A BiPAP machine delivers pressurized air that can keep the airway to the lungs open. It pumps air at two different air pressure levels, one for breathing in (IPAP) and another for breathing out(EPAP). They are set after assessing patients condition and type of disease. IPAP is basically the positive airway pressure that we give in inspiration and EPAP is expiratory positive airway pressure that prevents our alveoli from collapsing and keep them open. BiPAP basic modes are S, St and T.

In these machines, two fixed air pressure levels — one for breathing in and one for breathing out — are determined by a doctor and programmed into the device. These two levels do not change during the night. 

 An auto-adjusting BiPAP machine has a range set for both IPAP and EPAP. This allows the machine to adjust automatically throughout the night in response to how the sleeper is breathing.

In S mode all the breaths are patient triggered and cycled. Machine delivers pre set pressure during inspiration and expiration. No automatically delivered breath is inhaled. Pt initiate all the breaths and machine respond to inspiration and expiration.

 In T mode machine does not rely on patient breath triggering effort. All the breaths are automatically delivered and set. So it is a machine cycled and machine triggered mode.

 In S/T mode breaths are patient triggered and machine trigerred, patient cycled and machine cycled. We set backup breaths and also Ti. If patient do not initiate the breath during the set time then machine automatically delivers the breath.

APCV - Assisted Pressure Control Ventilation. 

The APCV Mode is used for assisted pressure control ventilation at a fixed mandatory ventilation rate. In case of spontaneous respiration, the patient has the possibility of increasing the rate and consequently the minute volume. If the patient displays a spontaneous respiratory effort within a specified time slot of the expiration, the mandatory mechanical breath is synchronized with the patient's respiration.

APCV mode is particularly for critical patients who has rapid and shallow breathing (high frequency breathing) and low tidal volume. It is used to get the targeted tidal volume, mainly used in hospitals.

We suggest patients to use ST mode after leaving the hospital, and don't use APCV mode for a long time.

Tidal Volume (symbol VT ot TV) is the amount of air that moves in or out of the lungs with each respiratory cycle. It measures around 500 mL in an average healthy adult male and approximately 400 mL in a healthy female. It is a vital clinical parameter that allows for proper ventilation to take place. When a person breathes in, oxygen from the surrounding atmosphere enters the lungs. It then diffuses across the alveolar-capillary interface to reach arterial blood. At the same time, carbon dioxide continuously forms as long as metabolism takes place. Expiration occurs to expel carbon dioxide and prevent it from accumulating in the body. The volume of inspired and expired air that helps keep oxygen and carbon dioxide levels stable in the blood is what physiology refers to as tidal volume

Minute ventilation = respiratory rate x tidal volume

Minute Ventilation (MV or VE) is an important measurement that's related to tidal volume. It's a measurement of the volume of inhaled and exhaled air over 60 seconds. A typical adult VE ranges around 4 to 6 liters in 60 seconds.

You can increase your VE by either taking deeper breaths (increasing Vt) or by breathing faster (increasing your respiratory rate).

• BiPAP Is a Better Treatment for Those With Breathing Restrictions.
• BiPAPMakes Exhaling Easier—Which Is Good for Those With a Need for a Higher Inspiratory Pressure.
• BiPAP Includes an Optional Breath Timing Feature.

BiPAP machines are complex and have more parts and features that need to come together for the wearer in comparison to CPAP and APAP machines. Its motor and air control technologies must be able to regulate two pressure levels for your every breath with little room for error. Therefore, not only is the underlying technology more expensive to produce, but it must also be made of more durable material to withstand the constant ebbing and flowing of air pressure.