0.001) and the HWF (p<0.001). Delta pressure was lower for the HWF when compared to the FOF (p<0.001) and the VOF (p<0.001).

Conclusions: This study suggests that even though the flow sensors tested do not directly trigger breaths, WOBP and measured response times may be affected by flow sensors. Certain flow sensors, by their design, may create resistance in the patient circuit due to physical impedance.

Mean + SD
 FOF HWF VOF
WOBP [joule/L] 0.38+0.38 0.43+0.41 0.76+0.65
WOBV [joule/L] 0.34+0.12 0.26+0.22 0.25+0.17
    
Delta t (initiation of breath to negative pressure) [ms] 77+28 96+138 88+71
Delta t (initiation of breath to PIP) [ms] 679+156 687+216 677+181
Area pressure curve (initiation of breath to return to baseline pressure)[cm H2O*sec] 0.11+0.08 0.09+0.08 0.19+0.20
Delta t (initiation of breath to PF)[ms] 307+87 281+87 309+79
Delta p (initiation of breath to PIP)[cm H2O] 1.25+0.82 0.83+0.71 1.22+0.84
MAP [cm H2O] 2.91+0.44 2.99+0.48 3.08+0.38



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