Reliability of Tidal Volume in Average Volume Assured Pressure Support Mode

Abstract

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.

Keywords: average volume assured pressure support mode; bi-level; home mechanical ventilation; noninvasive ventilation.