Anjum Saghir, Azhar Hussain Bajwa, Humayun Idrees, Abdul Rauf.
Is Ratio of height and thyromental distance an independent risk factor for anticipation of difficult intubation.
J Cardiovascular Dis Jan ;10(3):70-2.

Objective: To estimate whether ratio of height and thyromental distance (RHTMD) ≥23.5 is an independent risk factor for anticipation of difficult intubation. Materials and Methods: This Cross sectional survey was conducted at the Punjab Institute of Cardiology, Lahore, from January 2010 to November 2010. The patients (n= 346) who came for elective cardiac surgery were selected randomly having no hemodynamic instability. We measured thyromental distance (TMD): from thyroid notch to bony point of mentum, in sitting position with neck extension and mouth fully closed by a consultant anaesthesiologist. The ratio of Height & TMD (RHTMD) was calculated for each patient. All the patients were also evaluated for mouth opening and Mallampatti grading. All the inductions were done by another consultant anesthesiologist, and glottic visualization was assessed using modified Cormack and Lehane classification without external laryngeal manipulation. Difficult laryngoscopy in this study was set at Cormack and Lehane classification Grade 3 OR 4. Results: There were 268 males and 78 females with an average age of 51 years (range 18 to 76). There were 51(14%) difficult laryngoscopies( 37 males & 14 females). In normal intubations average height was 160 cm (range 123-190cm) and average TMD 9.4 cm (range 5-12cm) and average RHTMD was 16.7 (range 11.8-25.8). In difficult laryngoscopies average height was 160 cm (range 123-177cm), average TMD was 9.4 cm (range 7.5-12cm)and average RHTMD was 17.2 (11.8-25.4). There were 4 patients with ratio of RHTMD ≥23.5 with only one female patient with difficult laryngoscopy. Sensitivity was 2% and specificity 98%. Odd ratio was 1.93 and p value was 0.28. Conclusion: RHTMD ≥23.5 is not a risk factor for difficult laryngoscopy/intubation and also not a good screening test for anticipation of difficult laryngoscopy viz a viz difficult intubation in our patients.

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