Over the last few years there has been much effort and a fair bit of #FOAMed activity around ensuring that RSI in critical environments is as safe and efficient as possible. Concepts such as first pass success1, apnoeic oxygenation2–4, positioning5, bougies6,7 and more have all aimed to promote safe practice. An overarching principle behind these innovations and adaptations is the aim of preventing peri-intubation hypoxia and hypotension.
Hypoxia is always a risk for our critically unwell patients. The RSI sequence arguably promotes hypoxia through the use of paralytics that cause apnoea. The apnoea between induction, to laryngoscopy, to intubation, to then ventilation, make hypoxia likely in a group of patients who are often difficult to pre-oxygenate, who have less physiological reserve than the average routine theatre case and who may have excessive oxygen demands (think agitated delirium8). Hypoxia is more common in the ED and the ICU, and the consequences may be significant.
Why then do we stop ventilating during the apnoea phase of RSI?
For many years I have seen some of my colleagues routinely ventilate patients at risk of desaturation in the time between induction and paralysis taking effect. We typically do this using a Water’s circuit with a bit of PEEP applied (that’s a Mapleson C circuit) which we use for pretty much all RSIs in Virchester). In pre-hospital care there is a preference for the BVM as it still works even if you lose your O2 supply. It’s done gently and carefully to avoid gastric insufflation, but it’s always felt a little odd as we I was originally taught that ventilating at this stage of the RSI was forbidden and dangerous. Notably because it was felt that it could induce aspiration. On the other hand there are the risks of desaturation, hypoxia and the associated consequences of cardiovascular instability and potential end organ damage. Thus the debate about whether ventilating the patient in the time between induction and intubation has been controversial and debated for years9–12.
To get some clarity here, think of a patient who is already on the edge of desaturation, the septic patient with pneumonia who is really struggling. The best you can get their O2 is 95% before you start and they are clearly working hard (with a presumed high O2 demand). Even with good apnoeic oxygenation adjuncts, good pre-oxygenation and other first pass optimisation techniques you know that this patient may well crash their O2 saturations on induction. Should you really stop ventilating that patient for the 20-60 seconds it’s going to take for the paralytics to take effect PLUS the time it then takes you to get an airway and then ventilate the patient? Realistically this person may have a ventilatory pause of 60-120 seconds. Hang on, they look a bit tricky to intubate too. Maybe that 120 seconds will be an ambitious target……..
Does a prolonged ventilatory pause seem such a good idea now?
This week we have a paper that hopes to answer the question of whether there are potential advantages, and also whether there are any potential harms to ventilating a patient throughout the RSI induction process. Published in the NEJM13, the abstract is below, but as always we strongly advise you to read the full paper, perform your own critical appraisal and make your own mind up.
What kind of paper is this?
It’s a randomised controlled trial. As this is a study of an intervention this is the best design to test this.
Tell me about the patients.
This study is a multicentre study of ICU patients in the US. Adults were included in the paper who required endotracheal intubation in the ICU for whatever reason. The common exclusions (such as pregnancy and prisoners) applied.
What was the intervention?
Patients in the study group were ventliated using a bag mask valve (BVM) with a PEEP valve in the interval between induction and laryngoscopy. The control group did not receive ventilations. Ventilations were gentle (just to see the chest rise) and at a rate of about 10/minute.
Interestingly in the UK we tend to use the BVM less and the Water’s circuit more. The amount of PEEP applied using a Water’s circuit is a bit of an art rather than a science and certainly does not allow a quantifiable value.
The rest of the RSI was not standardised and pretty much left to the discretion of the physician, although there were few differences in terms of medications used.
What were the outcomes?
The key outcome was the median lowest oxygen saturation (as defined by an SaO2 of <90%) after induction and up to 2 minutes post intubation.
They also looked for any evidence of aspiration at laryngoscopy and from looking at new opacities on the chest Xray within 48 hours of the procedure.
What are the main results?
The authors recruited 401 patients into the trial. The patients were pretty similar at baseline but there were statistically more patients with pneumonia and GI bleeds in the no ventilation group. This may be important as pneumonia patients are at particular risk of desaturation during induction. Patients in the BVM group had more BVM ventilation pre induction as compared to the non-ventilated group. Presumably because once enrolled the airway operator in the BVM group would have had the device in their hands and ready to go. It is unclear then if pre-induction BVM may have influenced the results.
For the primary outcome of median lowest oxygen saturation then patient’s did better in the BVM group with a median O2 sats of 96% as compared to 93% in the non ventilated group.
However, when I look at trials like this I am less interested in average scores as to be honest if all patients stayed at >92% I’d probably be arguing that it’s clinically not important. What I am interested in is the number of patients who have significant desaturations during RSI.
There was more desaturation below 90% in the non ventilation group (40.1%) as compared to the BVM group (29.5%). However, the image below from the paper, and released on twitter is really the key to understanding just how different the groups were.
The key point is the increased number of patients who have very significant desaturations between the two techniques. The increased number of extreme desaturations is, for me, the strongest argument of the paper and also a reminder that looking at the raw data wherever possible and not just the summary statistics is an important part of critical appraisal. If you prefer your data as a bar chart then here you go.
Again, this data suggests that there were far fewer clinically significant desaturations in the BVM group.
There were no increase in the number of complications (aspiration) in the BVM group.
So we should all bag away with gay abandon during an RSI then?
There are always caveats. The data here is by far the best that we have so far but we need to be thoughtful if we wish to adopt this. Patients in the BVM group may have been more effectively pre-oxygenated (through use of BVM) as much as by BVM in the apnoeic phase and this needs to be taken into account, but personally I think that’s likely to be less of a factor.
The technique of BVM in this study was carefully applied and gentle. This needs skill and care and is may not be in the skill set of all airway practitioners (sorry, but it’s true). Face mask ventilation is not that easy (although many people think it is). In this study a two person, two handed technique was used and so it’s not just a case of putting a BVM on the face and expecting similar results. Use of the Water’s circuit, as we do in Virchester, raises the skill levels required even further.
In the UK we generally use Water’s circuits more often than BVM. On those occasions when we do use BVM then we often don’t have PEEP valves. Would we therefore get the same results with those technique modifications as compared to the paper? Probably, but we don’t really know. Personally I think that PEEP is probably as important as the ventilation in these patients. PEEP maintains alveolar recruitment which may be the key pathophysiological mechanism underpinning the difference in the results.
I would strongly recommend, in fact I would insist that if you are thinking of adopting this in your practice then you read the excellent blog by Josh Farkas on the EMCRIT site14. It gives an excellent explanation of this trial and the underlying physiological principles. Please read this before concluding your thoughts on this trial.
Finally, as an ED clinician it’s important to remember that these are critical care patients and whilst they will share similar characteristics to the patients I see in the ED, they are not quite the same.
Should we adopt this practice?
So in Virchester, for those patients in whom desaturation is a risk/concern, and where some additional precautions are possible (e.g. head up positioning) then I would advocate very gentle ventilatory support during the period between induction and laryngoscopy.
Although this study used a BVM with PEEP valve I will continue to do this using a Water’s circuit with a ‘bit’ of PEEP, during both the preoxygenation and post intubation phases of RSI.
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- 1.Sakles JC, Chiu S, Mosier J, Walker C, Stolz U. The Importance of First Pass Success When Performing Orotracheal Intubation in the Emergency Department. Reardon RF, ed. Acad Emerg Med. January 2013:71-78. doi:10.1111/acem.12055
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