The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

VENTILATORY PATTERN RESPONSES TO VARYING COMPLIANCE AND RESISTANCE IN A LUNG MODEL WITH ADAPTIVE SUPPORT VENTILATION

M. A. Gentile1, J. M. Davies1, N. R. MacIntyre1


Background: Adaptive Support Ventilation (ASV) is a pressure limited, time-cycled, closed-loop mode of mechanical ventilation. For a given set minute ventilation, ASV provides a frequency-tidal volume (VT) pattern based on a “minimal work, minimal air trapping” principle. The purpose of this study was to assess the ventilatory pattern and plateau pressures generated by ASV under different conditions of compliance (CL) and resistance (Raw).

Method: A Hamilton Galileo with ASV (Hamilton Medical, Reno, NV) was set at 100% support for an ideal body weight of 70kg and connected to a dual chambered test lung (TTL, Michigan Instruments, Inc., Grand Rapids, MI). Applied PEEP was 5 cm H2O. Tidal volume, rate and plateau pressure were recorded at set CL values of 100, 60, 40, and 20 mL/cm H2O coupled with the use of endotracheal tube (ETT) sizes 8.0, 5.0 and 4.0 mm to simulate different Raw conditions.

Conclusion: Under “stiff lung” conditions, especially in the presence of high airway resistance, ASV tends to give higher VTs than those recommended by the NIH ARDS Network. However, except at the extremes of low compliance, ASV maintained Pplat below 30 cm H2O. Under “obstructed lung” conditions, especially in the presence of high compliance, ASV tends to deliver very high VTs. However, only under the highest resistance-highest compliance conditions did ASV settings result in PEEPi. For clinicians to reduce VTs beyond those chosen by ASV, total minute ventilation reduction is the only option.

Results
ETT Size 8 8 8 8 5 5 5 5 4 4 4 4
Set CL 100 60 40 20 100 60 40 20 100 60 40 20
Calc. Raw 4 3 4 16 18 19 20 20 38 37 44 41
VT (mL) 650 555 498 415 801 666 592 512 919 767 680 578
VT
(mL/kg)
9 8 7 6 11 9 9 7 13 11 10 8
Rate 11 13 14 17 8 10 11 14 8 9 10 12
Pplat 12 15 18 28 13 16 20 31 16 18 22 33
PEEPi 0 0 0 0 0 0 0 0 2 1 0 0



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