This article will explain the fundamental differences between BiPAP machines and CPAP machines and the reasons one might choose to use a BiPAP machine over a standard CPAP machine. I'll also take a look at the specific features offered by a few of the most prevalent BiPAP machines being offered today, including the Respironics BiPAP Auto M Series.

Bilevel CPAP machines - commonly referred to as BiPAP machines - provide the most flexibility with regard to exhalation pressure relief. A bilevel CPAP system delivers two different positive pressure levels - an inspiratory positive airway pressure, or IPAP, and an expiratory positive airway pressure, or EPAP. The difference between these two pressure levels is commonly referred to as the pressure support.

This type of pressure relief is similar to pressure relief technologies like C-Flex, EPR, and SoftX, with the primary difference being that the pressure support on a bilevel CPAP machine can be much higher. That is, the difference between the IPAP and EPAP on a bilevel machine can be much greater than the difference you might experience using one of the aforementioned pressure relief technologies.

So the question becomes, ""who is a candidate for a BiPAP machine?"". In general anyone with a relatively high CPAP pressure setting is a candidate for bilevel therapy. For example, if a CPAP user is prescribed a CPAP pressure setting of 16 cm H2O, then the maximum pressure support (or pressure relief) you could expect to experience with a technology like C-Flex is a drop of approximately 3 cm H2O, leaving you with the task of exhaling against a pressure of 13 cm H2O. For some CPAP users, an exhalation pressure of 13 cm H2O is uncomfortable. For others, it's simply just not possible.

With a BiPAP machine, this same CPAP user can have an inhalation pressure of 16 cm H2O and have an exhalation pressure that is extremely low, even all the way down to 4 cm H2O. In this case, the CPAP user gets the pressure required to prevent apneas, hypopneas and snoring, but doesn't have to suffer the effects of a high level of pressure during exhalation. You just can't get that kind of pressure relief with a standard CPAP machine.

In addition to the pressure support (i.e. pressure relief) offered intrinsically through the difference between IPAP and EPAP pressure levels, you may also hear about an additional pressure relief feature called Bi-Flex. Bi-Flex is similar to C-Flex and is found on new BiPAP machines manufactured by Respironics. Bi-Flex allows for a decrease in the EPAP level. You may now be wondering why one would use Bi-Flex in addition to an EPAP level that is already significantly lower than the IPAP level. Why not just lower the EPAP level even more? The answer to this is that Bi-Flex can be unlocked during the setup process to make it adjustable by the CPAP user. This gives the CPAP user a little room for tweaking the EPAP level if necessary. If you want some control over your expiratory positive airway pressure level, then a feature like Bi-Flex is for you.

The BiPAP Auto M Series from Respironics is an example of a bilevel CPAP machine that adjusts automatically throughout the night. Rather than programming specific IPAP and EPAP levels, the clinician or supplier will program the bilevel machine for a maximum IPAP and a minimum EPAP. Much like the more common automatic CPAP machine, the automatic bilevel machine senses the breathing of a CPAP user on a breath-by-breath basis and automatically delivers the optimal pressure level. A maximum pressure support level can be programmed into the BiPAP Auto M Series, so that when the machine needs to ramp up to the maximum IPAP level, the delivered EPAP level will not necessarily be the pressure defined by the EPAP level setting, but it will be the IPAP level minus the pressure support level that is programmed into the unit.

The BiPAP Auto M Series can also be used as a regular BiPAP machine with fixed IPAP and EPAP levels, and it can be programmed to transition from the fixed pressure mode to the automatic mode after a certain period of time.

A slightly more sophisticated bilevel CPAP machine is one that has a ""spontaneous / timed"" mode or S/T mode. This type of machine is designed to deliver a machine-triggered breath if the CPAP user does not spontaneously breathe within a set period of time. The Respironics BiPAP S/T and the ResMed VPAP III are examples of CPAP machines that ensure the CPAP user receives a minimum number of breaths per minute.

CPAP-Supply.com currently sells the following bilevel CPAP machines:

  • Respironics BiPAP Auto M Series
  • Respironics BiPAP Plus M Series
  • Puritan Bennett GoodKnight 425
  • ResMed VPAP III

Feel free to call us for more information about BiPAP machines, the benefits of BiPAP therapy, and whether or not a BiPAP machine would be a good choice for you.

Andrew Senske

CPAP-Supply.com is a leading online retailer of CPAP equipment. Located in Spokane, WA CPAP-Supply.com has been serving thousands of customers around the world since 2001. Founded on a belief that patients are their own best primary care providers, CPAP-Supply.com understands the importance of educating patients and customers on both the effects of and treatment for obstructive sleep apnea. For more information visit CPAP-Supply.com or call toll free 1-888-955-2727.

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