1997 OPEN FORUM Abstracts
COMPARING VENTILATOR TIDAL VOLUME DELIVERY AND MEASUREMENT IN TWO BRANDS OF MECHANICAL VENTILATORS.
Jim Keenan BS, RRT, John Salyer BS, RRT, Kaylene Christensen RRT, Stephanie Jemmett RRT. Primary Children's Medical Center, Salt Lake City, Utah.
Introduction: We sought to determine if there were differences in the delivery and measurement of Vt in two brands of ventilators. Methods: Servo 900 C (n=9) and Bird V.I.P. ventilators (n=16) were tested from our working fleet. All were functioning normally, maintained and calibrated according to manufacturer's guidelines. Testing was done in a volume-limited mode with a set Vt of 1000 mL, while ventilating a Michigan TTL test lung with the compliance set at [approx] 0.010 L/cm. A 2 ft tygon test circuit was used to minimize compressible volume loss. A leak check was performed on the entire system before each run. Vt was recorded after two minutes from the intrinsic measurement mechanism of each ventilator and by a computerized pneumotachograph at the airway opening (Ventrak). Accuracy of the Ventrak was verified using 100 and 1000 mL Hans Rudolph calibration syringes. Differences in Vt measurements were tested for statistical significance (P < 0.05) using ANOVA. Results: For the Servo ventilators we found statistically significant differences in Vt between the ventilator's measurement system and the Vt reported from the Ventrak. Conversely, the differences between the Vt's measured by the VIP and by the Ventrak were not statistically significant. There were also statistically significant differences in Vt measured by the Ventrak when comparing the 900 C and VIP.
(See original for figure)
Discussion: Our data suggests that the performance of the intrinsic Vt measuring system of the 900 C ventilators is very poor when compared to the VIP ventilators. Assuming the Ventrak readings to be the true Vt, it is also clear that the VIP ventilators deliver a larger Vt than the 900 C under large Vt and poor compliance conditions, although this difference may not be clinically important.