Predictive modeling of the performance of the Zoll Z Vent® under hyperbaric conditions

Prior work demonstrated challenges with ventilators in the hyperbaric environment; few ventilators are fully equipped to address these concerns. We hypothesized the Zoll Z-vent® would deliver set tidal volumes incorrectly in volume control mode, but we could correct it using an algorithm. We used the Zoll Z-vent® in assist control mode in a Class A multiplace chamber and the Michigan test lung system. We identified the set tidal volumes on the ventilator that were necessary to achieve target tidal volumes at various depths. We graphed set tidal volume as a function of depth and performed linear regression modeling. From the regressions, we graphed the slope of each versus the target tidal volume and performed a second set of regressions. We generated an equation from our data to predict set tidal volumes. Set tidal volumes necessary to deliver target tidal volumes were directly proportional to depth in a linear manner. The slope of the regressions as a function of target tidal volume was also linearly proportional. The slope of the second set of regressions generated an equation that is used to predict set tidal volume for a given target tidal volume, PEEP, and gas. The Z-vent® can safely deliver mechanical ventilation under hyperbaric conditions with correction using our model. We use a spreadsheet to calculate set tidal volume for any given depth in clinical practice. We have internally validated this model on over 100 patients with multiple quality control measures in place.