Non-invasive Ventilation in Acute Pulmonary Edema
Today’s simulation led to a discussion of the optimal therapy for treatment of the acutely dyspneic, diaphoretic, tachycardic, hypertensive distressed patient with acute pulmonary edema. After discussing the routine medical therapies — nitro SL, nitro gtt, ACE inhibitors, and furosemide — the discussion turned to the role of non-invasive ventilation (NIV).
It is no longer thought to be controversial that a trial of NIV is a crucial intervention for patients presenting with acute pulmonary edema prior to committing to endotracheal intubation (assuming that the patient has the mental status to tolerate NIV). The controversy lies in which modality of NIV to use — continuous positive airway pressure (CPAP) vs. bilevel non-invasive positive pressure ventilation (NIPPV), commonly referred to by the proprietary name BiPAP®.
Theoretically, it seems that BiPAP would be superior to CPAP since in addition to the basal positive pressure of CPAP which helps to stent open alveoli prone to collapse due to the weighty edema filling the lungs, there is an augmentation with positive pressure during inhalation to reduce the work of breathing. It would seem to follow that BiPAP would likely be superior to CPAP in reducing rates of intubation and possibly even mortality, while both modalities would be superior to just oxygen alone as they prevent derecruitment of alveoli.
Numerous trials have studied whether NIV is superior to oxygen alone when used to augment medical therapy for APE. Recent meta-analyses in JAMA (PMID: 16380593) and Critical Care (PMID: 16646987 and 16569254) have concluded that both CPAP and BiPAP are effective in the treatment of acute pulmonary edema with respect to the endpoints of mortality and subsequent need for intubation. However, all three meta-analyses find that BiPAP is not superior to CPAP with respect to either of these two endpoints.
All three articles make mention of a 1997 comparison study of BiPAP and CPAP by Mehta, et al. published in Critical Care Medicine (PMID: 9142026) which was terminated after interim analysis indicated that the patients randomized to the BiPAP arm of the study suffered greater myocardial infarction rates than those receiving CPAP (71% vs 31%). The articles mention that subsequent studies have failed to show this disparity and that the numbers in this trial we very small. Despite these assurances, none of the authors’ conclusions recommend a strategy of BiPAP over CPAP in lieu of the fact that the “physiological benefits [of BiPAP] did not translate into primary outcomes.” (JAMA). The JAMA article goes on to conclude that
the question of whether one technique offers advantage over the other and what subset of patients would benefit more with either one of these techniques remains unresolved.
The first of the Critical Care articles concludes that CPAP should be the NIV of choice because “from a practical point of view CPAP has been shown to be cheaper and easier to use” while the second recommends whichever modality is available.
ACEP also weighed in on this controversy in early 2007 when it published its Clinical Policy on patients presenting to the ED with acute heart failure syndromes. ACEP recommends the use of CPAP as a level B recommendation and downgrades the use of BiPAP to a level C recommendation citing the possible increase in myocardial infarction in conjunction with the lack of observed benefit over CPAP in the two main endpoints, mortality and reduction in the need for intubation.
Bottom line: It’s the smart and safe move to favor CPAP over BiPAP unless and until BiPAP is shown unequivocally to be more effective than CPAP with similar safety profile.
Posted
on Thursday, August 23rd, 2007 at 3:27 am by Sohan. Filed under
CHF, Ventilation, ACS.
You may post a comment.
nice entry sohansolo.. i once had an old guy patient who got ape after getting really agitated over his broken bed in the middle of the night. I’m not sure what broke his bed but the bipap we used on him worked wonders. also, that pic of me gives me nightmares.
Comment by bing on August 23rd, 2007 at 6:25 am
Sorry about this picture b-shen; if you want to change it, we can. Anything else you want up there about yourself?
Comment by Sohan on August 23rd, 2007 at 12:45 pm
Sohan,
That picture of Bing also gives me nightmares…
Vacation stole me away from conference - was there discussion re: IV ace for ape.
Comment by phil on August 24th, 2007 at 4:40 pm
Phil,
We touched on enalaprilat but didn’t dwell on it except to note that some people have used it although most tend to avoid ACE inhibitors due to concern for hypotension. No evidence based discussion was had. Sorry we missed you at conference.
Comment by Sohan on August 26th, 2007 at 12:14 pm
hey buddy,
i’m writing only to you in response to your blog entry, feel free to post it whereever you feel appropriate.
This entire topic has been muddled by researchers who are not careful or precise with their terminology. There is seemingly this concept in people’s heads that BiPAP and CPAP are entirely different things. The big question is whether non-invasive ventilation (NIV) is good in APE; as you eloquently summarized, the answer is–yes, it is good. Then the second question is what settings should you put the patient on? BiPAP and CPAP are not different therapies, they are just different settings on whatever NIV machine you are using.
What we know about decompensated CHF patients is that they need PEEP. PEEP is the cure for every aspect of the disease process. They do not have any reason to be hypercapneic and their lung parenchyma is usually intact. Their problem is too much fluid in the lungs, due to too much afterload and occasionally fluid overload resulting in excessive preload. PEEP solves all of these problems. PEEP alone is CPAP. There is absolutley no physiological or theoretical reason that adding pressure support to PEEP (at which point the mode is called BiPAP or bilevel NIV or the confusing term you used in your post, NIPPV) Pressure support does not cause additional recruitment nor does it benefit the underlying physiology of a CHFer. It is not at all suprising that there has been no proven additional benefit to BiPAP over CPAP.
That being said, nor has there been any evidence of risk. The Mehta study you mention was not a study of BiPAP vs. CPAP. It was a study of an adequate dose of CPAP vs. a wholly inadequate PEEP setting, an unnecessarily high PS setting, and a mandatory back-up breath rate. It is the latter that probably wound up killing these patients’ hearts. In the CPAP patients, there was enough PEEP for them to get better or else they showed they were not making it and could get intubated because there were no mandatory breaths. So you can see what the patient was doing on their own. In the BiPAP group, the machine would still give breaths even if the patient tired. Since these patients were not getting the treatment they needed in the first place, it is not hard to see how this can lead to MIs.
Rarely is any PS needed, but as long as the dose of PEEP is adequate, there is no harm adding some pressure support. That being said, when I have a CHFer that can not manage their ventilatory requirements, I intubate, I don’t add PS.
You should start these folks off at a PEEP of 8-10 and you can go up to 15-18 as long as their pressure handles it. The esophageal sphincter probably starts popping open around 18, so I don’t go beyond that. If you add PS to the mix, ti actually limits how high you can go on your peep.
take home:
-no reason to think BiPAP should be better than CPAP
-BiPAP not shown to be better in studies.
-No reason to think it will harm patients if you set the PEEP to what the patient needs
-If patient too drowsy to trigger NIV, intubate them, don’t put them on mandatory rates
-BiPAP and CPAP are not disparate things, they are just settings in the same ventilatory mode
Comment by scott on September 24th, 2007 at 11:43 am