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Up Assist control BIPAP

Charles Gomersall

  • Ventilator delivers two levels of positive airway pressure for preset periods of time

  • Airway pressure release ventilation (APRV) is a form of BIPAP in which the duration of the low pressure period ≤1.5 seconds

  • Patient is able to take spontaneous breaths at both high and low pressure levels

    • 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.

    • spontaneous breaths may be assisted by adding pressure support but there is little evidence to support this practice.

  • Oxygenation is determined by the inspired oxygen concentration and the mean airway pressure

    • Mean airway pressure can be increased by increasing both the high and low pressures or by increasing the time at high pressure

  • 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.

  • Important to set the lower pressure at a level that ensures maximum lung compliance, particularly if spontaneous breaths are not assisted


  • 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


  • 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

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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