Comparison of the acromio-axillosuprasternal notch index with five anatomical indices for the prediction of difficult laryngoscopy and intubation.

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Editor, Unexpected difficult intubation leads to hazardous consequences including arrhythmias, hypoxia and cardiac arrest.1 The prediction of difficult visualisation of the larynx (DVL) is very important in airway management. Although the Cormack–Lehane grading system was accepted as a gold standard test to define difficult laryngoscopy, it can be assessed only during intubation.2 Therefore, the establishment of criteria that can predict difficult intubation before laryngoscopy is necessary. Some previous studies have assessed indices, such as interincisor gap, Mallampati test, modified Mallampati test (MMT), thyromental distance (TMD), sternomental distance, ratio of patient's height to TMD (RHTMD), BMI, neck circumference, ratio of neck circumference to thyromental height (neck circumference/TMH), upper lip bite test (ULBT) and acromio-axillo-suprasternal notch index (AASI). They found that these indices had different levels of sensitivity and specificity for prediction of difficult intubation.3–9 We compared the predictive values of six anatomical indices (TMH, AASI, MMT, ULBT, RHTMD and neck circumference/TMH in DVL) with respect to difficult intubation and laryngoscopy to find out which test had the highest predictive value. The current cross-sectional study was approved by the Ethics Committee of Isfahan University of Medical Sciences (IR.MUI.REC.1394.3.046) and conducted in Al Zahra Hospital affiliated with Isfahan University of Medical Sciences in Iran from May 2016 to February 2017 in 600 patients undergoing surgical procedures under general anaesthesia. Patients were included if they were aged between 18 and 70 years, candidates for surgical procedures (except caesarean section) under general anaesthesia, BMI less than 30 kg m−2, absence of anatomical airway disorders, cervical fractures, upper airway trauma, cervical, mandibular rheumatological diseases, pathological defects in the upper airway, obstructive sleep apnoea and no history of difficult intubation. Patients who required more than one attempt at tracheal intubation, an additional operator or an alternative intubation technique, a considerable lifting force during laryngoscopy, external pressure on the larynx for improving glottic exposure and vocal fold adduction at intubation were excluded from the study. All patients were subjected to measurement for the above indices prior to admission to the operating room. According to the laryngoscopic view graded by the Cormack–Lehane grading system, the anaesthesiologist divided the patients into two groups of easy or difficult regarding the intubation process. In this classification system, grades 1 and 2 were considered as easy, whereas grades 3 and 4 were defined as difficult intubation.1,4,8–10 From induction until the end of anaesthesia, standard devices monitored ECG, pulse oximetry and blood pressure. The data were analysed using SPSS software (version 20.0; SPSS 20, IBM, Armork, NY, USA) by analysis of variance, receiver-operating characteristic (ROC) curves, the χ2 test, and diagnostic value tests with the confidence level of 95%. Comparison between area under the curve (AUC) of six tests was performed using MedCalc software 9.2.0.1 (MedCalc Software, Mariakerke, Belgium). A total of 600 patients undergoing general anaesthesia were included in the study. No intubation failure was reported during the study. All results are presented in Tables 1–4. Table 3 shows the AUC cut-off point, confidence interval and level of significance related to six indices according to the Cormack–Lehane test. It revealed that neck circumference/TMH, TMH and AASI had the highest AUC of ROCs.Table 1: Demographic characteristics of all participantsTable 2: Anatomical indices in easy and difficult intubation patientsTable 3: Area under the curve of receiver-operating characteristic and cut-off point regarding assessed testsTable 4: Criteria of diagnostic values related to the assessment testsTable 4 shows that neck circumference/TMH had the highest sensitivity (80.6%) and AASI had the highest specificity (94.8%). The highest level of positive predictive value was related to the neck circumference/TMH index and the highest level of negative predictive value was related to ULBT. The highest levels of both positive and negative likelihood ratios were also achieved by neck circumference/TMH. Our findings were in line with the literature in terms of sensitivity and specificity of indices. Moreover, we found that neck circumference/TMH, AASI and TMH had higher predictive values than other airway assessment indices that can be used to determine intubation process grades in patients prior to laryngoscopy. Acknowledgements relating to this article Assistance with the letter: none. Financial support and sponsorship: we would like to thank the Vice-Chancellor for Research of Isfahan University of medical sciences for funding of this research. Conflicts of interest: none.