The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

LABORATORY EVALUATION OF THREE 'DUAL-CONTROL' (DC) MODES OF MECHANICAL VENTILATION (MV).

James J Lawson RRT, Robert S Campbell RRT, Reynaldo P Sinamban MD, Jay A Johannigman MD, Kenneth Davis Jr. MD, Scott B Frame MD, Richard D Branson RRT. University of Cincinnati College of Medicine, Cincinnati, OH 45267-0558.

INTRODUCTION: DC modes of MV combine the positive attributes of volume-controlled (VCV) (safety, preset guaranteed minute ventilation) and pressure-controlled (PCV) (improved gas distribution/exchange, lower ventilating pressures, improved patient-ventilator synchrony) MV. We designed a lung model study to determine ventilator output of three ventilators set to provide DC ventilation in the face of varying ventilatory load conditions [altered Compliance (C) and Resistance (R)]. Methods: Three DC ventilator modes were tested: autoflow (Evita4, Drager, Telford, PA), adaptive pressure ventilation (APV) (Galileo, Hamilton Medical, Reno, NV), pressure regulated-volume control (PRVC) (300, Siemens Medical, ,New Jersey) and compared with VCV. Each technique utilizes pressure-limited, time-cycled breath delivery and allows the PIP to vary breath-to-breath in order to maintain the target V_{T}. Each vent was set to provide a V_{T} of 0.7 L, T_{i} of 1.6 sec, PEEP of 5 cmH_{2}O, and rate of 15 bpm to one side of a two-chambered test lung (TTL). TTL C was set to 20, 40, and 60 mL/cmH_{2}O and R was set to 5 or 25 cmH_{2}O/L/sec. Bicore CP-100 was used to measure pressure, volume, and flow in the proximal airway. Parameters measured by each ventilator included PIP, V_{T}, V_{e}, P_{aw}, R_{aw}, C_{RS}, PIFR, and PEFR. Results: DC MV provides decelerating flow with higher PIFR than VCV (54 vs 26 L/min). Table 1 reveals measured data with each DC mode with varying C and set R of 25.

Table 1. C PIP P_{aw} V_{T} lung V_{T} vent PIFR

20 41 18 660 656 60

APV 40 28 14 650 665 46

60 25 13 660 654 42

20 37 16 575 674 62

Autoflow 40 23 12 572 717 49

60 19 10 570 699 43

20 35 17 535 588 62

PRVC 40 24 13 575 614 54

60 21 12 590 614 47

Table 1. V_{E} lung V_{E} vent

9.9 9.8

APV 9.7 9.9

9.8 9.9

8.5 9.8

Autoflow 8.4 10.1

8.5 9.8

8.1 8.9

PRVC 8.7 9.4

9.0 9.4

PIP, V_{T} and V_{E} delivered to the lung were highest with APV. Drager and Siemens overestimate V_{T} and V_{E} delivered to the lung during VCV and DC MV. V_{T} and V_{E} measured by the Hamilton accurately reflects volume delivery to the lung during VCV and DC MV. Conclusions: DC algorithms vary between ventilator manufacturer. Accurate measurement of V_{T} is essential to assess differences between DC and VCV and to determine pt benefit from DC use.

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

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