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I was pleased to read recently another article on the issue of transtracheal ventilation via cricothyrotomy (Craven & Vanner, Anaesthesia 2004; 59: 595–9). The paper highlighted the success of a number of devices over a range of model lung upper airway resistances. The authors concluded that the Melker 6 mm ID cannula (Cook Critical Care, Bloomington, USA) should be the ‘technique of choice for emergency transtracheal ventilation’. They showed that the most universally effective transtracheal ventilatory device using their model was, in fact, a 6 mm ID cuffed tracheal tube, but concluded the high incidence of complications of insertion made it less favourable. There is some evidence to support their claim that the Melker kit, which was their second best ventilatory device, scores highly in terms of ease of insertion [1].

My first point relates to the issue of insertion, both generally speaking and specifically in relation to the Melker kit. The anaesthetist performing the cricothyrotomy, in probably his/her first ever ‘can’t intubate, can't ventilate' (CICV) scenario is in a very stressful situation. Successful oxygenation will only occur if the airway device is sited in the trachea. Insertion must be simple and, ideally, should have been practised. My experience of training in the use of the Melker kit on airway mannequins and animal cadavers is that its insertion is far from intuitive. It involves appropriate assembly of the kit prior to commencing membrane cannulation and several steps which are time-consuming. The cannula in the kit is of poor quality with a tendency to shear and kink. The technique is ‘surgical’, involving a scalpel incision and the creation of a large tracheal hole, making it technically challenging and unfamiliar for most anaesthetists. Furthermore, it is not universally accepted that uncuffed tubes such as this provide adequate ventilation in patients. In a recent letter [2] distinguished airway-interested anaesthetists stated that ‘the use of uncuffed 4-mm tubes should no longer be recommended for the management of “can’t intubate, can't ventilate”. Their concern is that such devices may fail in cases where the upper airway is relatively clear and lung compliance is low. I have witnessed failed ventilation in the former situation when an uncuffed 5-mm tube was used.

My second point is that I feel we should be advocating the use of needle cricothyrotomy as the first technique in the CICV scenario, largely because it is a relatively easy procedure that can be taught. In my opinion, the best device currently available is the Ravussin 13G cannula (VBM Medizintechnik GmbH, Sulz, Germany), primarily due to its simplicity and shape. I use the device electively and in emergency cases (over 50 cases in total) in awake patients in whom a dangerous GA induction or extubation or both is anticipated. Most of the senior trainees in our department are now familiar with the cannula. We use it in conjunction with the Manujet ventilator (VBM Medizintechnik GmbH).

Craven & Vanner stated that upper airway obstruction causing problems with exhalation is relatively common in the CICV scenario (they quote a figure of 14%) and they demonstrated the failure of needle cricothyrotomy devices, such as the Ravussin cannula, in such a situation. In my opinion, not only is this overstating the problem, but by employing techniques for maximising upper airway patency such as simple airway manoeuvres, airway adjuncts or the use of a laryngoscope, exhalation is unlikely to be a problem. In the rare scenario of complete upper airway obstruction, such as life-threatening laryngospasm, the option for converting a needle technique to a more invasive surgical technique always exists. In such a scenario, I would favour the ATLS teaching of a size 5 or 6 cuffed tracheal tube [3] as its insertion involves a relatively simple technique and, as the study showed, it is a very effective mode of ventilation.

The authors state that the choice of emergency tracheal access technique ‘largely depends on operator experience and equipment availability’. As most anaesthetists have little or no experience in this area, I would suggest that needle cricothyrotomy can be taught much more easily than largely ‘surgical’ techniques. I have demonstrated needle cricothyrotomy on mannequins (without leaving a great big hole), on awake ‘difficult airway’ patients and as part of the provision of airway anaesthesia prior to awake fibreoptic intubation. In terms of equipment available within our departments, we must ensure that the transtracheal airway equipment is not only effective at providing ventilation, but simple to use, deliberately limited in choice and familiar to all anaesthetic staff.

References

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A reply

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Thank you for the opportunity to reply. The Melker kit is now preassembled and the Seldinger wire should be inserted through the needle supplied, not the small cannula as the latter does kink. A scalpel incision through the skin should be made before the needle is inserted so that the wire is through the skin. The Seldinger technique is familiar to all anaesthetists and indeed the Melker kit is very similar to the percutaneous tracheostomy devices that many anaesthetists and trainees are now familiar with. At the Difficult Airway Society (DAS) workshop in Glasgow last year, anaesthetists had few problems inserting the Melker into mannequins on their first attempt. Another advantage of the Melker is that the normal anaesthetic circuit can be used on its 15-mm connector, unlike needle cricothyrotomy, which needs a high pressure jet injector like the Manujet or the Sanders devices. Availability of these injectors may be a problem in an emergency and in our opinion there is no place for devices cobbled together with tubing and 3-way taps.

In our experience (R.V.) the uncuffed 6-mm ID Melker cricothyrotomy tube was satisfactory in ventilating the lungs in the emergency situation. Occluding the nose and mouth would improve ventilation if necessary, as discussed in our article, but was not needed in this case. Cook now manufacture a Melker cricothyrotomy kit with a cuffed 5-mm ID tube that is inserted in the same way and looks promising. Although the ease of insertion in humans has not been evaluated, its insertion in mannequins did not seem to be any more difficult than the uncuffed Melker by anaesthetists at the DAS workshop.

We would not want to discourage Dr McGuire or anyone else from using needle cricothyrotomy and jet ventilation in the emergency situation, especially with his experience in this technique. However, if ventilation is impossible due to upper airway obstruction we would suggest conversion to the Melker device by passing the Seldinger wire through the Ravussin cannula, which is already in the trachea, rather than a surgical cricothyrotomy recommended in the ATLS course. A scalpel incision of the skin would still be needed but after the wire is placed. As our study showed, the uncuffed 6-mm ID tube performs well with upper airway obstruction.

R. Vanner and R. CravenGloucestershire Royal Hospital Gloucester GL1 3NN, UK E-mail: rgvanner@rgvanner.freeserve.co.uk