2004 OPEN FORUM Abstracts
VENTILATORY RESPONSE DURING DUAL-MODE VENTILATION AFTER REMOVAL OF A FIBEROPTIC BRONCHOSCOPE.
Ross Armstrong, Lonny Ashworth MEd RRT. Boise State University,
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 Once the bronchoscope is withdrawn, the resistance abruptly decreases and the ventilator reduces the pressure to a lower level to deliver the desired volume.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.