2004 OPEN FORUM Abstracts
VENTILATORY RESPONSE DURING DUAL-MODE VENTILATION AFTER REMOVAL OF A FIBEROPTIC BRONCHOSCOPE.
Nikolas Sirs,
Ross Armstrong, Lonny Ashworth MEd RRT. Boise State University,
Boise, ID.
Background: When
an intubated patient has a bronchoscopy performed, the airway
resistance increases substantially while the bronchoscope is
inserted. If a patient is being ventilated in dual-mode ventilation,
the peak airway pressure must increase to deliver the desired volume.
Once the bronchoscope is withdrawn, the resistance abruptly decreases
and the ventilator reduces the pressure to a lower level to deliver
the desired volume. The purpose of this study was to evaluate the
response of three ventilators during simulated bronchoscopy.
Method: Three
ventilators were evaluated: Drager Evita 2, Puritan Bennett 840,
Viasys Avea. Each ventilator was connected through the same circuit
with an 8.5 mm endotracheal tube to a mechanical test lung (TTL). The
TTL compliance was 0.03 L/cmH2O; resistance was 20 cm
H2O/L/sec. Ventilator settings were: Dual-mode,
assist-control; VT 500 mL; respiratory rate 12/minute; I:E
1:3; PEEP 0 cm H2O. All alarms and limits were set to
extremes. After the ventilator equilibrated at the 500 mL target, a
6.0 mm catheter was passed into the ETT, simulating a bronchoscope.
The ventilators were allowed to readjust the pressure to reach the
500 mL target, then the catheter was removed. Peak pressure and VT
were recorded for every breath until pressure and volume were stable.
Each ventilator was tested five times.
Results: After
removal of the catheter, the Viasys Avea delivered one breath at the
same pressure as that reached with the catheter inserted, resulting
in an elevated VT. On the second breath the pressure
decreased to the level prior to the insertion of the catheter. Minor
changes in pressure resulted on subsequent breaths, reaching the
desired VT. Both the Puritan Bennett 840 and the Drager
Evita 2 delivered one breath at the pressure reached with the
catheter inserted, resulting in an elevated VT, then
decreased the pressure by no more than 3-4 cm H2O per
breath causing large VT after the catheter was removed for
up to ten breaths.
Conclusion: Each
ventilator responds somewhat differently during dual-mode
ventilation. Without the proper maximum volume alarm settings and
limits, dual-mode ventilation could result in unacceptably high
airway pressure and tidal volume during a bronchoscopy or similar
events when a severe obstruction is added and then removed. The Avea
responded the quickest by delivering only one unsuitable pressure and
volume, compared to the multiple breaths it took the other
ventilators to respond.