Tuesday, September 24, 2019

High Flow Nasal Cannula in Acute Decompensated Heart Failure data leaves much to be desired.

Fortunately in the critical ill population, we do not necessarily have to abide by the saying that "if all you have is a hammer, everything looks like a nail". What I'm referring to is regarding utilizing high-flow nasal cannula in acute heart failure exacerbations. I already dissected how HFNC generated a "PEEP" equivalent airway pressure and the data behind that statement. The amount of PEEP varies and it drops by a statistically significant difference if the patient has their mouth open. If a patient presents to the emergency department, or someone gets overzealous with maintenance fluids, with an acute heart failure exacerbation, there is data that I will be reviewing here where HFNC is an option. But let's be honest with ourselves, though, non-invasive ventilation (colloquially known as BiPAP, although CPAP has data for working as well) is the better option because it provides positive airway pressure more reliably that HFNC. Sometimes these patients just need the ventilator as well. All three studies are FREE that I am going to be reviewing here and I recommend you read them for yourself rather than trusting my takedown of them. That's your disclaimer.

The first study published in 2011 out of Spain was a look at just 5 patients. I know, don't fall off of your seat. I can't criticize because I don't do any research outside of read other peoples research. One needs to remember that in 2011 the HFNC systems were not readily available for historical context. These 5 patients were treated in the emergency department with NIV and then I guess they were diuresed aggressively there. Why do I guess? Well the study does not report the BNP nor the achieved diuresis in these 5 patients. Big weakness in the study. They looked at a multitude of parameters that would be standard for a study of this nature, i.e. to see if HFNC is better than the other oxygen devices, but there are big problems. You see, the authors looked at the parameters before HFNC and then 24 hours AFTER HFNC. What they don't say is how much the patients were diuresed in the interim. Of course the PaO2 is going to improve. Of course the dyspnea is going to improve. Of course the respiratory rate is going to improve! Anyway, this is a study worth sticking in our back pockets to know it happened and move forward.

The second study by Roca also out of Spain in 2013 wanted to assess if HFNC helped with the hemodynamic parameters. They hypothesized that HFNC in patients with heart failure could be associated with a decrease in preload without changing the cardiac output. To look at this, patients got sequential echo's to assess cardiac function. Pretty good setup if you ask me. The 10 patients enrolled in this study were all stable. Therefore the data needs to be extrapolated to the sick patients. They did a baseline TTE on these patients, then hooked them up to the HFNC system at 20L, checked an echo, then at 40L of flow, and checked an echo. They did all sort of echocardiographic wizardry to obtain their results. They found that HFNC may be associated with a decrease in preload justified by the lack of IVC collapse on inspiration without any changes to cardiac function. IVC measurements are their own can of worms when used for resuscitation but this is very standardized and methodical. The most interesting finding that I enjoyed was the decrease in respiratory rate noted by these patients. At baseline, their RR was 23 breaths per minute. At 20L this fell to 17 bpm. At 40L this fell to 13 bpm. Cool stuff! Note that the patients were receiving just flow in this study as the FiO2 was set to 21% (room air). The authors chose to not use patients in acute decompensated heart failure for this study as there would have been too much variability in the subjects themselves along with their responses to the treatments interfering with to the measures. Obviously if they dump out a liter due to furosemide their hemodynamic parameters are going to change and it'll mask out the effect of the HFNC or provide confounders.

The third and last study I'm going to share with you all today comes from our colleagues in South Korea who performed a retrospective cohort analysis where patients were divided into a HFNC group or an intubation group after oxygenation with a facemask at a flow rate of 10L/min or more. These authors jumped on the opportunity to look at this data as they hadn't seen any published data about using HFNC in patients with acute heart failure exacerbations. They looked at approximately 5 years of data to place 73 patients in the intubation group and 76 patients in the HFNC group. Since this was a retrospective study, the decision as to what arm the patients fell in was at the discretion of the physician at bedside. The authors are just looking back in time at why they decided to do it and how the patients did. It seems as if they ignored the NIV data. I could be wrong. The baseline characteristics of the two arms were similar with nothing too eye catching. These patients were looked at for 6 hours. There were no statistically significant changes in the physiologic responses between the two groups. There was also no difference in the clinical outcomes between the two groups. This oddly, in my opinion, includes vasopressor/ionotrope use. I mention this because patients who are intubated typically have sedation. Also, the medications utilized for intubation could have an effect on hemodynamic parameters that are not noted here. It's just something that, from a personal experience standpoint, has me a bit curious. The p-value for that is 0.051. If the sample size would've been larger, I'm sure that would've been a notable difference. The authors noted all these limitations to their study and agree that what we really need is a prospective, multicentered, randomized, controlled trial. I agree

To conclude, I think the best we have right now in the absence of concrete data is clinical judgment, my favorite. One could try to place the patient on HFNC to either keep them away from the ventilator or even keep them from being annoyed by the CPAP/BiPAP mask which is typically uncomfortable, limits the ability to eat, speak, and other fun activities. If it fails, it fails. Your RT may be a little annoyed at you and may say "I told you so", but ultimately we have to do what's best for the patient. Thoughts? Please read these articles for yourself. A hat tip to all the authors. 

- EJ

Link to Abstract

Link to Full FREE PDF

Link to Abstract

Link to not free PDF

Link to Abstract

Link to Full FREE PDF
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