The guidelines for management of a difficult airway recommend incision or puncture of the CTM in a CICO situation. However, the fourth National Audit Project  reported that surgical securing of the airway under anesthesia in such circumstances had a 43% risk of serious complications.
Cricothyroidotomy by incision of the CTM is more reliable than puncture, and its success depends on correct identification of the CTM . However, the CTM may be difficult to identify by the conventional palpation technique if it is not in the normal anatomical location . In the present case, the otolaryngologist could not identify the superior thyroid notch by palpation because of the overlying hematoma. The conventional palpation technique is usually started from the superior thyroid notch as an anatomical landmark. Ultrasonographic guidance may have an advantage over conventional palpation for identifying the CTM in the event of an anatomical abnormality .
In our case, the CTM could not be identified by the widely used transverse ultrasound approach  because the patient’s hematoma extended from the mandible to the upper neck. The superior thyroid notch could not be identified by palpation, so the anesthesiologist started to scan from the patient’s lower neck. A longitudinal ultrasound approach has been described but its efficacy is thought to be limited because the ultrasound probe cannot be positioned correctly on the skin surface in a patient with a short neck or severe cervical flexion deformity . Kristensen et al. reported that the transverse and longitudinal approaches for ultrasonographic identification of the CTM in obese female subjects had a 90% success rate for identifying the CTM . Interestingly, they found that neither approach was inferior to the other for identification of the CTM in obese patients . The anesthesiologists’ first choice in the report by Kristensen et al. was a transverse approach because they were familiar with it and unfamiliar with the longitudinal approach. However, our anesthesiologists could identify the CTM using the longitudinal approach but not the transverse approach. In our patient, the CTM was deep below the skin surface, which made it difficult to locate using the transverse approach because of the narrow searching space between the thyroid cartilage and the cricoid cartilage (Fig. 3).
Siddiqui et al. reported that ultrasonography successfully identified the CTM even in cadavers with poorly defined neck anatomy and speculated that ultrasonographic identification may reduce complications and improve the success rate of cricothyroidotomy . The 2015 UK Difficult Airway Society guidelines recommend preoperative use of ultrasonography for identification of the CTM to ensure successful cricothyroidotomy in patients anticipated to have a difficult airway  but not otherwise, and with the caveat that ultrasonographic identification of the CTM might be unnecessarily time-consuming when the airway needs to be surgically secured in an emergency. We believe that ultrasonographic identification of the CTM is not time-consuming when performed by a skilled operator. It has been reported that competence can be achieved by a short period of hands-on training [7, 12]. Therefore, training should make reliable identification of the CTM easier and ensure successful cricothyroidotomy.
The CTM could not be found by palpation in our patient but could be identified by ultrasonography. Fortunately, awake intubation was successful in this case. However, we cannot state with certainty that cricothyroidotomy would be successful using the method described here in a patient approaching CICO after awake intubation has failed. It is difficult to conduct high-quality clinical research on the success rate of cricothyroidotomy under ultrasonographic guidance, so the efficacy of identification of the CMT using this modality is still a matter of debate. However, it was recently found that ultrasound-guided identification of the cricothyroid membrane [6, 13] is highly effective and is comparable to a CT-scan as the accepted standard  in patients with abnormal neck anatomy. This strongly indicates that this technique can be applied for patients such as the one described in this report.