Comparison of acromio-axillo-suprasternal notch index with upper lip bite test and ratio of height to thyromental distance for prediction of difficult intubation: a prospective study

Preoperative evaluation of airway helps anaesthesiologists to make a strategy to secure airway to prevent life-threatening complications. The aim of the study was to compare the acromio-axillo-suprasternal notch index (AASI), the ratio of height to thyromental distance (RHTMD) and the upper-lip-bite test (ULBT) to predict difficult laryngeal visualization  preoperatively.

 Method: A total of 240 adult patients in American Society Anaesthesiologist physical status (ASA) I and II requiring general anaesthesia for routine surgery were enrolled. The airway was evaluated on the acromio-axillo-suprasternal notch index (AASI), upper lip bite test (ULBT), and the ratio of height to thyromental distance (RHTMD) for all enrolled patients.  An experienced anaesthesiologist, not aware of the recorded preoperative airway evaluation, performed the laryngoscopy and laryngoscopic view was graded as per Cormack and Lehane classification. Primary objective was to assess the efficacy of AASI for prediction of the difficult airway. Secondary objective was to compare it with the RHTMD and ULBT.

 Results: Difficult visualization of the larynx (DVL i.e: Cormack Lehane III and IV) was observed in 33 patients. Higher sensitivity 93.94%, specificity 97.58%,  PPV 86.1 %, diagnostic accuracy (97.08%  ) with  low false positive  (5)  was  for  AASI  as compared to the  ULBT with the sensitivity of 42.4%, specificity of  87.7%, PPV 35% and diagnostic accuracy 81.25%  and  the corresponding value for the RHTMD was  75.76%,  47.34%, 18.66% and 51.25% respectively. Thus suggest, AASI to be superior to the RHTMD and the ULBT in the prediction of difficult visualization of the larynx. The area under the curve for the receiver  operating curve ( AUC of ROC ) of AASI  (0.965,95 %CI=0.93-0.98;p=<0001) was significantly higher than the ULBT and RHTMD  (0.720, 95 % CI =0.658-0.776; p=<000.1) and (0.576, 95% CI, 0.511-0.639; p=<0.133)  further, testify AASI to be  superior to RHTMD and ULBT in the prediction of difficult intubation  The best cut-off value for the AASI >0.49 cms, RHTMD < 21 cms  and for ULBT >2  were endorsed for predicting difficulty in endotracheal intubation

Conclusion:  Preoperative assessment value of AASI >0.49 was found to be a good and reliable predictor for difficult visualisation of the larynx.