458 - Balancing Ventilation in Heterogenous Lung Disease – A Simulated Bronchopulmonary Dysplasia (BPD) Examination of Ventilator Strategies

Poster Number: 458
Publication Number: 458.229

Shafeeque Kunhiabdullah, Case Western Reserve University School of Medicine, north ridgeville, OH, United States; Allison Peluso, Cleveland Clinic Children's, Cleveland, OH, United States; Robert Chatburn, Cleveland Clinic, Cleveland Heights, OH, United States; Ibrahim Sammour, Cleveland Clinic Children's, Beachwood, OH, United States

Background: BPD is a heterogeneous lung disease with varying regional time constants. This poses a challenge when ventilating premature infants. Our lab has previously demonstrated that prolonging the inspiratory rise time (IRT) in pressure control ventilation improved volume balance (VB%) at the cost of delivered tidal volume (VT).

Objective: To evaluate how volume balancing measures such as increased I-time and driving pressure influence VB% while changing IRT.

Design/Methods: A passive dual-chamber lung model was constructed using the IngMar ASL5000 to approximate moderate BPD in a 4 Kg infant. One chamber had a short time constant (STC), and the other had a long time constant (LTC), (Fig 1). A Servo-I ventilator was used to provide adaptive pressure controlled continuous mandatory ventilation (PC-CMVa - PRVC) to maintain VT. The rate was set to 30 breaths per minute, target tidal volume was set to 32mL, PEEP was set to 5 cm H2O. 9 sets of experiments were conducted using combinations of IRT of 0 ms, 100 ms, and 200 ms, matched with I-times of 0.4 s, 0.5 s, and 0.6 s. The driving pressure from the ventilator was allowed to equilibrate over the initial 30 breaths. A minimum of 210 consecutive breaths/experiment were obtained. Data from 100 consecutive breaths were analyzed & processed at BTPS (Body Temperature, ambient pressure, and gas saturated with water vapor) conditions using the ASL5000 software. Outcome variables were peak inspiratory flow rate (PIFR), peak pressure (PeakP), total-PEEP, and chamber specific VT. VB% was computed as (VTLTC-VTSTC)/VTTotal X 100%. Linear regression & scatterplots were used to assess the impact of changing IRT, I-time, and driving pressures on the variables (Minitab 20).

Results: In this model, there was no significant total -PEEP build-up and delivered VT were within 5% of set. As expected in a volume targeted scheme, increasing IRT and I-time both decreased PIFR, while shortening IRT and prolonging I-time generated lower PeakP (Fig 2a-d). Interestingly while the VTTotal was relatively maintained, a shorter I-time and a longer IRT favored VT delivery to the STC chamber at the expense of VT delivery to the LTC chamber. This improved the discrepancy between these chambers as measured by a decreasing VB% (Fig 3 a-c).Conclusion(s): In a heterogenous lung with varying time constants, reducing the I-time to trim the tail-end of flow & prolonging the IRT, while allowing the ventilator to increase driving pressure to maintain VTTotal can decrease the VB% (fig 3 d-e).
Fig 1: ASL5000 Lung ModelTwo chamber lung model of moderate BPD with a short time constant and a long time constant
Fig 2: Impact of changing I-time and IRT on PEEP, Tidal Volume, PIFR, and Peak Pressurea) PEEP remains reasonably unchanged when modifying I-time and IRT
b) Delivered tidal volume remains reasonably constant when modifying I-time and IRT
c) As expected, at a relatively constant tidal volume, PIFR decreases with increasing I-time and increasing IRT
d) As expected, at a relatively constant tidal volume, peak pressure decreases with increasing I-time, and increases with increasing IRT