Prophylactic percutaneous transtracheal catheterisation

Abstract

Gerig et al. outline their experience of prophylactic percutaneous transtracheal catheterisation in the management of patients with anticipated difficult airways [1]. We wholeheartedly agree that usually this is a straightforward and elegant method of avoiding life-threatening hypoxia in patients with anticipated difficult airways. In their description of the technique, however, they state that the correct position of the transtracheal catheter should be confirmed by the free aspiration of air through the catheter. Whilst we agree that this part of the procedure is vital and must be performed assiduously, we would like to point out that we recently discovered that this test does not confirm, with certainty, the correct placement of a transtracheal catheter. The correct position of the catheter is within the airway and with the catheter directed caudally. A cephalad directed catheter will not oxygenate a patient and jet ventilation through the same may damage an already jeopardised airway. Aspiration of air merely confirms that the catheter tip is within the airway. A cephalad position of the transtracheal catheter occurs when the catheter kinks in the airway as it is rail-roaded off the needle and this is recognised to happen in up to 20% of catheterisation attempts [2, 3] and even purpose-made Teflon (which are more kink-resistant than plastic) cricothyrotomy cannulae do not eliminate this complication [4]. We recently performed a percutaneous cricothyrotomy on a patient in our ICU. A 6.0 mm Melker Emergency Cricothyrotomy Catheter (Cook Europe Ltd, Bjaeverskov, Denmark) was used and the patient had a normal airway. The 18G cannula-over-needle from the Melker set was inserted at an angle of 30–40° to the frontal plane, caudally through the cricothyroid membrane, and air was freely aspirated. The cannula was easily railroaded and the needle removed. Air was again aspirated from the cannula and the guidewire passed smoothly. The patient coughed at this point. The Melker catheter, mounted on its trochar, was easily passed to its full depth over the wire. The patient remained stable, but we were unsure of its position because we couldn't aspirate sputum and so a CXR was arranged. This clearly demonstrated the cephalad direction of the catheter (which was then removed uneventfully). The initial cannula must have kinked and become ‘north’ facing at insertion [5]. In the Melker set – which has been recommended for emergency transtracheal ventilation [6]– there are two methods of gaining access to the sublaryngeal space: one is an unsheathed 18G needle, through which a guidewire can be passed, and the alternative is an 18G cannula. Expert opinion suggests that such misplacement can be minimised by passing a guidewire through the unsheathed needle, so avoiding the use of the cannula, which may kink [7]. For transtracheal catheterisation, we have used a wire-through-needle Seldinger technique with a 14G transtracheal catheter (VBM, Sulz, Germany). We insert the VBM needle (loaded with the catheter as Gerig et al. do) until air is aspirated. At this point, instead of railroading the catheter into the trachea, a 0.9 mm J-shaped guidewire from a central venous line set (BD CareflowTM, Becton Dickinson Ltd, Singapore) is inserted through the needle such that about 5 cm protrudes from the needle's tip into the trachea (the VBM catheter is 4.5 cm long). The catheter is then railroaded into the airway over the wire and so follows the course of the wire caudally. The wire and needle are removed and free aspiration of air is again confirmed. No step is created between the wire and the catheter which could impede the passage of the catheter because it is the needle that guides the catheter into the trachea; the wire merely guides it caudally thereafter. This extra step takes only a short time. The technique of prophylactic placement is so potentially useful, as Gerig et al. highlight, that every effort should be made to ensure correct positioning of the catheter.