Author: Tucker Matthews
Back with another dive into some airway literature. Got a few studies looking at prehospital airway management of out-of-hospital cardiac arrest, which seems to be a pretty popular area of publication these days. Then have a study looking at tube confirmation with ultrasound, so we don’t have to just cross our fingers and pray while watching the pulse ox.
Paper 1: Benoit JL, Lakshmanan S, Farmer SJ, Sun Q, Jordan Gray J, Sams W, Tadesse DG, McMullan JT. Ventilation Rates Measured by Capnography during Out-of-Hospital Cardiac Arrest Resuscitations and their Association with Return of Spontaneous Circulation. Resuscitation. 2022 Dec 5:S0300-9572(22)00734-1. doi: 10.1016/j.resuscitation.2022.11.028. Epub ahead of print. PMID: 36481240.
They tried to investigate ventilation rate during CPR during out of hospital cardiac arrest by conducting a retrospective observational cohort study over two years, using continuous waveform capnography to calculate ventilatory rates.
Results:
-Primary outcome was ROSC, with secondary outcomes of vital status on arrival to the hospital, and survival to hospital admission.
-Total cohort size of 314 cases.
-Should also note that these cases were non-traumatic.
-Pretty interesting that only 22% of patients received a guideline-compliant ventilation rate of 8-10 breaths per minute.
-20% achieved ROSC prehospital, with 23% surviving to hospital admission.
-Using multiple models to attempt to control for the fact that we don’t actually know the optimal ventilation parameters for OHCA, they actually didn’t find any statistically significant associations between ventilation parameters and patient outcomes.
Thoughts:
These are only initial outcomes, so that’s a limitation for sure. I also always struggle with these OHCA papers because I’m not really sure how useful it is to group all of these cases together. There’s just so much variability depending on the cause of arrest. For example, hypercapnic patients might be particularly susceptible to inadequate ventilation rates. And there is likely further detail depending on each actual pathology. So it will require really large sample sizes to see these differences, and super smart researches to know how to look for them. This is especially true given how poor the outcomes are in these patients at baseline.
I actually like their methods though, and thought it was overall really well written and presented. And it’s pretty interesting that there aren’t differences based on ventilation rate, and if anything is reassuring that we might not have to be so focused on that part of our CPR care. Not to say that it doesn’t matter, but that it doesn’t matter so much that it shows up here. That being said, we have published guidelines, and it’s a bit concerning how poor the compliance was with the recommendation of 8-10 breaths per minute.
Unfortunately, they only had usable capnography data on less than half of their sample size, which is probably to be expected, but it’s possible that those patients in whom the data was unusable weren’t a random collection of patients.
Overall: There is no obvious association between ventilation rate during OHCA and initial patient outcomes. It’s probably best to stick with the 8-10 breaths per minute guidelines for now, but there’s not exactly robust evidence to prove that.
Paper 2: Risse J, Fischer M, Meggiolaro KM, Fariq-Spiegel K, Pabst D, Manegold R, Kill C, Fistera D. Effect of video laryngoscopy for non-trauma out-of-hospital cardiac arrest on clinical outcome: A registry-based analysis. Resuscitation. 2023 Jan 5:109688. doi: 10.1016/j.resuscitation.2023.109688. Epub ahead of print. PMID: 36621529.
Retrospective study out of Germany investigating video laryngoscopy (VL) versus direct laryngoscopy (DL), using patient-centric cerebral performance categories on discharge as a primary outcome.
It’s actually kind of unclear if VL leads to better outcomes. It does seem like VL most likely increases first pass success rates, but this also isn’t totally clear, given that first pass success is such an ambiguous and inconsistently defined term. It’s also unclear if improved first pass success actually leads to any improved patient-centered outcomes. So it’s admirable that they are trying to directly evaluate for VL’s effect on something like neurologic outcomes.
That being said, this is a retrospective study, which isn’t ideal.
Logistically, Germany has physicians on the ambulances that respond to high acuity things like OHCAs, and are typically the person who performs the intubation, if indicated.
They looked at a total of 14,387 patients, 2201 of whom were in the VL group, and 12,186 in the DL group. That’s already initially interesting to me, as VL is kind of complicated in pre-hospital settings, and they don’t really go into whether it’s typical for VL to only be used in the actual ambulance, or if they routinely bring a VL setup to the patient while they’re lying on the ground in arrest. Overall it just seems that there’s probably some bias here that explains why these patients were the ones to get VL.
And this is unfortunately backed up by the data. The VL patients were just overall different. Patients who ultimately received VL had more use of mechanical resuscitation devices, intraosseous lines, which suggests that there may be certain groups who were preferentially using VL, Lucas devices, and IOs.
In regards to the outcomes themselves, there were some kind of odd results. There was a significantly increased rate of multiple ETI attempts with VL, and more of them arrived to the hospital with ongoing CPR, but they also wound up with improved survivals to hospital discharge and discharge with favorable neurologic outcome. The authors postulate that this is because of improved early oxygenation, but there’s not really data to support this in their paper, since the time from EMS arrival to ETT placement wasn’t different between the groups, nor was the time until hospital arrival.
But why would they have increased attempts and improved outcomes? Maybe the increased attempts is because it’s used as a rescue device, and then the improved outcomes are from some separate factor, but it’ s just not clear.
Because of that I’m just not convinced that the use of VL itself matters, but that maybe it’s just a confounder that we’re not seeing because of the retrospective nature of the study. If anything, this study maybe just indicates that providers using VL in the prehospital setting are doing something that might improve overall patient-centered outcomes. But maybe that’s just because they’re more up to snuff on recent resuscitation techniques.
Paper 3: Lou J, Tian S, Kang X, Lian H, Liu H, Zhang W, Peran D, Zhang J. Airway management in out-of-hospital cardiac arrest: A systematic review and network meta-analysis. Am J Emerg Med. 2022 Dec 29;65:130-138. doi: 10.1016/j.ajem.2022.12.029. Epub ahead of print. PMID: 36630861.
This is a systematic review and meta analysis looking at airway management during OHCA, using primary outcome of survival to discharge. Most surprising to me is that this only was able to identify 9 RCTs between 1986 and 2018. It’s also surprising that it took them five years to publish this.
I’m always curious of how the debate between LMA and ETT will proceed now that iGels are so easy and widespread, but portable and easily useable VL is also spreading. So I always like studies like this.
I’m not super convinced that their statistical methods would really allow them to just compare data between these different studies as they do, but I’m certainly no statistics expert, so ok I guess. But different studies used different types of providers for the management (EMT versus physician versus paramedic), so I’m not sure that this is a valid method of comparison.
Overall, they interpret the data as suggesting a superiority of laryngeal mask or esophageal tracheal combitube, with bag valve mask ventilation as the worst. In between were i-gel, endotracheal intubation, and a laryngeal tube (in that order from best to worst). But the confidence intervals were enormous.
I’m not sure I really care that much about their other measured outcomes, since they aren’t really patient-centered, and I’m not sure how comparable they are between different methods. Like, what does airway technique success rate mean for bag mask ventilation?
So all in all I guess that these data don’t show me anything particularly shocking or convincing, but they do seem consistent with what I think most people would logically think. Basically, supraglottic airways are really great and fast, and probably provide enough airway security that there’s not much of a reason to intubate, especially given the time and skills needed for that. And then obviously, we shouldn’t just be bagging these patients throughout transfer prehospital. But at the end of the day, this is only nine studies…
Paper 4: Roy PS, Joshi N, Garg M, Meena R, Bhati S. Comparison of ultrasonography, clinical method and capnography for detecting correct endotracheal tube placement- A prospective, observational study. Indian J Anaesth. 2022 Dec;66(12):826-831. doi: 10.4103/ija.ija_240_22. Epub 2022 Dec 20. PMID: 36654895; PMCID: PMC9842085.
This is a really interesting study. This is out of India, attempting to determine the test characteristics of using ultrasound for endotracheal tube placement confirmation versus that of “clinical method” (chest rise and auscultation). In particular, they wanted to evaluate patients with higher ASA grades—who have not typically been included in similar studies—and to also include time until detection as a dependent variable. They used a prospective, observational study of ICU patients, and chose waveform capnography as a gold standard.
The specifics of their methods are kind of awesome. They had three different designated anesthesiologists perform the three different confirmation methods simultaneously, and then measured the times.
It’s not a huge study—92 patients—but it’s still decent, and the data seem pretty clear. It is a bit weird that the mean age was 37, since that seems really young, but probably doesn’t significantly impact the study findings.
It’s really odd to me that they don’t specify anything about the intubations themselves. So we don’t know if these are direct versus video laryngoscopy. That feels important since there were 7 esophageal intubations, which is terrifyingly high. They also didn’t show the data for the actual difficulty of the intubations themselves. I don’t care so much about airway confirmation in cases where the tube is easily visualized passing through the cords.
The important thing though, is that ultrasound performed phenomenally, with no false positives or negatives, while the clinical method had really bad specificity and NPV values (28.6% and 40%, respectively). That pretty clearly shows how useless it is to use chest rise with auscultation.
What’s also really interesting to me was how fast ultrasound was to confirm. It only took 4.9 seconds on average, while capnography took 15.4 seconds. Not that it really matters, but the clinical method took 17.8 seconds; just more reason not to use it.
For me, I find myself not using ultrasound, mostly due to the fact that the machines are massive, and get in the way of a crowded room during intubation. That being said, if I worked somewhere with larger resus rooms, or if I had access to smaller ultrasound machines, I would be really tempted to start ultrasounding these more, given how bad it can be to accidentally not realize that you intubated the esophagus.