Quite a few months back I was supervising a registrar intubating a patient using the C-MAC. The patient was a middle aged male who had a decreased conscious state following an OD. Apart from being somewhat overweight, there were no predictors of a difficult intubation.

Preparation and pre-oxygenation were all standard. However intubation was initially unsuccessful. The C-MAC screen showed a good (great) view of the larynx, but the registrar was unable to bring the tip of the tube into the field of view, and the tube passed down the esophagus each time it was (blindly) advanced. Attempts to intubate were ceased after the patient began to desaturate. He was easily ventilated with a bag and mask, his saturations promptly normalized, and there was no adverse outcome. So no real problem. I subsequently intubated the patient with a conventional laryngoscope, which provided a grade 1 view.

Later that evening I was having a coffee with the registrar. We tried to work out how the C-MAC had turned a grade 1 view into a patient unable to be intubated. Bearing in mind that the C-MAC is claimed to make intubation safer and easier, is promoted as an invaluable teaching tool, and some advocates claim it is now “standard of care” and predict the end of conventional laryngoscopy.

It struck me that conventional laryngoscopy is a sequential left hand and then right hand skill:

  1. You use your left hand to insert the laryngoscope and then manipulate the blade in order to provide a good view. Sure you might extend the head or externally manipulate the larynx with your right hand. But it is primarily a left hand task. Once you have a good view, you often relax a bit. Nothing can go wrong now. Just keep that view.
  2. The act of passing a tube (or bougie) using your right hand – while keeping your left hand still so as to maintain your view.

I believe this is almost a subconscious process reinforced over the years. Get a view with your left hand, keep your left hand perfectly still, and then intubate the patient. Simple.

If you use the C-MAC as a conventional scope (ie you use direct vision to look down the mouth and don’t look at the screen), then the above still holds.

If however you look at the screen, the above all changes – possibly without you recognising it.

The C-MAC is designed to create a good view. And it does this very well. You can pretty much insert it however you want, and you will get a good view of the larynx. As seen from the lens on the blade. This may however be very different from the view you would see looking down the patients mouth – which is the path the tube has to follow. You may have a grade 1 view as seen from behind the patients tongue, but a grade 4 view using direct vision.

So now you have got a great view on the screen. Except there is now a disconnect between what you are seeing on the screen, and what happens next. You never see the tube appear on the screen. However because you still have a great view, you don’t realise you need to manipulate the blade to provide a clear path for the tube. Subconsciously, the path must be fine (and thus nothing for the left hand to do) as the view is good. I think this is what happened in this case.

I subsequently spoke to a couple of anaesthetic colleagues. They confirmed this is what most likely happened, although one explained it a little differently as “failure to control the tongue.” We have all been taught to go down the right side of the tongue and to sweep / lift it out of the way in order to obtain a clear view. You have to control the tongue. However you can skip this step using the C-MAC screen – the screen effectively puts you somewhere behind the base of the tongue and so you don’t have to control it. You have a good view even if the airway superior to the lens is obstructed by the tongue. If the tongue has fallen against the posterior pharyngeal wall, it will helpfully guide an advancing tube into the esophagus.

These anaesthetists confirmed the accepted practice when using the C-MAC is for the intubator to use direct vision. The screen is for other people to watch. The intubator not only has to have a view of the larynx, but needs to have a clear view of the entire path the tube needs to follow.


So with that long preamble, I think there is a broader issue here. New technology and new devices can certainly help us to our jobs better than before. No doubt about that. But as with this case, it can also introduce new problems or risks or traps. And these are not always immediately obvious.

The salespeople promoting the technology have an incentive to talk up the positives, rather than pointing out the potential problems (and in all fairness they may not be aware of the problems – how many C-MAC salespeople intubate patients?) And even well meaning colleagues enthusiastic about some new device (and with no commercial conflict of interest) may gloss over the dangers – perhaps because they are so obvious to them they don’t require discussion. One anaesthetist was puzzled why the registrar was ever looking at the screen in the first place – “But everyone knows you need to use it like a conventional scope.” I guess someone forgot to tell the registrar and myself.

So we need to know how to use new devices and new technology safely. This means we need to understand how it actually works, the subtle ways it can change things, and we need to be aware of the hazards and traps.

Dr Steve Walker, Staff Specialist, Nepean Emergency Department.

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