The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

USE OF A RELIEF VALVE (RV) TO ELIMINATE THE RISE IN PEAK AIRWAY PRESSURE SEEN DURING TRACHEAL GAS INSUFFLATION WITH PRESSURE-CONTROL VENTILATION.

Edgar Delgado, BS, RRT. Diane Gowski, MD, Adelaida Miro, MD, Leslie Hoffman, PhD, RN, Fred Tasota, MS, RN, Michael R. Pinsky, MD. Departments of Respiratory Care, Critical Care Medicine, and Nursing, University of Pittsburgh Medical Center, Pittsburgh, PA.

The primary goals of pressure-control ventilation (PCV) and tracheal gas insufflation (TGI) are to minimize peak airway pressure (P_{peak}) and total tidal volume (Vt_{tot}) in an attempt to reduce ventilator-induced lung injury. Both techniques have been utilized independently and in combination. In the clinical application of TGI with PCV, we observed an increase in P_{peak} above the set inspiratory pressure (P_{set}). This rise in P_{peak} may lead to alveolar overdistention and negate the beneficial effects of TGL. We reasoned that the increase in P_{peak} was due to the inability of the circuit to relieve the excess volume from TGI. We hypothesized that use of an in-line RV would eliminate this increase in P_{peak}.



Methods: A catheter was inserted into the airway of a calibrated adult training test lung (TTL #2600i) for gas insufflation. Auto-PEEP was measured as the end-expiratory intrapulmonary pressure with an independent, calibrated pressure transducer. Vt_{tot} represents the sum of the ventilator-derived tidal volume (pneumotachography) and TGI contribution. A Puritan Bennett 7200 ventilator with a conventional non-disposable non-heated wire circuit was utilized with a spring loaded pressure RV (Bird, Inc. #04230) mechanically adjusted to achieve a threshold pressure = P_{set} in the ventilatory circuit's inspiratory limb. Fixed ventilatory parameters were frequency=10 bpm, P_{set}=35 cmH_2O, resistance=5 cmH_2O/L/sec, compliance=.02 L/cmH_2O and I:E ratio=1:1. Catheter flow rate (Vdot_{cath}) was varied as follows:

Vdot_{cath}P_{peak}(cmH_2O)Vt_{tot}(ml)auto-PEEP(cmH_2O)

(L/min)RV onRV off RV on RV offRV on RV off

0 3535 687 689 00

2 3537 691 722 00

6 3543 699 874 11

103551 703 103022



Conclusions: Increasing catheter flow rate resulted in progressive rise in both P_{peak} and Vt_{tot} with the conventional PCV circuit. Insertion of a RV maintained P_{peak} and Vt_{tot} constant. A slight increase in auto-PEEP was noted as Vdot_{cath} increased.

OF-95-042

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