A Bench Study Evaluation of the Amount of AutoPEEP When Ventilating an Electronic Lung Model Simulated to Represent Normal, ARDS and COPD Conditions

Abstract

Background: The purpose of this study was to evaluate the occurrence of Auto-PEEP in VC A/C when ventilating normal, ARDS and COPD lung models on the Servo-i, Drager V500, PB 980 and Avea. Methods: This study was completed using an IngMar Medical ASL 5000 electronic lung simulator (ASL 5000) setup to simulate normal, ARDS and COPD conditions. Normal lung: Cst 54 mL/cm H₂O, inspiratory resistance (Rin) 13 cm H₂O/L/s, expiratory resistance (Rout) 12 cm H₂O/L/s; ARDS: Cst 39 mL/cm H₂O, Rin 12 cm H₂O/L/s, Rout 14 cm H₂O/L/s; COPD: Cst 59 mL/cm H₂O, Rin 22 cm H₂O/L/s, Rout 18 cm H2OL/s. VC A/C parameters were set using 70 kg PBW and a tidal volume of 6 mL/kg. Respiratory rates of 15, 20 and 25 breaths/min with a tidal volume of 420 mL were chosen to achieve a minute ventilation of 90 mL/min/kg, 120 mL/min/kg, and 150 mL/min/kg. PEEP was set at 5 cm H₂O throughout the study. Peak flow and I-time were adjusted to maintain an I:E ratio of 1:3 for normal and ARDS conditions. An I:E ratio of 1:4 was used for COPD conditions. A decelerating flow waveform was used, when available. The same circuit was used for each ventilator. The y-piece of the ventilator circuit was attached to the ASL 5000 using a 7023 Hans Rudolph 22 mm adapter. With each change in minute ventilation, the conditions were stabilized for one minute before data collection. Data were collected on each ventilator for each minute ventilation and lung condition for two minutes. Results: As respiratory rate increased, an increase mean pressure, Auto-PEEP and total PEEP were observed in each ventilator. Conclusions: A reduction in expiratory time causes an increase in mean pressure, Auto-PEEP, and total PEEP in all conditions with all ventilators. The Servo-i showed the lowest amount of Auto-PEEP with the Avea yielding the highest amount of Auto-PEEP in all patient conditions. Due to the possible physiological consequences of Auto-PEEP in critically ill patients, further research is needed to evaluate the presence of Auto-PEEP in the clinical setting with mechanically ventilated patients.

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