The Science Journal of the American Association for Respiratory Care
Background: Advances in mechanical ventilator design are allowing accurate flow delivery to meet the ventilatory needs of neonatal to adult patients. We designed this study to evaluate the accuracy of a prototype flow controller for such a ventilator design (Thermo Respiratory Group) compared to a commercially available ventilator of such a design (Siemens Servo 300).
Methods: Each ventilator was set to deliver a tidal volume range of 2 mL to 2000 mL and a flow range of 0.4 L/min to 150 L/min. Compliance and resistance of the lung model were varied (resistance of 500 cm H2O/L/s and compliance of 1 mL/cm H2O at 2 mL and 0.4 L/min; resistance of 5 cm H2O/L/s and compliance of 50 mL/cm H2O at 2000 mL). The FIO2 was held constant at 0.6 and FIO2 was continuously measured. Volumes were measured by accumulating 10 to 2400 breaths (fewer breaths for higher volumes) into a water-sealed Tissot spirometer. Reference volumes were calculated by dividing the total volume collected by the number of breaths. During use of the Servo 300, a correction for the bias flow of 0.5, 1.0, and 2.0 L was made. Volume error was calculated as the difference between set and actual volume divided by set volume. A paired t-test was used to determine statistical significance.
Results: The table shows data for representative points along the range of volumes tested.
|6 mL||20 mL||50 mL||100 mL||480 MI||1000 mL||2000 mL||Mean ± SD|
|Thermo||0.85||-0.07||-0.07||-0.07||-1.0||-0.7||0.35||-0.10 ± 0.6*|
|Servo||4.9||2.41||-1.95||-3.06||-1.82||-0.75||-1.03||-2.23 ± 1.3|
|*p = 0.005 Thermo vs Siemens|
Conclusion: Both ventilators deliver flows accurately across a wide range of tidal volumes. The % error is well within clinically acceptable ranges. Delivered FIO2 was unaffected. The differences in % error were statistically significant. Further research would be required to determine if these differences had clinical implications.