Evaluation of neck measurements and their correlation with prediction of difficult laryngoscopic view

INTRODUCTION: Preoperative assessment of various anatomic and clinical features helps in identifying potentially difficult laryngoscopy and intubation in advance allowing the anesthetist to be prepared for such a scenario. Though “ Short Neck” is a commonly used term in airway assessment indicating the possibility of a difficult airway. there is a lack of clarity regrading the cut off value and the association of different neck lengths (Anterior, Posterior and Lateral) to the laryngoscopic view. AIM : Evaluation of anterior, posterior and lateral neck length in neutral and extended positions and correlate each measurement with prediction of difficult laryngoscopic view. MATERIALS AND METHODS : This prospective observational study was conducted on 150 patients belonging to American Society of Anesthesiologists (ASA) grade 1/11 , aged 18-65 years with body mass index (BMI) 18 to 35 kg/m2,scheduled to undergo elective surgeries under general anaesthesia with endotracheal intubation. Each subject’s anterior,lateral and posterior neck lengths (ANL,LNL,PNL) were measured pre operatively. Direct laryngoscopy was done to achieve the best Cormack Lehane(CL) grade using manoeuvres (Backward upward rightward manoeuvre(BURP)/OELM/Change of Blade/Change of pillow height/RAMP positioning) when indicated and the same compared to the measured neck lengths. RESULT : The incidence of difficult laryngoscopy was found to be 18 per cent in our study population. Anterior neck length in neutral position was found to be the best predictor of difficult laryngoscopy, with a threshold of less than or equal to 9 cms. No particular neck length correlated with BMI and age. All the neck lengths showed positive correlation with the height of the subject CONCLUSION : ANL with a cut off criterion of less than or equal to 9 cm in neutral position can used objectively when measuring neck length. All neck lengths showed significant change with neck mobility. Rate of change of both PNL and LNL with head extension position showed significant change in difficult laryngoscopy subjects.