BiPAP and CPAP: Answering all your questions

Your question: How high can you set CPAP? What are the disadvantages of CPAP that is too high?

My answer. This is a good question. According to Egans, CPAP is a continuous flow of pressure on inspiration and expiration.If there are alveoli that are collapsed due to atelectasis, CPAP acts to recruit them, and open them up. It thereby acts as a splint to keep them open to improve oxygenation. If CPAP levels are set too high, alveoli will be over-distended, and this may result in air trapping. (1, page 1066)

Another thing to keep in mind here is that CPAP acts to reduce venous return to the heart so the heart doesn't have to work so hard to pump blood through the body. This is the advantage of using CPAP to treat heart failure. If CPAP is set too high, this pressure may ultimately reduce venous return enough as to cause a reduction in cardiac output, which can be measured by a drop in blood pressure.

Over-distended alveoli and air trapping can also result in a drop in oxygen levels, and this can be measured by oxygen saturation monitor.

Your Question. How high can you set IPAP on a BiPAP machine?

My answer. The best answer I can give to this question is a theory, as is much of the medical profession. From what I have read (and you can help me find a source here) is that a pressure support or IPAP higher than 20 in a non-intubated patient may act to obstruct, or block, the esophagus. This can prevent the patient from swallowing. You can exceed a pressure of 20 if you absolutely must to improve oxygenation or ventilation. However, if you must do this, talk to the doctor about ordering a nasal gastric tube (NG). 

While it's generally not a good idea to exceed the recommended settings, I have from time to time had doctors insist I do this. I just make sure to remind the physician that there is a down side to too much pressure.

Your question.  Is it true that you need an IPAP greater than 10 to be therapeutic?

My answer. The goal of IPAP is to assist with inhalation to reduce work of breathing and improve ventilation. If an IPAP of 10 results in an ideal tidal volume for that patient, then an IPAP of 10 will be fine. Some patients have small frames, in which case an IPAP of 10 (or less) may provide adequate support. Keep in mind here that some people with COPD do not have enough lung function, especially during flare-ups, to adequately blow off CO2. For these patients, just assisting them get to their normal, ideal tidal volumes will be all that is needed. So, you do not necessarily have to blast patients with the highest pressure support. If you are getting adequate tidal volumes (using your usual formula of 6- ml/kg ideal body weight), then you are probably fine.

Your question. Is it true you can't set a rate on BiPAP?

My answer. Part of the advantage of BiPAP, is if the machines senses that a patient hasn't taken a breath, it can force the patient to take a breath. This is ideal for preventing sleep apnea. So, ideally, you should set the BiPAP rate at around 6-8. Usually patients will breathe over this set rate. However, if they don't, then the machine will assure at least a minimum respiratory rate.

Your question. How are CPAP and BiPAP set? What are the ideal settings to use?

My answer. The ideal settings should be determined by doing a sleep study. A sleep study technician will titrate settings until the best settings are determined. You will want the lowest setting necessary to keep airways open and maintain adequate oxygenation. Of course, you don't want too high to prevent drops in blood pressure and oxygenation as noted above. There are also newer machines that are auto-titrating.

Your question. When you are setting up a patient on BiPAP in the clinical setting, what are good start settings?

My answer. This is open to debate. It is also open to varying opinions. The general consensus where I work is ideal start-up settings are IPAP 10 and EPAP 4. Settings can be adjusted until an ideal tital volume and oxygenation status is determined.

Your question. How big of a gap between IPAP and EPAP do you need.

My answer. The answer here is another one that is open to personal opinion. The general consensus where I work is that you would like to keep the gap at a minimum of 5. For example, you will want to set the IPAP at least 5 over EPAP. Keep in mind, however, the ventilator that you are using.

Your question. How is Pressure Support (PS) measured on BiPAP. It depends on the machine you are using. On the V60, it is measured over PEEP. So, if you are using a V60 ventilator, and you have the IPAP set at 10 and the EPAP set at 5, you are essentially using a Pressure Support of 10 and a CPAP of 5. On the other hand, if you are using a machine that does not measure PS over PEEP, and you use settings of 10/4, then the measured PS is 5. So, this is why it's important to know your machine.

Your question. Is it true that if a patient requires BiPAP post extubation that the patient never should have been extubated and should be re-intubated?

My answer. Actually, this subject has been extensively studied, and the results are relatively inconclusive. However, some studies show that BiPAP post extubation may prove useful in some patients, especially those with end stage COPD where airway protection and pulmonary toilet is not a concern. This may occur when patients are incorrectly assessed for readiness to wean, or when patients self extubate. It may also occur in some patients, such as those with end stage COPD who are anticipated to still need some support although you don't want to risk further complications of intubation, and a trial of post-extubation BiPAP is done on purpose. Some studies do show this may prove beneficial. However, it should also be noted that the patients described here have a 40% mortality rate.  (5)

Your Question. Does BiPAP really help with heart failure? Doctors say it pushes fluid out of the lungs.

My answer. Both CPAP and BiPAP, by providing increased intrathoracic pressure, have been shown to reduce both cardiac preload and afterload, which reduces the amount of work the heart has to do. Some physicians think it works by pushing fluid out of interstitial spaces, and this is why it works. However, while this does occur to a small extent, it's not enough to have a therapeutic benefit. (5)


Your Question. Does BiPAP truly benefit people with COPD.

My answer. Yes. Studies seem to show that IPAP reduces airway resistance due to bronchospasm and secretions to make it easier to take in a breath and reduce dyspnea The machines can also sense when a patient has not taken a breath to force them to take a breath, thereby preventing apnea. EPAP also acts to splint the upper and lower airways to keep them open at end expiration. This prevents soft tissues in the upper airway from collapsing and causing apnea, and it also recruits collapsed alveoli and keeps them open to improve oxygenation. Various studies have shown that BiPAP used to treat episodes of severe COPD, whether caused by COPD or heart failure, in the hospital setting greatly improves outcomes and hospital length of stays, and reduced hospital costs. Part of this is because BiPAP often prevents the need for invasive intubation and mechanical ventilation. Nocturnal BiPAP used every day at home for a minimum of four hours per day significantly reduces COPD flare-ups and makes them less-severe when they do occur. This has made it so that people living with COPD can live long lives with quality. (1, 4, 6)

References:

1. Kacmarek, Robert M., James K. Stoller, Albert J. Heuer, “Egan’s Fundamentals of Respiratory Care,” 10th edition, 2013, Elsevier Mosby, pages 1066, 1134-5
2. “Non-Invasive Ventilation in COPD Exacerbations,” Nursing Times, September 3, 2013, https://www.nursingtimes.net/clinical-archive/respiratory/non-invasive-ventilation-in-copd-exacerbations/5062992.article
3. Criner, Gerard J., Rodger E. Barnette, Gilbert E. D’Alonzo, editors, “Critical Care Study Guide: Text and Review,” 2nd edition, 2010, Springer
4. Respiratory Therapy Magazine: Noninvasive BiPAP Systems May Help COPD Patients, January 28, 2015, http://www.rtmagazine.com/2015/01/noninvasive-bipap-systems-may-help-copd-patients/, accessed 3/31/17
5. Maclntyre, Neil R., “Mechanical Ventilation: Noninvasive Strategies in the Acute Care Setting,” Medscape, http://www.medscape.org/viewarticle/450209, accessed 3/31/17
6. Ankjærgaard, Kasper Linde , et al., "Home Non Invasive Ventilation (NIV) treatment for COPD patients with a history of NIV-treated exacerbation a randomized, controlled, multi-center study," BMC Pulmonary Medicine, 2016, http://bmcpulmmed.biomedcentral.com/articles/10.1186/s12890-016-0184-6, accessed 4/1/17
7. Respiratory Therapy Magazine: Nocturnal BiLevel Ventilation for the COPD patient," February 7, 2007 http://www.rtmagazine.com/2007/02/nocturnal-bilevel-ventilation-for-the-copd-patient/, accessed 4/1/17
8. Lainscak, Mitja, Stefan D. Anker, "Heart failure, chronic obstructive pulmonary disease, and asthma: numbers, facts, and challenges," ESC Heart Failure, volume 2, issue 3, 2015, pages 103-107, http://onlinelibrary.wiley.com/doi/10.1002/ehf2.12055/pdf, accessed 4/2/17

CPAP -vs- BiPAP: What RTs Need to Know

Non-invasive positive pressure ventilation (NIPPV) include machines that allow you to ventilate and oxygenate patients without the need to perform the invasive procedure of intubation. These machines can only be used on a spontaneously breathing patient.

Another acronym commonly used to describe NIPPV is NIV, which essentially stands for Non-Invasive Ventilation. You may actually see other similar acronyms, and they all essentially refer to the same thing.

The two most common forms of NIV are:

1. CPAP 
2. BiPAP 

So, what are they and how might they help your patients?

1. CPAP: This is continuous positive airway pressure. It's a pressure exhale applied during the respiratory cycle that helps keep air passages open so that the next breath comes in easier. Since it keeps the airways patent, it assures adequate oxygenation, and is often prescribed to increase oxygenation.

Indications for CPAP.

• Hypoxemia that is refractory to high concentrations of oxygen by other means. 
• Obstructive Sleep Apnea to prevent the upper airway from collapsing 

Adjusting CPAP settings. CPAP is increased or decreased to maintain a desired SpO2, which is usually greater than 90% SpO2 and 60 PaO2.

BiPAP: This is an acronym for Bi-level (or Biphasic) Positive Airway Pressure. It provides a combination of both IPAP and EPAP.

• IPAP. This is Inspiratory Positive Airway Pressure. It is a pressure during inspiration that assists a patient obtain an adequate tidal volume. Because it provides assistance with inhalation, it therefore decreases the work of breathing required to get air in. Because it assures adequate ventilation, it is often prescribed to blow off carbon dioxide (CO2). 
• EPAP. This is Expiratory Positive Airway Pressure. It is the same thing as CPAP. EPAP is simply used here so you know your talking about CPAP on a BiPAP machine. EPAP is used to improve oxygenation.

Indications for BiPAP.

• Respiratory Failure due to accessory muscles fatigue. It assures adequate ventilation to blow off CO2 and improve oxygenation. 
• COPD to decrease airway resistance, thereby decreasing work of breathing required to take in an adequate tidal volume. By increasing ventilations, it helps to blow off CO2. It also keeps airways patent to improve oxygenation. 
• Pulmonary Edema to help decrease cardiac output which decreases venous return to the right ventricle to reduce blood return to the heart. It also keeps airways patent to help improve oxygenation. It also helps keep alveoli patent to improve oxygenation (prevents alveolar collapse). By keeping alveoli patent, and redistributing alveolar fluid, it helps to reduce pulmonary compliance and reduce work of breathing. 
• Atelectasis to help keep airways patent to improve oxygenation 
• Pulmonary Embolis to improve oxygenation 
• Pneumonia to assure adequate ventilations and oxygenation

Adjusting BiPAP settings. As a rule of thumb, the following rules are true.

IPAP. Increase to blow off CO2. It should not be higher than 20 to prevent pressure from blocking the esophagus. By providing adequate tidal volumes it may also help improve oxygenation.

EPAP. Increase to improve oxygenation.

PS. Pressure Support. This is the gap between IPAP and EPAP. The greater the PS is the more CO2 will be blown off.

Patient Leak. It is important to have a small leak to prevent skin breakdown. Most modern machines will compensate for a small leak.

Alarms. Adjusted as appropriate for each patient.

Contraindications for BiPAP include.

• Inability of patient to protect own airway (decreased level of consciousness). This includes the inability of the patient to pull off the mask if it becomes full of fluid, such as vomit or spit. 
• Increased secretions (i.e. pulmonary edema, increased sputum production) 
• Any patient at risk of vomiting (post stomach surgery, drug overdose). In this case you may be able to use BiPAP if an NG is inserted. Most machines will compensate just fine for the leak around the tube. 
• Bullous lung disease (emphysema) because the high pressure may cause a pneumothorax 
• Pneumothorax may be complication due to increased pressure;;may blow out rest of good lung 
• Hypotension; High pressures decrease cardiac output 
• Non-compliant patient. Surely you cannot force a patient to use this equipment. 

Study Results. Studies show that the use of NIPPV for respiratory failure in COPD patients results in a greater reduction in CO2 and a normalization of pH, compared to those in the control group who did not use NIPPV. A study also showed those receiving conventional therapy were intubated 67% of the time, while those receiving NIPPV were intubated only 9% of the time. This prevents the complications of mechanical ventilation, particularly the difficulty associated with extubating patients with lung disease.

Studies also show that length of stay in a hospital is reduced among the COPD pupulation using NIPPV. NIPPV may also be used on the medical/ surgical floors, reducing cost. However, those in severe respiratory failure may still require a stay in the critical care unit.

Studies also show that most patients, or about 80%, tolerate NIPPV just fine. (see references #3 and 4 below).

Bottom Line. Non-Invasive Positive Pressure Ventilation machines are ideal for many patients to improve oxygenation and ventilation. They have prevented many critical patients from having to go through the invasive procedure of intubation and mechanical ventilation. They are also useful to assure adequate ventilation and oxygenation in the home setting, especially during the nighttime when breathing seems to be more relaxed.

This post was originally published on 8/4/8 on respiratorytherapycave.blogspot.com; it has been edited for accuracy.

Further Reading.

• Good start settings for BiPAP
• My interview with Roxlyn Cole, A COPD patient who uses BiPAP at night
• Study: Non-Invasive Positive Pressure Ventilation For Acute Respiratory Failure
• Barnes, Peter J., et al, editor, "Asthma and COPD: Basic Mechanisms and Clinical Management," 2nd edition, 2009, page 842 
• Non-Invasive Positive Pressure Ventilation (CPAP or BiPAP NPPV) for Cardiogenic Pulmonary Edema
• 17 Biggest Myths of Respiratory Therapy