Reliability of Tidal Volume in Average Volume Assured Pressure Support Mode

BACKGROUND: Remote monitoring is increasingly used in patients who receive home mechanical ventilation. The average volume assured pressure support mode is a target volume pressure preset mode that delivers a given tidal volume (V-T) within a range of controlled inspiratory pressures. In a mode such as this, it is important to verify that the V-T value retrieved from the ventilator SD card is accurate. METHODS: A lung model was set with C (Compliance) 0.075 L/cm H2O and R-I (Inspiratory resistance)-R-E (Expiratory resistance) 15-25 cm H2O/L/s (model 1) or with C 0.050 L/cm H2O and R-I 6 cm H2O/L/s (model 2) and 6 cm H2O effort. Three home-care ventilators (A40, PrismaST30, and Vivo40) were set to average volume assured pressure support mode with 0.3 and 0.6 L V-T each at PEEP 5 and 10 cm H2O, and were connected to the lung model with and without nonintentional leak. The reference airway pressure and flow were measured by a data logger. V-T was expressed in body temperature and pressure saturated. We assessed the difference in V-T between the ventilator SD card and a data logger relative to set V-T and factors associated with its magnitude. RESULTS: For A40, PrismaST30, and Vivo40, the adjusted mean V-T differences between the ventilator SD card and the data logger were -0.053 L (95% CI -0.067 to -0.039 L) (P < .001), -0.002 L (95%CI -0.022 to 0.019 L) (P = .86), and -0.067 L (95% CI -0.007 to 0.127 L) (P = .03), respectively. The partial Spearman correlation coefficients between the ventilator SD card and a data logger were 0.89 (P < .001), 0.59 (P < .001), and 0.78 (P < .001), respectively to the ventilators. The relative variations in measured V-T from the set V-T were 16.0, -12.0, and 6.7% for the ventilator SD card, and were -2.5, -7.5, and -27.2% for the data logger, respectively. The discrepancy in ventilator between SD card and data logger were influenced by PEEP for the PrismaST30 ventilator, nonintentional leak for the Vivo40 ventilator and PEEP, nonintentional leak, and underlying disease, the effect of each depending on the levels of the other factors, for the A40 ventilator. CONCLUSIONS: In the 3 home-care ventilators, the ventilator SD card underestimated V-T. Factors involved in this difference differed among the ventilators.