Papers of February

Here is a overview of the papers that caught our eye this month and the accompanying podcast. As always make sure you go and check out the papers yourself as this is just a whistle stop tour to wet your appetite……

Chest wall thickness and decompression failure: A systematic review and meta-analysis comparing anatomic locations in needle thoracostomy. Laan DV1. Injury. 2015 Dec 13. pii: S0020-1383(15)00768-8. doi: 10.1016/j.injury.2015.11.045. [Epub ahead of print]

So needle compressions (or needle thoracostomies/NT), certainly in the UK, tend to be performed when the clinical diagnosis of a tension pneumothorax has been made.  The initial decompression of some of the pneumothorax in the peri arrest patient is done to give clinicians a small bit of added time to place a definitive chest drain. This tends to be done with a 14 gauge cannuala in the 2nd intercostal space (ICS) in the mid clavicular line. The cannula has a length of approximately 5cm.

Is the 2nd ICS the best location to place this potentially life saving catheter and to answer this we need to think about the thickness of the chest wall in different locations. This paper is a was a systematic review trying to answer the chest wall question.

In the review they included a range of studies from cadaver, some random CT samples and others trauma cohorts requiring NT. They assessed the thickness of the chest wall and associated success of NT with a chest wall thickness of less than 5cm.

They compared the mean failure rate of the 3 following locations; 2nd ICS MCL, 4th or 5th ICS-MAL (mid axiillary line) and 4th or 5th ICS-AAL (anterior axillary line) and found respective mean failure rates of 38%, 31% and 13%.

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Weaknesses; doesn’t take into account the difference in chest wall thickness that occurs when placing pressure on the chest whilst performing NT, it doesn’t take into account the variation in chest thickness when the patient moves from a flat CT scanner to a semi erect position on a resus trolley, technical successes of the placement or kinking of the tube and finally doesn’t take into account complication rates of things such as pneumothoraces when the initial clinical diagnosis was wrong.

Having said that what it tells me is that if you choose to use NT beware that it may fail, you can consider other options rather than just 2nd ICS MCL and that infact the 4th or 5th ICS in the anterior axillary line may be more dependable.

Definitely more work needed than just this paper alone to answer this clinical question but this may open up thoughts of alternative approaches specifically the AAL.

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Efficacy of Nasal Cannula Oxygen as a Preoxygenation Adjunct in Emergency Airway Management. Hayes-Bradley C. Ann Emerg Med. 2015 Dec 31. pii: S0196-0644(15)01500-0. doi: 10.1016/j.annemergmed.2015.11.012. [Epub ahead of print]

Recent DAS guidelines state that in high risk patients supplemental nasal oxygenation should be applied in addition to standard facemask oxygenation. This paper looked to asses the efficacy of supplemental nasal oxygenation in healthy volunteers both with and without an air leak.

The way they quantified the efficiency of pre oxygenation and indeed the primary outcome they looked at, was the end tidal oxygen (ETO2). The 4 pre oxygenation scenarios they simulated were facemask, facemask + nasal cannula, facemask + leak and finally facemask + nasal cannula + leak (NB the leak was simulated via by placing a piece of NG tube between the NG tube and facemask).

Their main findings……

Without a leak ETO2 was similar for a BVM (bag valve mask) with or without nasal cannula but importantly with the presence of a leak the ETO2 was higher with nasal oxygenation present. !s you would expect the presence of a leak reduced the ETO2 lower than both with or without the cannulae.

They also looked at the ETO2 when using a non-rebreather mask and found the ETO2 was increased using a nasal cannualae.

So this is a pretty small study but it does give us a reminder that technique and obtaining a decent seal when pre oxygenating a patient for RSI is really important and it does, in my opinion, add weight to the argument for the use of a nasal cannula in the ED RSI situation regardless of the predicted difficulty of intubation.

More evidence on the topic which you can find more at on our apnoeic O2 podcast.

It’s been shown that you need a 2 person technique for the best seal. This often doesn’t occur pre or in hospital. There may be good cause to add this to the standard practice of those patients even if not deemed high risk.

Utility of gum-elastic bougie for tracheal intubation during chest compressions in a manikin: a randomized crossover trial. Komasawa N. Am J Emerg Med. 2016 Jan;34(1):54-6. doi: 10.1016/j.ajem.2015.09.016. Epub 2015 Sep 21.

Japanese paper, published in the American Journal of Emergency Medicine, lead author Komasawa. As the title suggests this was a study that was pretty small looking at the performance of novice intubators during a simulated cardiac arrest both with and without chest compressions ongoing.

There were was a total of 17 participants, each of whom had completed approximately a month of their anaesthesia induction and head therefore passed approximately 20-30 ET tubes each.

The investigators were looking to compare the ease of intubation both with and without the use of a gum elastic bougie.

They found all candidates were able to successfully intubate the manikin without CPR being performed, however whilst chest compressions were being performed they found a significant difference in the success rate with 16/17 being successful with the use of the bougie versus 10/17 without.

So this is a very small paper, it is a manikin study and can’t necessarily be extrapolated into standard practice in the ED but what it does do is to raise some interesting questions. So in many difficult airway guidelines and algorithms the bougie is there to help once difficulty has been identified during intubation attempts but it does make you question why we wait for the problem to arise before it’s use. If the bougie is going to aid the passage of the tube then surely routine use should be considered?

Some pre hospital services have already moved to this as their first line approach and in an ED which will be preforming some intubations during cardiac arrest when the passage of the tube needs to be successful and multiple attempts by multiple providers may lead to delays and possible interruptions in chest compressions would this not be in our patients best interests?

It’s certainly sparked an interest in the topic for me and something that’s been discussed in our office so we’ll have another podcast looking specifically at this topic in the next couple of months and see if we can get a more conclusive answer to this question.

Influence of EMS-physician presence on survival after out-of-hospital cardiopulmonary resuscitation: systematic review and meta-analysis.Böttiger BW. Crit Care. 2016 Jan 9;20(1):4. doi: 10.1186/s13054-015-1156-6.

Lead author is Bottiger and this is a free open access article and the links to the article will be on the website.

So EMS/prehospital systems vary wildly in their setup and team members, in no small part this is due to the finite resources available to those services but there also needs to a proven benefit to the presence of EMS clinicians when there is a significant financial impact of their staffing.

This paper looked to collate the evidence of the sickest of the sick prehospital patients, those in cardiac arrest. They included observational cohort studies with comparisons between EMS clinician or paramedic led CPR for out of hospital cardiac arrests where survival data was available. Survival to hospital discharge was the primary outcome, although when this wasn’t available they utilised 30 survival or even ROSC.

The authors identified 14 papers with over 120,000 patients incuded to answer their question which had a high degree of heterogeneity. But the headline results;

Pooled estimate for ROSC 36.2% vs 23.4% for clinicians vs paramedics respectively with similarly survival to hospital admission rate of 30.1% vs 19.2% and finally survival to hospital discharge 15.1% for clinicians vs 8.4% for paramedics.

So it appears on multiple fronts that EMS clinician led CPR is associated with improved outcomes from out of hospital cardiac arrests but what it doesn’t answer is what it is about the service and setup that delivers that improved outcome.

There is a huge scope for the result to be clouded by selection bias here with the potential that clinicians are not dispatched to the apparently futile cardiac arrests and therefore get the more likely ‘win’ cases. If clinicians do arrive at futile cases and decide not to start CPR then again the selection bias will falsely show their care to those that they deliver CPR to deliver better outcomes, when infact we are looking at a different cohort of patients with a different prognosis.

The governance regarding EMS providers will also differ with clinicians in some circumstances being able to institute a more advanced life support and maybe this needs to considered when determining the skill set that some services aim to develop/allow more advanced skills to be led by paramedics.

With no RCTs on this topic meta analysing papers with inherent methodological weaknesses won’t lead to a perfect answer but it is the best we have to work with. It does seem to highlight areas that we can look at further though including further analysis on whether this is an association or causation of better outcomes and how skill sets could/should be expanded in a uniform way throughout EMS providers.

Impact of cardiopulmonary resuscitation duration on survival from paramedic witnessed out-of-hospital cardiac arrests: An observational study. Nehme Z. Resuscitation. 2016 Jan 13. pii: S0300-9572(16)00013-7. doi: 10.1016/j.resuscitation.2015.12.011. [Epub ahead of print]

It’s a common thought ‘how long is too long when it comes to resuscitation, is there a point at which you can safely draw a line in the sand and say that enough is enough?

This paper, lead author Nehme, is an accepted manuscript from Resuscitation will not quite give us the answer – boooo! But it does give a reasonable idea of how the increasing length of resuscitation affects the prognosis.

So this was a retrospective review of the EMS witnessed out of hospital cardiac arrests (OOHCA) from the Victorian Ambulance Cardiac Arrest Registry over a 9 year period ending in December 2011. They were all adult patients with a presumed cardiac aetiology.

They identified a total of nearly 1,400 patients of adult OOHCA of a presumed cardiac aetiology. Of all the patients (108) receiving resuscitation for over 40 minutes only one survived to hospital discharged. The 99th centile for ROSC was 59 minutes but 32 minutes when considering the clinically more important survival to hospital discharge.

Now this is effectively commentary on a case series and this shows trend of survival associated with duration of CPR. It won’t give us a specific cut off point but it does give us more of a feel for prognosis as an arrest continues and specifically when it reaches the 30 minute mark.

Is 15 minutes an appropriate resuscitation duration before termination of a traumatic cardiac arrest? Ahttp://www.ncbi.nlm.nih.gov/m/pubmed/26774992/ case-control study. Chien CY. Am J Emerg Med. 2015 Dec 12. pii: S0735-6757(15)01060-8. doi: 10.1016/j.ajem.2015.12.004. [Epub ahead of print]

Continuing along the same line but a slightly different circumstances,  this paper from Chien published in the American Journal of Emergency Medicine looks specifically at the duration of CPR in a traumatic cardiac arrest and specifically whether 15 minutes of CPR is long enough.

You may remember from our recent podcast on the European Resuscitation Council Guidelines on Traumatic Cardiac Arrest that there is a new suggested sequence and uniform approach to the situation. The guideline suggests that as soon as the reversible causes have been addressed that resuscitation should be ceased.

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As eluded to in the previous paper an understanding of prognosis during an arrest is a powerful and useful tool. In cases of traumatic cardiac arrest the team can easily become task focussed on what many consider to be an exciting and overwhelming event to be involved in. Previous American guidelines go further than ERC and suggest the time frame of 15 minutes as the appropriate duration of resuscitation to stop during which reversible causes should be addressed. This would be useful if proven to be an indicator of futility.

This paper was a retrospective review of the EMS database in Taiwan with nearly 400 patients identified in traumatic cardiac arrest who were appropriate for resuscitation. EMS then instituted resuscitative efforts and it’s important to note that this may reflect a different level of care to that we may see in the UK with what sound in the paper like a less structured approached to the resuscitation itself in terms of algorithms and uniform approach but also in the destination to a trauma centre. So with these things considered you may expect survival rates and thus longer resuscitation attempts to be futile. The paper revealed a 2.3% survival to discharge with only a 1/3 of these having a decent neurological outcome (CPC 1-2). The specific question regarding time though revealed that of the 3 patients who achieved ROSC and a favourable neurological outcome that this occurred after resuscitative efforts of 6, 16 and 18 minutes which may be a surprise to some of us.

What does this mean for us? Well both of these papers aren’t practice changers for me, they just help inform a bit more about prognosis, so I take away the fact the we need to continue to focus on rapidly reversing pathology and physiology during resuscitative efforts, to be cogniscent that time is of the essence but also be aware that in both medical and trauma related arrests that no one is going to be able to give you a binary cut off (time-wise) of futility.

External Validation of the Manchester Acute Coronary Syndromes Decision Rule. Carlton E. Acad Emerg Med. 2016 Jan 23. doi: 10.1111/acem.12860. [Epub ahead of print]

So many of you may have heard of the MACS decision rule published which was published a couple of years ago in Heart. It stands for the Manchester Acute Coronary Syndromes decision rule and was both a derivation and validation of a new decision rule with an aim to ruling out ACS with a single blood test on presentation to the ED. The blood test in question is not the loveable troponin, but h-FABP which stands for heart type fatty acid binding protein.

The authors conducted the trial due to the relatively low sensitivity of troponin and therefore the large number of false positives it identifies, the need for serial troponin and also the fact that troponin negative patients can still require revascularisation in the absence of a troponin bump.

MACS seeks to find a ‘very low risk group’ for ACS that can then be discharged home from ED, saving on patient admission, false positives and heath economics. It combines not only h-FABP at the time of presentation but a number of other markers such as sweating, vomiting associated with the pain, hypotension, worsening angina and pain radiating to the right arm and shoulder.

The requirement for further external validation was qualified due to the similar characteristics between the derivation and validation therefore bringing into question the external validity.

So they recruited just under 800 patients with a prevalence of 10% for MACE in a single centre study in Poole in England between 2012-2013. The patients studied were consecutive adult patients with suspected ACS in whom the clinician thought inpatient investigation was required. Those with high risk features such as LBBB, ECG changes consistent with ischaemia, arrhythmias and those over the age of 80 were excluded. They took serum sample for high sensitivity troponin and h-FABP and they looked at the major adverse cardiac events occurring at 30 days which included AMI, death or revascularisation.

17% of patients were as suitable for a discharge with utilisation of the MACS decision rule, these patients had a 0% incidence of MACE at 30 days or MI.

Although only a single centre study this falls in line with the previous validation of the MACS rule and shows great promise at identifying a significant proportion of patients who currently get inpatient work ups for ACS as immediately dischargeable.

As the authors state in the paper an RCT  is now justified to establish the utility of the rule in every day practice, so one would imagine we should continue to watch this space!!

 

So that’s it for this month, let us know any thoughts of feedback and we’ll be back in a couple of weeks with another podcast for you.

Simon

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