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)
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)
- Kacmarek, Robert M., James K. Stoller, Albert J. Heuer, “Egan’s Fundamentals of Respiratory Care,” 10th edition, 2013, Elsevier Mosby, pages 1066, 1134-5
- “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
- Criner, Gerard J., Rodger E. Barnette, Gilbert E. D’Alonzo, editors, “Critical Care Study Guide: Text and Review,” 2nd edition, 2010, Springer
- 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
- Maclntyre, Neil R., “Mechanical Ventilation: Noninvasive Strategies in the Acute Care Setting,” Medscape, http://www.medscape.org/viewarticle/450209, accessed 3/31/17
- 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
- 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
- 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