Pressure Support Mode VS CPAP/BiPAP


I just started on a ICU floor and am super overwhelmed with information especially regarding vents. Almost every patient on the floor is on one so I know it is super important to understand them.

Can someone explain to me how the Pressure Support mode is different from CPAP/BiPAP?

Both modes seem to do the same thing, which is apply positive pressure during patient initiated breaths to decrease the work of breathing.

12 Answers


190 Posts

Specializes in GICU, PICU, CSICU, SICU. Has 6 years experience.


I'll give it a shot. CPAP is just continuous positive airway pressure. This means that the patients get a set amount of pressure (e.g. 5 cmH2O) applied to either his ETT or via mask. This 5 cm H2O gets applied regardless of inspiratory/expiratory efforts of the patient. There will always be 5 cm H2O applied. Conform the "rules" we speak of PEEP instead of CPAP when the patient has an ETT, and I will refer to PEEP after this. For this mode to work you need a conscious patient breathing in and out.

CPAP or just giving PEEP is mostly used in non-invasive ventilation where your patient has impaired oxygenation but can ventilate on it's own. A prime example would be someone in cardiogenic pulmonary edema. It will augment your patients oxygenation by keeping alveoli from collapsing and at the same time forcing some of the pulmonary edema back into the interstitium and keeping the edema localized. These patients have only a moderate alleviation of their work of breathing, but if you can get rid of the edema quickly enough your patient won't have to be intubated.

Pressure support is a mode where there is also a PEEP level set but the ventilator will deliver a preset pressure on top of this PEEP when it detects inspiratory efforts from the patient. This means for this mode you need to set at least two parameters (your PEEP and your pressure support level). And for it to work you need a breathing patient (so not heavily sedated).

Pressure control is used in the weaning phase of your patient where he does a lot of work himself to prepare him for the big bad world of breathing unassisted without a tube. It's also used during non-invasive ventilation when the problem is mostly respiratory failure due to muscle fatigue, loss of functional alveoli. Prime example is a COPD exacerbation that you want to keep from getting intubated (non-invasive) because part of their work of breathing comes from the added pressure support their muscles can rest a bit and recover for later when you DC the non invasive ventilation. Or the recovering patient that you are preparing to extubate (invasive).

Bipap stands for Biphasic positive airway pressure. When starting out I generally tell our newer colleagues to think of it as pressure control, but that's not completely right. I'll explain Bipap after explaining pressure control.

Pressure control is a mode where you apply a PEEP and an inspiratory pressure. The difference with pressure support is that you also add settings that determine when your patient will breathe in and out (e.g. frequency, I:E-ratio, etc.). Benefit of this mode is your patient has to do even less/no work breathing on their own and you can be sure that the machine will deliver its pressures when you want them to be delivered. Down side is your patient either needs to be sedated very well to allow the machine to determine when to breathe in/out or the patient's own breathing pattern will conflict with your predetermined settings and the patient will possibly fight against the machine.

An example would be your pneumonia patient that you intubated and you want to have him "rest" for a day (or two) as the antibiotics work their magic (you don't want to rest too long for fear of muscle wasting).

Most modern ventilators combine some form of pressure support and pressure control together so your patients gets X times per minute their pressure control mode but they can also trigger their own breathing that gets supported via pressure support in between. This leads to less fighting and discomfort for our patients, but can tire them out as well. I wish I could give you the terms but all different ventilator brands seem to have come up with even more creative names of naming all their modes.

I'm assuming you are using the Evita ventilator series. So Bipap in their system comes as either Bipap or Bipap/ASB.

Bipap is a "pressure control like ventilation" but instead of just delivering the pressure you set X times per minute it will allow a patient to breathe in/out on it's own (unassisted) on top of this inspiratory pressure level but also during the expiratory phase when there is just PEEP applied. So the idea is your patient fights less against the machine and will have less muscle wasting because he/she keeps using their breathing muscles.

Bipap/ASB is the same as Bipap but it will allow a pressure support (called ASB on an Evita) to be set as well. So when the ventilator detects inspiratory efforts from the patient it will give the ASB level of support instead of the inspiratory pressure you set for the pressure control part of the ventilator. During the expiratory phase when it gives its PEEP a spontaneous breathing attempt from the patient will also give them the ASB/pressure support level you set.

So Bipap has more diversity to it than simple pressure control. And you have different options. If you heavily sedate your patient that doesn't have their own breathing attempts your bipap becomes pressure control (you set PEEP, inspiratory pressure and frequency, and some other shizzle...). Since there are no attempts at breathing from the patient. It's pressure control.

If there is breathing but limited (and you didnt set an ASB/pressure support level) it will allow your patient to breathe in/out and regardless of this the machine will deliver its inspiratory pressure at X times per minute.

If the patient is breathing a lot (and you did set an ASB/pressure support) your patient will fall into a pressure support mode of ventilation doing more work themselves.

I hope this clears it up a bit. I can go on and on about vents but I'll keep it at that for now.


190 Posts

Specializes in GICU, PICU, CSICU, SICU. Has 6 years experience.

Bi-level is the competitor's name (I believe Maquet/Siemens) for Bipap from Evita

rkealy, BSN

45 Posts

Specializes in CCRN BSN Student FNP. Has 25 years experience.

It might be worth mentioning (if you didn't already know) that bipap increases ventilation which increases you PaO2 and decreases your CO2 while CPAP Primarily provides PaO2 support only:)


1 Post

FYI Pressure Control is not how you describe in regards to the weaning phase. What you are describing is pressure support for weaning. Pressure control is when there is a pre-set rate, so there is more assistance than there would be if patient was just on pressure support (pressure support patient has to depend on his/her own rate). (You later described this appropriately a few paragraphs down)



57 Posts

Speaking of vents (sorry OP to jack your thread), how much is too much for your patient to be breathing over the vent? I've had patients who were vented and did not look agitated yet were breathing upwards 30-40x a min when their respiratory rate on the vent was set at around 20-30. I once had to page a provider about giving better sedation because the abg for one of my patients came back terrible. We usually use PRVC mode here if anyone is familiar with that mode.

Specializes in Critical Care.
Speaking of vents (sorry OP to jack your thread), how much is too much for your patient to be breathing over the vent? I've had patients who were vented and did not look agitated yet were breathing upwards 30-40x a min when their respiratory rate on the vent was set at around 20-30. I once had to page a provider about giving better sedation because the abg for one of my patients came back terrible. We usually use PRVC mode here if anyone is familiar with that mode.

If they're breathing that frequently, and their ABG is bad, they should be getting more sedation or paralyzed.


79 Posts

Good description of modes above, but in general, Pressure Support is considered to be the same thing as CPAP/BIPAP except you give pressure support through a ventilator and BIPAP though Non-Invasive Ventilator (mask). At the alveolar level, a Pressure support of 10/5 is exactly the same as Bipap of 15/5 (weird difference is that the pressures on vents are additive (you add the 5 of PEEP to the 10 of pressure to get an inspiratory pressure of 10+5=15) while non-invasive the pressures listed are stand alone). All of these modes involve ASSISTING a spontaneously breathing patient by adding some pressure on top of the breaths they are already taking. If the patient isn't breathing themselves, it is best to use another mode (although it is possible to set both invasive and non-invasive on a higher rate to breathe FOR a patient, these situations are not common and take a provider who knows what they're doing to do correctly). Some people cross terms (in our unit they would always say that someone on a ventilator pressure support wean of 5/5 was on a "CPAP" wean... incorrect on several levels). So in general: Pressure support from the vent, BIPAP/CPAP from a mask, both are for patients who are spontaneously breathing but need a little extra support. Other info above was a good outline of the modes but I just wanted to add those so that you used the right terms at the right time!


27 Posts

Specializes in Critical Care Nursing. Has 2 years experience.

Colleagues have provided very good information on this. To follow up on PressG33's comments, CPAP is generally used for people with OSA. Not only does it provide a continuous positive pressure (like PEEP but we don't call it that if we are talking about non-invasive pressure support ventilation) which helps with oxygenation, but most importantly it opens the airways by increasing intrathoracic pressure and pushes the tongue forward which is of great help for those who have OSA. With CPAP, it doesn't matter how fast the patient is breathing or if they stop breathing, it will deliver that pressure all the time.

Bipap will deliver a different pressure depending on whether the patient is inhaling or exhaling. The pressure it gives when the patient is taking a breath is the inspiratory positive airway pressure IPAP, and expiratory positive airway pressure EPAP, when the patient breathes out. So, in a way it is like an assist mode on a ventilator with a set PEEP (would be the EPAP), and a pressure support (IPAP).


18 Posts

Has 3 years experience.

Not to get in-depth and scientific ...but when I'm at work if someone is on..

Pressure Support- They are intubated and the patient is on pressure support to see how well they tolerate doing the work of breathing on their own with the goal to extubate.

    [*=1]Generally, (with its exceptions) a patient will be on PS for few hours or so. This ventilator mode for long periods of time can tire a patient out.

BiPap- their pulmonary function is circling the drain... good chance this is the last step before they get intubated.

Cpap- In my experience this is used for someone with OSA. They wear it when they go to sleep and it comes off in the morning.

rkealy, BSN

45 Posts

Specializes in CCRN BSN Student FNP. Has 25 years experience.

I think of CPAP as a mode and pressure supports is the measurement of the amount of CPAP support. I also think a pressure support as peep I don't know if that's accurate but that's what I think of it . For instance you can have a non-invasive CPAP with a peep of 15 or you can be intubated on vent CPAP with a pressure support of 15. I know that's not completely Apples to Apples comparison but it's the way I think of it. BiPAP is really for someone who needs support with ventilation with volume of ventilation so it helps you get air in with a higher inhalation pressure which reduces Airway resistance with help you get larger volumes to facilitate gas exchange and a veal are recruitment in some instances and then also has a reduced usually lower expiratory pressure to help get that air out but still provide peep. BiPAP is usually used on those that require help compensating for metabolic acidosis or to help reduce hypercarbia in those that have respiratory acidosis.

Has 1 years experience.

Hi Gang,

I am a Respiratory Therapist and I think I can clear the Pressure Support (PS) mystery up a bit. PS was originally created to over come the work of the dead space in the vent circuit. Dead space is non-gas exchange areas in the ventilator structure. Adding a 6 foot corrugated tube that carries air to the patient adds to the work of breathing. PS helps to decrease this work by decreasing the amount of dead space. It's like a proverbial step stool. Cpap and Bipap supply pressure that still exists when the patient exhales. This positive end expiratory pressure (peep) holds the alveoli open therefore increasing O2 in the blood. This is a simplified version but I think you can get the point!


Our one-year-old has been on a vent 24/7 since birth, so we're always learning and exploring the wonderful world of ventilation modes. She started on pressure control and is now on pressure support. She also tried NAVA when she was intubated, but didn't tolerate it well. We are gradually lowering the pressure support in hopes of getting her to CPAP, then off of the vent completely. She has a trach, so all of these modes have been used invasively on her. I must say that when it comes to ventilators, the Astral 150 is an amazing piece of technology, and has been great for home use and travel.