By Tom Heaton
First described by Sellick in 1961, cricoid pressure was originally designed to make life difficult for smart-arsed junior anaesthetic trainees that were feeling rather pleased with themselves just because they had intubated half a dozen patients. It achieved this with a potent combination of impairing laryngeal view, resisting passage of an endotracheal tube and, crucially, also making manually ventilating the patient more challenging. ‘Sellick’s Triad’, born from this simple application of cricoid pressure, was able to successfully increase the number of trainee 'brown trouser' moments and a new trend in anaesthetic practice was born.
Okay so I may have completely made this bit of history up, but this collection of complaints seems to be widely cited as being behind cricoid pressures descent from favour in recent times, especially with it’s partnering question of ‘Does it actually do anything?’ If you have been following some of the stuff at SMACC Gold through Twitter (or been lucky enough to actually attend) you might have heard some of the arguments around this increasingly controversial technique.
Okay so I may have completely made this bit of history up, but this collection of complaints seems to be widely cited as being behind cricoid pressures descent from favour in recent times, especially with it’s partnering question of ‘Does it actually do anything?’ If you have been following some of the stuff at SMACC Gold through Twitter (or been lucky enough to actually attend) you might have heard some of the arguments around this increasingly controversial technique.
The theory behind cricoid pressure seems decent enough. The cricoid is a complete ring of cartilage and if you press it posteriorly it should compress (and therefore occlude) the oesophagus against the cervical vertebral bodies, preventing regurgitation of any stomach contents. But this simple assertion has been questioned in some studies stating that lateral deviation of the oesophagus is common, and some describing cases of regurgitation despite cricoid pressure.
The final component is the notorious variability in cricoid pressure technique amongst staff performing it. A variety of pressures have been described with 30N being the current recommended amount. Whether this is the force applied, or even if this force is actually applied to cricoid cartilage rather than some other neck structure remains a recurring question.
So this leads to a position that I think is nicely reflected in the borrowed quote below:
The final component is the notorious variability in cricoid pressure technique amongst staff performing it. A variety of pressures have been described with 30N being the current recommended amount. Whether this is the force applied, or even if this force is actually applied to cricoid cartilage rather than some other neck structure remains a recurring question.
So this leads to a position that I think is nicely reflected in the borrowed quote below:
'As a profession we invest a great deal of importance in a technique that is inadequately researched, poorly taught and badly performed' (Haslam & Duggan 2004)’
I would add to this that it makes life difficult for those managing the airway (myself very much included) and adds a little bit of extra stress just when you’d rather not have it.
With that quite extensive preamble done I think it is time to turn to the article that was actually meant to be the focus of this post. Appearing in the March 2014 edition of Anesthesia and Analgesia you can get to the paper through the link below.
With that quite extensive preamble done I think it is time to turn to the article that was actually meant to be the focus of this post. Appearing in the March 2014 edition of Anesthesia and Analgesia you can get to the paper through the link below.
What's It About?
This nice little study tried to assess the effectiveness of properly performed cricoid pressure in occluding the oesophagus of anaesthetised patients. This was assessed by whether or not it was possible to pass a 20 French or 12 French sized gastric tube in the presence and absence of cricoid pressure using a glidescope (type of video laryngoscope) to visualise the glottis and oesophageal opening. The cricoid pressure of 30 N was applied by a well practised operator who hand undergone 20 successive and successful practices of applying the correct force (+/- 2 N). Each patient had attempts at passing the tubes both with and without cricoid pressure with the attempt order randomised. They also had a look at the video they obtained after the study to further assess what the cricoid pressure was doing to the different structures.
What Did They Find?
They included 79 patients in the study (41 men and 38 women) after a power calculation to determine that they would need at least 72 patients. In all the attempts when cricoid pressure was applied it was not possible to pass the gastric tube. In all the attempts when cricoid pressure wasn’t applied the gastric tube was passed easily (under 5 seconds). Wow, not sure it gets more barn door than that as a primary finding.
In terms of the other findings from the study the authors note from the video recordings that cricoid pressure did cause narrowing of the laryngeal opening and apposition of the cords in 30 of the patients, though there was no difficulty passing the ETT in any of these patients (sizes 7.0 and 7.5mm ID). The laryngeal opening was to the left side of the patient in respect to the glottis in 57% of the patients and in the midline in 32%, with no change in this position with cricoid pressure.
In terms of the other findings from the study the authors note from the video recordings that cricoid pressure did cause narrowing of the laryngeal opening and apposition of the cords in 30 of the patients, though there was no difficulty passing the ETT in any of these patients (sizes 7.0 and 7.5mm ID). The laryngeal opening was to the left side of the patient in respect to the glottis in 57% of the patients and in the midline in 32%, with no change in this position with cricoid pressure.
Is It Any Good?
I have to say that I think the methodology of the study, within the limits of the study’s nature, was pretty well thought out and conducted. Both the operators applying cricoid and trying to pass the tube were blinded to what the other was doing by a screen and the order of application of pressure was randomised. The anaesthetic given to each patient was carefully standardised, as were the majority of the other potential variables that I could think of; number of attempts, application of cricoid pressure, degree of neuromuscular blockade, time limit and more.
There are some obvious limits to this study, most notably the fact that this is very much a surrogate for anything useful. The smallest gastric tube had an external diameter of 4mm but this still doesn’t tell us much about the effect on liquid stomach contents and their ability to regurgitate. Even though the 2 main operators were both blinded to each others actions, the authors report a visual difference of the oesophageal opening when cricoid pressure was applied that may have compromised the blinding for the operator passing the gastric tube. I also feel that the limitations applied to the patients involved in the study takes some of the edge of the applicability to real clinical practice, as these were all relatively slim, healthy patients without reflux symptoms. There were also a number of patient excluded (28 in total) due to the fact that visualisation of the oesophageal opening was a requirement to continue with the study. Though reasonable, it’s not quite clear to me whether there were any special characteristics of these patients which could have introduced bias, as little is said about them.
There are some obvious limits to this study, most notably the fact that this is very much a surrogate for anything useful. The smallest gastric tube had an external diameter of 4mm but this still doesn’t tell us much about the effect on liquid stomach contents and their ability to regurgitate. Even though the 2 main operators were both blinded to each others actions, the authors report a visual difference of the oesophageal opening when cricoid pressure was applied that may have compromised the blinding for the operator passing the gastric tube. I also feel that the limitations applied to the patients involved in the study takes some of the edge of the applicability to real clinical practice, as these were all relatively slim, healthy patients without reflux symptoms. There were also a number of patient excluded (28 in total) due to the fact that visualisation of the oesophageal opening was a requirement to continue with the study. Though reasonable, it’s not quite clear to me whether there were any special characteristics of these patients which could have introduced bias, as little is said about them.
Final Thoughts
I have to say that despite its notable limitations I was fairly impressed with the careful design of the study and it has come up with some pretty stark results. Yes the patients were carefully selected and receiving cricoid pressure with an almost scientific precision, but it is suggesting pretty strongly that the cricoid pressure is doing at least a little bit.
I don’t really like cricoid pressure. I personally find that it makes my job of airway management harder and this is something that is pretty widely recognised, and even hinted at in this study. And despite the careful attempts of the authors this is still just a study of a surrogate for regurgitation. However, protecting my patients and doing no harm is first on my priority list. This study doesn’t explicitly tell us that cricoid pressure works, but it does wriggle it’s eyebrows suggestively at you. Until there is solid data on outcome difference that I can see and feel confident with I will always end up erring towards what is probably safest for my patients, especially when the theory seems to make sense and it is still endorsed by many leading organisations. As pointed out in the Royal College of Anaesthetists'/Difficult Airway Society's 4th National Audit Project (NAP4) aspiration was the commonest cause of death reported. For now it looks like Sellick is still getting his way with us trainees. Damn!
Thanks for reading and, as always please let me know your thoughts on the topic. I know there is quite a bit of other evidence out there about that we will hopefully get round to looking at but let me know of any other links that have caught your eye. Until next time.
Tom Heaton
I don’t really like cricoid pressure. I personally find that it makes my job of airway management harder and this is something that is pretty widely recognised, and even hinted at in this study. And despite the careful attempts of the authors this is still just a study of a surrogate for regurgitation. However, protecting my patients and doing no harm is first on my priority list. This study doesn’t explicitly tell us that cricoid pressure works, but it does wriggle it’s eyebrows suggestively at you. Until there is solid data on outcome difference that I can see and feel confident with I will always end up erring towards what is probably safest for my patients, especially when the theory seems to make sense and it is still endorsed by many leading organisations. As pointed out in the Royal College of Anaesthetists'/Difficult Airway Society's 4th National Audit Project (NAP4) aspiration was the commonest cause of death reported. For now it looks like Sellick is still getting his way with us trainees. Damn!
Thanks for reading and, as always please let me know your thoughts on the topic. I know there is quite a bit of other evidence out there about that we will hopefully get round to looking at but let me know of any other links that have caught your eye. Until next time.
Tom Heaton
Some nice links
- Life In The Fast Lane - LITFL have their own review of cricoid pressure with a good selection of links to check out
- PHARM - Pre Hospital and Retrieval Medicine reflect on cricoid pressure (they have also had a more recent look at this paper)
- Difficult Airway Society - The DAS Guidelines on RSI
- Best BETs - The Best BETs review of cricoid pressure
- NAP4 - The 4th National Audit Project has some interesting reading on aspiration and airway management
- PHARM - Pre Hospital and Retrieval Medicine reflect on cricoid pressure (they have also had a more recent look at this paper)
- Difficult Airway Society - The DAS Guidelines on RSI
- Best BETs - The Best BETs review of cricoid pressure
- NAP4 - The 4th National Audit Project has some interesting reading on aspiration and airway management
And some other papers on the subject
- Anaesthesia (2000) - The effect of cricoid pressure on the cricoid cartilage and vocal cords
- Anesthesiology (2003) - Cricoid Pressure Displaces The Esophagus
- Anesthesiology (2003) - Cricoid Pressure Displaces The Esophagus
Image courtesy of David Castillo Dominici/FreeDigitalPhotos.net
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