Ultrasound

Abstract

Editor, We read with great interest the paper by Dinsmore et al.,1 and while we congratulate the authors for their original idea, anatomical model and working methodologies, we would like to express some concerns. The first issue concerns the model. The authors fixed a depth of 28 mm according to Ezri et al.2 This could be a limitation because in the obese, ‘difficult’ patient, this distance can be even higher and because the anatomical model considered a ‘cut of beef’, not including – unless undeclared – fat tissue (such in the obese neck), which is known to have different reflecting properties to ultrasound.3 We might also argue that different results (time to performance, ease in neck puncture) could have been observed if using a dedicated set for tracheal puncture such as ETACS (Cook, Bloomington, USA), which is a little bit larger (13G) and made with slippery pre-lubricated material, rather than a generic 14G cannula. The second issue concerns time. The duration of the procedure was really long considering that the ultrasound apparatus was pre-prepared and the cannula was pre-assembled.1 In real life, a personnel experienced in ultrasound technique will take 15–20 s to prepare and boot the ultrasound apparatus, with an additional 5–10 s to prepare the neck, 10 s at least to set up the tracheal puncture device and about 60 s to perform the ultrasound-guided cannula insertion. Thus, in total, 85–100 s for the ultrasound technique and 140–160 s if using a blinded technique. During a ‘cannot ventilate – cannot intubate’ scenario, even seconds are critical, and such a time could be reasonably too long, especially if compared with Wong's results, in a mannequin model, of 40 s.4 The third issue concerns the concept. This is not about the method, which looks fascinating and reliable, but the idea that prevention is better than treatment! So, probably, it would be much more important to identify a patient at risk for difficult intubation and, even more, for difficult ventilation5 and plan an awake fibreoptic technique rather than running the risk of a ‘cannot ventilate – cannot intubate’ scenario even if the ultrasound machine is pre-booted and the airway cannula pre-assembled! Unidentifiable neck landmarks, together with difficult intubation/ventilation stigmata, should represent a critical scenario making an awake intubation technique mandatory, not forgetting risks and potential complications even in a well done (ultrasound guided or not) tracheal puncture. Recommendations of the Italian Difficult Airway Study Group do not include a fibreoptic flexible bronchoscope as a mandatory device for difficult airway management, so how can we imagine an ultrasound machine (mandatory or not) to be part of an airway cart?5 Having a portable ultrasound machine is probably for the future when technology will surely be cheaper and airway carts probably larger. To conclude, we believe there will increasingly be a place for ultrasound in anaesthesia practice. Developing dedicated skills will be of paramount importance in the setting of pre-operatory evaluation (ultrasound as a decisional tool to ‘graduate’ airway difficulty and to identify preliminary landmarks) or even more so in the setting of percutaneous tracheostomy in the ICU (pre-tracheal vessel identification, tracheal position, needle placement). If thinking of a potential ‘cannot ventilate – cannot intubate’ scenario, probably not ultrasound, but ultrasafety should be the choice.