The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

EFFECT OF INTERACTIONS BETWEEN TRACHEAL GAS INSUFFLATION (TGI), MECHANICAL VENTILATION AND TOTAL-PEEP ON PaCO_{2} IN ARDS

Edgar Delgado, RRT, Adelaida Miro, MD, Leslie Hoffman, RN, PhD, Fred Tasota, RN, Michael R. Pinsky, MD. Departments of Respiratory Care, Anesthesiology & CCM, and School of Nursing, University of Pittsburgh Medical Center, Pittsburgh, PA. 15213

TGI flushes CO_{2} from the anatomical airways and decreases dead space ventilation. However, TGI in conjunction with mechanical ventilation (MV) results in the development of auto-PEEP leading to an increase in total-PEEP (PEEP_{vent} + auto-PEEP). As total-PEEP increases, CO_{2} elimination is reduced as a result of the increase in alveolar deadspace. The final effect on PaCO_{2} depends on the interactions between TGI, MV, and total-PEEP. Thus, we sought to measure the effects of TGI on total-PEEP and CO_{2} elimination during volume and pressure control ventilation in patients with ARDS. Methods: TGI catheter was placed 2 cm beyond the distal tip of the endotracheal tube with flow rates of 0 and 10 L/min. Peak airway pressure (Peak Paw) was measured at the proximal end of the endotracheal tube. Minute volume (V_{E}) was derived using respiratory inductive plethysmography (RIP). Group 1A (n=4) volume control ventilation with PEEP_{vent} constant. Group 1B (n=4) pressure control ventilation (PCV) with PEEP_{vent} constant. Group 2 (n=5) PCV with PEEP_{vent} decreased to maintain total-PEEP constant. Data were collected at the end of each 30 minute experimental condition.

Group 1A Group 1B Group 2

TGI(L/min) 0 10 0 0 10 0 0 10 0

Peak Paw 40.1 46.1 41.2 42.3 43.0 42.1 39.1 38.5 40.9

(cm H_{2}O)

V_{E}(L) 9.1 9.3 9.4 10.1 8.6 10.0 11.4 11.3 11.9

Total PEEP 14.9 20.9 14.9 12.5 16.8 12.5 11.3 11.3 11.4

(cm H_{2}O)

PaCO_{2} 46.3 44.8 47.8 60.3 58.3 60.8 65.4 57.6* 67.2

(mm Hg)

*P < 0.05 when compared to zero flow

CONCLUSION: 1. TGI-induced increase in auto-PEEP inhibits the ability to decrease PaCO_{2} due to its effect on total-PEEP and V_{E}. 2. Decreasing PEEP_{vent} during TGI will keep total-PEEP constant, resulting in a lower PaCO_{2} for a constant V_{E}.

OF-97-148

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