Biphasic positive airway pressure
Synonyms and keywords: BPAP, variable positive airway pressure, bilevel positive pressure airway

# Overview
Bilevel positive airway pressure (BPAP) is a continuous positive airway pressure (CPAP) mode used during noninvasive positive pressure ventilation. It delivers a preset inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP).  BPAP can be described as a continuous positive airway pressure system with a time-cycled or flow-cycled change of the applied CPAP level.. Another term for bilevel positive airway pressure, and the term becoming increasingly adopted by the medical community, is non-invasive positive pressure ventilation (NIPPV) or non-invasive ventilation (NIV).

# Historical Perspective
Biphasic/bilevel as a mode of ventilation was first presented in 1988 by Professor Benzer of Innsbruck and his group. His theory consisted of alternating PEEP levels. This was the first time the acronym BIPAP was used and was followed in 1989 with the publication of a new approach to ventilatory technique by Baum & Benzer which was also the first full year of commercial introduction of "Biphasic Positive Airway Pressure" as an integrated mode of ventilation on the Evita ventilator.  This concept was introduced as a positive adjunct to weaning from ventilator support.

# Mechanism
BiPAP refers to maintaining constant airway pressure during both inspiration and expiration. This is a variant of Pressure Control ventilation in which  the patient can breathe in and out during any phase of respiration. Common BiPAP modes have the ventilator synchronise both inspiration and expiration to patient effort.  Inspiration usually commences on detection of a patient-generated trigger (typically flow or pressure).  The ventilator switches to expiration when the flow rate during inspiration falls below the peak flow rate (tyically below 25% of peak flow).

# Differentiating BPAP from Other Pressure Airways
Continuous positive airway pressure (CPAP), is a positive pressure airway in which a constant flow of air is provided via a face mask. The pressure of this air is determined based on needs of the patient and the condition. This airway has a continuous pressure where as BPAP has two different pressures which machine alternates by itself during inspiration and expiration.

# Uses
BPAP and other non-invasive ventilation modes have been shown to be effective management tools for chronic obstructive pulmonary disease and acute respiratory failure.
Bilevel positive airway pressure is used when positive airway pressure is needed with the addition of pressure support.  Common situations where positive airway pressure is indicated are those where taking a breath is difficult.  These include pneumonia, chronic obstructive pulmonary disease, asthma and status asthmaticus.

# Advantages
The advantages of BiPAP/Pressure Support are
- Patient can breathe spontaneously; paralysis not always required
- Optimum continous pressure during inspiration reduces work of breathing
- CO2 levels are generally lower than without support
- Intrapleural pressure generally not as high as for intermittent positive pressure ventilation(IPPV) so less depression of cardiac output.