2004 OPEN FORUM Abstracts
RESPONSE OF THE VENTILATOR SUBSEQUENT TO PATIENT DISCONNECTION DURING DUAL-MODE VENTILATION
Essam
Aljamhan RRT,1 David Southwick,2 Lonny J.
Ashworth MEd RRT2. King Abdulaziz Medical City,1
Boise State University, Boise, ID.2
Background:
In dual-mode ventilation, each breath is a pressure-limited
breath in which the pressure level is automatically modulated to
achieve a preset tidal volume (VT).The ventilator will
deliver a single volume-controlled test breath with a constant flow
waveform to determine the compliance and resistance when the patient
is initially connected to the ventilator. After the compliance and
resistance have been measured, the ventilator adjusts the pressure
required to deliver the set VT. Subsequent breaths are
delivered as pressure-targeted breaths. The inspiratory pressure is
based on the resistance, compliance, set VT and patient
effort. If the delivered VT varies from the preset value,
the target pressure for subsequent breaths is adjusted incrementally
to achieve the set tidal volume.
Study
Question: What is the response of various ventilators to a
patient/ventilator disconnection while in dual-mode ventilation?
Method:
Three ventilators were studied: Viasys Avea (VA), Drager Evita 2
(DE) and Puritan Bennett 840 (840). The values for Peak Inspiratory
Pressure (PIP), Inspiratory VT (VT insp) and
Expiratory VT (VT exp) displayed on the
ventilators were recorded while connected to a mechanical lung model.
Ventilator settings: Modes tested were Dual-Mode Assist-Control and
Dual-Mode SIMV; VT 500 mL; TI 0.84 - 0.85
seconds; PEEP 0.0 cm H2O; respiratory rate 12 breaths per
minute. Each ventilator was disconnected for 10-15 seconds then
reconnected; the values for PIP, VT insp, and VT
exp were recorded until values stabilized.
Results:
With a measured compliance of 20 mL/cm H2O and
resistance of 5-7 cm H2O/L/sec, the PIP for each
ventilator was as follows: VA 25 cm H2O, DE 28 cm H2O,
840 28 cm H2O. After disconnecting and then reconnecting
the ventilator to the mechanical lung model, the 840 ventilated at
the previous pressure required to deliver the set VT prior
to the disconnection. The VA delivered a low PIP (4-6 cm H2O)
for the first breath, but on the second breath the PIP increased to
the previous level prior to the disconnection. The PIP varied
slightly for 4 – 5 breaths before the VT stabilized
at the set value. The DE started with a test breath of 6-9 cm H2O,
resulting in a VT of 65 - 69 mL on the first breath. With
every breath following the test breath, the PIP increased by no more
than 3 cm H2O until the preset VT was reached;
this required 11 – 12 breaths.
Conclusion:
After sensing a patient disconnection during dual-mode ventilation a
significant difference between the three test ventilators was noted.
The Drager Evita 2 was the only ventilator that ventilated with an
initial test breath, and then incrementally increased the pressure by
no more than 3 cm H2O until the set VT was
reached. The Viasys Avea and PB 840 started at the pre-disconnection
pressure required to deliver the set VT during the first
or second breath after reconnection to the lung model. Clinical
trials are necessary to assess the significance on patients of a
disconnection or of a change in compliance between disconnection and
reconnection of the ventilator when utilizing dual-mode ventilation.