G-CUT: A 3-step transverse ultrasound approach to identify the cricothyroid membrane in a subject with large neck circumference

Abstract

Accurate and quick identification of the cricothyroid membrane plays a crucial role in management of the difficult airway especially in an emergency situation. Successful identification of the cricothyroid membrane by anaesthetists based on landmark palpation is very poor.(1Elliott DS Baker PA Scott MR Birch CW Thompson JM Accuracy of surface landmark identification for cannula cricothyroidotomy.Anaesthesia. 2010; 65: 889-894Crossref PubMed Scopus (131) Google Scholar, 2Lamb A Zhang J Hung O et al.Accuracy of identifying the cricothyroid membrane by anaesthesia trainees and staff in a Canadian institution.Can J Anaesth. 2015; 62: 495-503Crossref PubMed Scopus (52) Google Scholar) There is an emerging evidence about the role of dynamic ultrasound in cricothyroidotomy and its applicability in a can‘t intubate, can't oxygenate (CICO) situation.(3Barbe N Martin P Pascal J Heras C Rouffiange P Molliex S Locating the cricothyroid membrane in learning phase: value of ultrasonography? (French).Ann Fr Anesth Reanim. 2014; 33: 163-166Crossref PubMed Scopus (18) Google Scholar, 4Kristensen* M.S. Teoh W.H. Rudolph S.S. Tvede M.F. Hesselfeldt R. Brglum J. Lohse T. Hansen L.N. Structured approach to ultrasound-guided identification of the cricothyroid membrane:a randomized comparison with the palpation method in the morbidly obese.Br J Anaesth. 2015 Jun; 114: 1003-1004Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar) We have developed the Guildford Cricothyroid Membrane Ultrasound Technique (G-CUT), a simple and stepwise transverse approach to identify the 3 key structures (thyroid cartilage, cricothyroid membrane and cricoidcartilage) following a brief training session. We then evaluated its effectiveness by investigating accuracy and speed of identification of thecricothyroid membrane in a subject with body mass index (BMI) 32. We also assessed usefulness and acceptability of this technique and teaching bundle offered to senior anaesthetists. 27 senior anaesthetists (specialist trainees ST5-ST7, non-consultant career grade, and consultant anaesthetists) from a single center participated in this prospective single point observational study. Local research and development approval was gained; all participants read and signed consent forms. The cricothyroid membrane of a single NHS staff member subject (BMI 32; neck circumference 51cm) was pre-marked with invisible UV pen and covered with Tegaderm. Participants then marked the cricothyroid membrane puncture site with a marker pen; first using landmark technique, secondly using ultrasound (untrained), thirdly using ultrasound after the G-CUT structured training session. Training took 10 minutes, focusing on rapid stepwise identification of the Cricothyroid membrane. (Figure 1) Time needed to identify the membrane from the start of scanning to placing a mark on the neck and accuracy of identification was noted. The identification was considered to be successful if the participants' mark was between the upper and lower border of the cricothyroid membrane (previously marked with an invisible ink) and within0.5 cm from the midline. Anaesthetists graded their confidence, ease of identification of the membrane and preferred method, by completing an anonymous questionnaire between each of the attempts in the cycle. Figure 1 With a traditional landmark method, only 9 out of 27 senior anaesthetists (33%; 95% confidence interval (CI);18-52%) were able to locate the cricothyroid membrane successfully in a median time of 14.56 s[3-46] whereas 19 out of 27 anaesthetists (70%; CI 51- 84%,) identified the membrane successfully with ultrasound without any training (median of 41.09s[9-114]). The G-CUT technique with ultrasound in the transverse plane improved accuracy significantly as 26 out of 27 anaesthetists identified the cricothyroid membrane successfully(96%, CI 82- >99%) with a median of 34.01s[14-122]. There was a significant improvement in the scoring of participants' confidence (p=0.012) and ability (p=0.009) to identify the cricothyroid membrane from prior to G-CUT training (median 7/10) and after the training(median 8/10). We conclude that the G-CUT technique significantly improves the success rate of identification of the cricothyroid membrane and this training method has a positive impact on training in a short timeframe. This simple 3 step transverse approach to identification of the cricothyroid membrane can be used to identify this structure before induction of anaesthesia in patients with anticipated difficult airway. Recently published guidelines by the Difficult Airway Society recommend that one should consider using ultrasound to identify the cricothyroid membrane for the ultimate rescue plan for oxygenation via the cricothyroidmembrane.(5Frerk C. Mitchell V.S. McNarry A.F. Mendonca C. Bhagrath R. Patel A. O'Sullivan E.P. Woodall N.M. Ahmad I. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults.Br. J. Anaesth. 2015; 115: 827-848Abstract Full Text Full Text PDF PubMed Scopus (1148) Google Scholar) A positive impact of the G-CUT training method in a short timeframe with respect to skill acquisition and acceptance by anaesthetists may indicate its possible role in such emergency situations. Conflict of Interest: