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Charles Gomersall
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Ventilator delivers two levels of positive airway
pressure for preset periods of time
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Airway pressure release ventilation (APRV) is a form of
BIPAP in which the duration of the low pressure period ≤1.5 seconds
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Patient is able to take spontaneous breaths at both
high and low pressure levels
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In general these spontaneous breaths do not result
in a change from low pressure to high pressure, except when the breath
is taken close to the time when the ventilator is due to cycle from low
to high pressure. In this circumstance the shift from low to high
pressure is synchronized with the patient’s inspiratory effort.
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spontaneous breaths may be assisted by adding
pressure support but there is little evidence to support this practice.
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Oxygenation is determined by the inspired oxygen
concentration and the mean airway pressure
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Carbon dioxide elimination is dependent on the
difference between high and low pressures, the frequency of cycling between
high and low pressures and the patient’s spontaneous breaths.
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Important to set the lower pressure at a level that
ensures maximum lung compliance, particularly if spontaneous breaths are not
assisted
Advantages
- decreased requirement for sedation
- improved ventilation to dorsal areas of lung in patients taking
spontaneous breaths - probably due to diaphragmatic contraction opposing
alveolar collapse
- improved ventilation perfusion matching in patients with ARDS who are
taking spontaneous breaths. Associated improvement in oxygenation is slow,
occurring over 24 hours
Disadvantages
- theoretical risk of over-distension of lungs because patient can
take a breath when lung is already inflated
Further reading
Putensen
C, Wrigge H. Clinical review: Biphasic positive airway pressure and
airway pressure release ventilation. Critical Care, 2004; 8(6):492-7
Page created 8th March 2006, updated October 2006
© Charles Gomersall 2006 |
