Acromio-axillo-suprasternal notch index

Editor, The acromio-axillo-suprasternal notch index (AASI) (Fig. 1) was recently introduced for prediction of difficult laryngoscopy in patients who underwent surgery under general anaesthesia requiring tracheal intubation. It was shown that AASI was superior to the Mallampati classification (a conventional index) in this respect. As the one previous study has shown, patients whose neck was situated deep in the chest (i.e. with a sloping clavicle) had more incidences of difficult visualisation of the larynx (DVL).1 AASI represents part of the arm-chest junction, which is located above the level of the suprasternal notch (Fig. 1). It was shown that patients with AASI more than 0.5 had a higher incidence of DVL.Fig. 1: The method of measurement of acromio-axillo-suprasternal notch index (AASI). AASI was defined as the ratio of line C to line A. (a) The line was drawn from the acromion to the upper axillary fold parallel to the longitudinal axis of the body. (b) A line was drawn perpendicular to line A to the lower part of the suprasternal notch. (c) The length of line C was determined by the position of the intersection of line B with line A.No previous published study has investigated the predictive value of this index in pregnant patients, so we designed this prospective blind study for comparison of the AASI with the Mallampati classification revised by Samsoon and Young, the ratio of height to thyromental distance (RHTMD), the ratio of hyomental distance in full extention of the neck to neutral position (HMDR), the ratio of neck circumference to thyromental distance (NC/TMD) and the Upper-Lip-Bite test (ULBT) for prediction of difficult laryngoscopy in parturients candidates for caesarean delivery. After obtaining institutional approval from the Ethics committee of our university and taking written informed consent from the patients, 716 American Society of Anesthesiologists’ (ASA) physical status 1 and 2 patients scheduled for elective caesarean delivery under general anaesthesia requiring endotracheal intubation were enrolled into this prospective, comparative, double-blinded observational study. Ethical approval for this study (Ethical Committee IUMS, Project number 392547) was provided by the Ethical Committee IUMS of Isfahan University of Medical Sciences, Isfahan, Iran (Chairperson Prof P. Adibi) on 10 December 2013. The following six predictive test measurements were performed by a physician who was not involved in laryngoscopy assessment: NC/TMD: The ratio of neck circumference to TMD was calculated.2 RHTMD: TMD was measured from thyroid notch to the bony point of the mentum. Then, the ratio of height to TMD was calculated.3 ULBT: ULBT was rated as Class I if the lower incisors can bite the upper lip above the vermilion line, Class II if the lower incisors could bite the upper lip below the vermilion line, Class III if the lower incisors could not bite the upper lip.4 HMDR: The ratio of hyomental distance in full extension of the neck (HMDe) to this distance in the neutral position (HMDn).5 5-MMT: Samsoon and Young modification of the Mallampati test classifying the oropharyngeal structures visible (Class I-IV). AASI: AASI was defined as the ratio of line C to line A as shown in Fig. 1. Line A was drawn vertically from the acromion to the upper axillary fold parallel to the longitudinal axis of the body. Line B was drawn perpendicular to line A to the lower part of the suprasternal notch. The length of line C was determined by the position of the intersection of line B with line A. (Fig. 1).1 A total of 716 patients were enrolled into this study. The predictive values of all predictors are shown in Table 1. The area under the curve (AUC) of the ROC was highest for AASI in comparison with the other tests. The differences of MMT, neck circumference/TMD, HMDe, HMDn and AASI ROCs were statistically significant (P < 0.05). In discrimination analysis, AASI 0.61 or less was considered as the cut-off point in predicting DVL. AASI had the highest sensitivities among the predictors (73.4, 58.3 and 53.3%, respectively).Table 1: Predictive value for modified Mallampati test, upper lip bite test, ratio of height to thyromental distance, neck circumference/thyromental distance, hyomental distance in head fully extended with closed mouth, hyomental distance in neutral position, hyomental distance ratio and acromio-axillo-suprasternal notch index to predict the incidence of DVL according to the Cormack–Lehane classificationOur study showed that the AASI was a more accurate predictor of difficult laryngoscopy than the other tests. In the study by Kamranmanesh et al.,1 AASI had the higher predictive value in comparison with MMT in general population with a cut-off point of less than 0.5. In the present study, we found that AASI with a cut-off point of 0.6 or less and AUC of 0.697 could be the most powerful and reliable predictive bedside test for the prediction of difficult laryngoscopy in parturients in comparison with the other preoperative airway assessment tests. In our study, the AASI had the highest specificity, positive likelihood ratio, positive predictive value, negative predictive value and AUC in comparison with the other predictive tests. The AASI on its own is not dependent on patient position and it shows the intrathoracic indexices. Advantages of AASI are the use of an inexpensive and easily applicable instrument for this measurement. In conclusion, our study showed that the AASI was a powerful test for the prediction of difficult laryngoscopy in parturients scheduled for caesarean delivery. Acknowledgements relating to this article Assistance with the study: none. Financial support and sponsorship: none. Conflicts of interest: none.