2004 OPEN FORUM Abstracts
COMPARISION OF DUAL MODE VENTILATION AMONG SELECTED ADULT CRITICAL CARE VENTILATORS USING A PROGRAMMABLE LUNG SIMULATOR
Ghazi
Alotaibi, MS, RRT (University of Medicine and Dentistry of New
Jersey, Newark, NJ); Robert Kacmarek, PhD, RRT, FAARC (Massachusetts
General Hospital and Harvard Medical School, Boston, MA); Craig
Scanlan, EdD, RRT, FAARC (UMDNJ, Newark, NJ); Al Heuer,
PhD, RRT (UMDNJ, Newark, NJ).
BACKGROUND: Dual mode ventilation (DMV) is a variant of PCV in which the
inspiratory pressure is adjusted breath-to-breath to accommodate
changes in respiratory mechanics, with the goal a more stable minute
volume. Currently, there are several adult critical care ventilators
that provide DMV. Although it is assumed that this mode operates in a
similar manner among these ventilators (Branson, Johannigman,
Campbell & Davis, 2002), no one has empirically tested this
proposition. To address this lack of knowledge, we compared the
performance of four adult critical care ventilators set to deliver
DMV using a programmable lung simulator. We hypothesized no
significant differences among ventilators on any of 11 measures of
respiratory mechanics during conditions of varying patient demand and
impedances.
METHOD: The Active Servo Lung 5000 (Ingmar Medical,
Pittsburgh, PA) simulator was programmed to produce 5 breathing conditions (a)
normal resistance and compliance (baseline), (b) low compliance, (c) high resistance,
(d) high patient demand, and (e)
simulated leak. The DMV feature of the Puritan-Bennett 840 (PB840),
Hamilton Galileo (Galileo), Drager Evita XL (Evita), and Siemens
Servo 300 (Servo) ventilators was implemented using the following settings VT =
600mL, Ti = 1 sec, PEEP = 4 cmH2O,
flow trigger = 2 L/min, and most rapid rise time. Ventilation
parameters were acquired, stored, and analyzed using the ASL5000
software. Dependent variables included inspiratory trigger airway
pressure (Pawt), trigger delay time (Dtrig), post-trigger delay time
(Dptrig), total trigger delay time (Dtot), patient inspiratory work
(Winsp), patient trigger work (Wtrig), inspiratory trigger muscle
pressure (Pmust), inspiratory time 90% (IT90), VT, PIFR,
and PIP.
RESULTS: Due to the high precision of the ASL 5000
measurements, we adopted a decision rule requiring variations in
excess of 2 SD from the group mean to be considered of ‘practical’significance.
At baseline, the Evita imposed higher Wtrig and Dtot than the other ventilators.
When compliance was low, the Galileo
exhibited longer delay times and higher work parameters that its
counterparts. When resistance was high, the Evita imposed higher work
and longer delay times than the Galileo, Servo or PB840. When patient
demand and system impedances were increased, both the Galileo and
Evita imposed higher Wtrig and Pmust than either the PB840 or the
Servo. In comparison to the other ventilators, the Servo
underperformed (more work and less synchrony) during the simulated
leak test. The Galileo had the highest VT delivery under
all conditions.
CONCLUSIONS: The assumption that DMV operates in a
similar manner across adult critical care ventilators is not
supported. The PB840 appears to offer the best overall synchrony and
lowest imposed work. The Galileo and Evita imposed more work and
exhibited variable synchrony under different tested conditions. These
differences in performance during DMV are likely due to variations in
the underlying algorithms used by each ventilator and/or the
technical attributes of their sensor and measurement systems.