Care, Maintenance, and Tests
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F.2 Static Compliance Measurements
Certain versions of the iVent
201
ventilator (version 1.4 model 502i2301-A0
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
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.
F.2.1 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.
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