The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

CONTINUOUS VS. EXPIRATORY TRACHEAL GAS INSUFFLATION PRODUCE THE SAME LEVELS OF AUTO-PEEP.

Edgar Delgado, BS. RRT; Adelaida M Miro, MD; Frederick J Tasota, MS, RN; Leslie A Hoffman, PhD, RN; Thomas McCormick, AS; Michael R Pinsky, MD. Departments of Respiratory Care and Anesthesiology/CCM University of Pittsburgh Medical Center and University of Pittsburgh School of Nursing. Pittsburgh, PA.

Tracheal gas insufflation (TGI) is used in conjunction with mechanical ventilation to enhance CO_{2} elimination, but it has been described to cause the development of auto-PEEP. TGI may be delivered continuously during the entire respiratory cycle (C-TGI) or it may be synchronized to flow only during the expiratory phase (E-TGI). Although both delivery techniques augment CO_{2} elimination, it has been proposed that E-TGI is associated with less auto-PEEP than C-TGI. One potential explanation for this observation is that C-TGI will increase total minute ventilation (V{E}) if the ventilator circuitry is not properly adapted to vent excess TGI. In order to avoid this problem, we have previously described (Resp Care 1995, 40:11;1196) insertion of a pressure relief valve in the ventilator circuitry to keep V_{E} constant during C-TGI. Because both C-TGI and E-TGI produce the same "back pressure" and thus, similarly increase expiratory resistance, we hypothesized that as long as V_{E} was kept constant, auto-PEEP levels would be identical under conditions.

Methods: A catheter was inserted into the airway of a calibrated adult training test lung model (TTL #2600i) for TGI. Peak intrapulmonary inspiratory pressure (P_{peak}) and end-expiratory intrapulmonary pressure (Auto-PEEP) were measured with a calibrated pressure transducer. Total V_{E} represents the sum of the ventilator-derived volume and TGI contribution. Pressure-control ventilation (Puritan Bennett 7200) with set pressure = 35 cm H_{2}O, frequency = 20 bpm, and PEEP = 0 was used. Fixed artificial lung parameters were compliance = 0.02 L/cm H_{2}O and resistance = 20 cm H_{2}O/L/sec. I:E ratio was varied at 1:1 and 2:1. During the experimental protocol, a control and 3 separate TGI conditions at 10 L/min were evaluated: (1) Control (no TGI), (2) Continuous TGI (no valve), (3) Continuous TGI (yes valve), (4) Expiratory TGI.

Control Continuous TGI Continuous TGI Expiratory TGI

(No Valve) (Yes Valve)

I:E Ratio 1:1 2:1 1:1 2:1 1:1 2:1 1:1 2:1

V_{E}(L) 12.3 13.0 14.6 15.3 12.5 12.4 12.5 12.2

Auto-PEEP 0.2 8.4 3.7 14.1 2.8 9.7 2.8 9.5

(cm H_{2}O)

P_{peak} 31.6 32.8 33.9 37.9 30.1 31.5 31.9 32.8

(cm H_{2}O)

CONCLUSION: We conclude that the increase in auto-PEEP levels during C-TGI is secondary to an increase in V_{E} resulting from inadequate venting of the excess gas. When V_E} is kept constant by insertion of a pressure relief valve, C-TGI vs. E-TGI produce the same levels of auto-PEEP.

Reference: OF-96-150

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