1998 OPEN FORUM Abstracts
PRESSURE ASSIST AS A FORM OF PATIENT TRIGGERED, PRESSURE TARGETED VENTILATION.
Robert McConnell, RRT and Neil MacIntyre, MD, Duke University Medical Center, Durham NC
Pressure Assist (PA) is a patient triggered, pressure targeted, time cycled form of ventilatory support. We reasoned that this type of support could be used as an alternative to pressure support (PS) under circumstances when clinician set time cycling could offer better patient synchrony than the automatic flow cycling of pressure support. Accordingly, we designed a study to measure patient ventilatory patterns, oxygenation and inspiratory effort during PA and compared them to PS. Our hypothesis was that providing PA with an inspiratory time (Ti) comparable to PS would have no effect but that shortening or extending the Ti would induce changes in both effort and ventilatory pattern. Nine ventilator dependent patients receiving stand alone PS (mean setting of 16.8 cmH2O) were recruited for the study. The test protocol included baseline measurements on PS and then supplying PA at the same inspiratory pressure but with the set Ti adjusted to match the Ti of PS, exceed the Ti of PS by 0.3 sec and be below the Ti of PS by 0.3 sec. At each setting, tidal volume (VT), frequency (f), pulse oximetry (SpO2), and the maximal esophageal pressure generated (Pes) were recorded. ANOVA was used to assess statistical differences in the various PA settings vs. PS. Our results showed no significant differences in any measurement when the set Ti during PA matched the observed Ti of PS. However, there were significant increases in VT and decreases in f as the set Ti of PA was increased. Moreover, there was a trend that did not reach statistical significance towards lower Pes values as the set Ti was increased (TABLE).
PA (short Ti) PA (Ti=PS Ti) PA (long Ti)
VT (vs PS) -102+/-109* +36+/-52 +102+/-95*
f (vs PS) +5.2+/-3.6* -1.8+/-2.8 -6.2+/-3.3*
SpO2 (vs PS) -.6+/-2.5 -.1+/-1.7 +.5+/-1.3
Pes (vs PS) +.25+/-.5 -.9+/-1.3 -1.3+/-1.1
* P < 0.05 compared to PS
We conclude that PA is an alternative form of patient triggered, pressure targeted ventilation that is time cycled. It has similar effects to PS when the Ti is comparable. The ability to change Ti with PA, however, may offer an advantage over PS in patients in whom breath cycling dys-synchrony exists.
The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.