547 - Does an Increase in PEEP Significantly Increase the Resistive Load in Neonates and Infants? A simulation study

Publication Number: 1526.547

Ibrahim AK. Sammour, Indiana University School of Medicine, Carmel, IN, United States; Steven M. Conlon, Riley Hospital for Children at Indiana University Health, Indianapolis, IN, United States; Rebecca Rose, Indiana University/Riley Hospital for Children at IU Health, Indianapolis, IN, United States

Background: Modern ventilators use near constant bias flow within the ventilator circuit to generate positive end-expiratory pressure (PEEP) against a partially closed expiratory manifold. In theory increasing PEEP at a constant flow rate should increase the resistive load on a patient.

Objective: To evaluate measures of expiratory resistance imposed by ventilators on simulated patients as PEEP is increased.

Design/Methods: Two modern ICU ventilator platforms (Hamilton G5 and Servo U) were used to ventilate a high-fidelity lung simulator (ASL5000, Ingmar Medical) utilizing three different lung models; neonatal RDS, Term newborn, and 10 Kg infant via a size appropriate endotracheal tube. Pressure control was set to 20 cm H2O above PEEP. PEEP increased from 5 to 20 cm H2O incrementally. Bias flow within the circuit was measured at the inspiratory limb using a differential pressure flow sensor (Sensirion SFM3200AW). After allowing for equilibration, 50 breaths per data point were obtained. Expiratory T90 (time for pressure to drop by 90% towards PEEP) was extracted. Peak expiratory flow (PEFR), plateau pressure, and PEEP measurements were used to calculate resistance. Time for PEFR to decay by 90% was measured manually in 10 different breaths per data point. Bias flow was measured using Sigview (SignalLab) by averaging the last 500 ms prior to breath delivery. Data was analyzed using Linear regression (Minitab).

Results: There was significant disparity in bias flow between the two ventilators consistent with their specification sheets. There was a measurable increase in imposed resistance by the Servo U ventilator regardless of simulated model used as evidenced by a longer PEFR decay time, a longer expiratory T90, and higher total resistance. The impact of increasing PEEP on imposed resistance measures appears to be small.

Conclusion(s): Ventilator design appears to have a more pronounced impact on imposed resistance to exhalation than PEEP escalation. Further evaluation of devices on the market is needed.

Table: Settings
Top: ASL5000 Model settings
Bottom: Ventilator settings



Results:
Scatterplots of Bias flow, PEFR decay time, Expiratory T90, and calculated resistance for each of the 3 models used. G5 ventilator employs a higher bias flow as expected, but more interestingly imposes less resistance to exhalation than the Servo U. Some measures suggest that increasing PEEP does increase the imposed expiratory resistance.

Sample Waveforms
Term model: Top panel, sample pressure and flow tracings - Airway
Bottoms panel: sample flow tracings - Inspiratory limb of circuit