GE iVent 201 Series, User'S Reference Manual

Page: 247 / 290

Appendix F: Hold Function and Static Mechanics Measurements
235
FRONT PANEL CONTROLS
The Hold Button has two functions. Pressing it results in the following:

Pressed once initiates an end inspiratory hold maneuver which allows the
calculation of static compliance (See Static Compliance Measurements, page
235). This maneuver should be administered by clinicians who are
knowledgeable about the effect on the patient of this maneuver.

Pressed twice in succession initiates an end expiratory hold maneuver which
allows the calculation of intrinsic PEEP. This maneuver should be
administered by clinicians knowledgeable about the effect on the patient of
this maneuver.
Pressing the Hold or Clear button when either an inspiratory hold or an
expiratory hold maneuver has been initiated cancels the maneuver.
STATIC COMPLIANCE MEASUREMENTS
Certain versions of the iVent
TM
201 ventilator (version 1.4 model iVent
TM
201 MRI IC
1.4 M1171648 and higher only) are capable of measuring static pulmonary
mechanics through the addition of a special control mechanism for the
exhalation valve.
Two types of static respiratory measurements are available to the user of the
iVent
TM
201 ventilator – Static Compliance using end inspiratory hold, and Auto
PEEP using end expiratory hold. Due to the fact there is resistance in airways,
there is a delay to the equilibration of pressure throughout the respiratory
system. In order to characterize tissue properties of the respiratory system
independently of airway resistance, it is necessary to stop airflow for a period of
time long enough for the pressure in the respiratory system to become equal. The
ability to perform either of these static measurements therefore requires that the
exhalation valve be actively controlled so that it remains closed during the
relevant portion of the breath.
STATIC COMPLIANCE
During a static compliance measurement, the ventilator senses when the end of
inspiration occurs and blocks the exhalation valve so that no air can escape the
lung. Once the exhalation valve is closed, the airway pressure distributes across
the various resistances of the respiratory system until the lungs are at the same
pressure as the airway. At this point, the pressure is recorded (plateau pressure)
and the exhalation valve is released and the patient is allowed to exhale. Static
compliance is then calculated as the volume exhaled following release of the end
inspiratory hold maneuver divided by the change in pressure from the plateau
pressure to PEEP. The average value for plateau pressure is also displayed in the
Show Mechanics option (See page 119)